2004
The stability of AM and FM
screenings in different water
conditions – with the mottle under
consideration
En jämförelse mellan AM och FM raster med avseende på
fuktvattnets inverkan på flammigheten i tryck.
Åsa Bergmark
Jenny Löfgren
DEGREE PROJECT
Graphic Art Technology
Nr: E 3112 GT
Graphic Art Technology, 120p
E 3112 GT Year-Month-Day051215
Examiner
Anna Skogbergs
Supervisor at the Company/Department
Steve Suffoletto
15 ECTS
Names
Åsa Bergmark
Jenny Löfgren
Company/Department
Rochester Institute of Technology
Title
The stability of AM and FM screenings in different water conditions – with the mottle under
consideration.
Keywords
AM, FM, Mottle, Water balance, Piling
Högskolan Dalarna 781 88 Borlänge
Telefon: 023-77 80 00 Telefax: 023-77 80 50
This project was performed at Rochester Institute of Technology to get more understanding and
knowledge about AM and FM screenings similarities and differences with considerations of the
mottle. By designing a test form conformed to the specific measurements and printing it on
Heidelberg's Sunday 2000 press, the project group has evaluated the questions that already exis-
ted and the ones that occurred during the project. Hence the first press run left some unexpected
phenomenon therefore another press run was performed. Measurements were performed and
graphs produced in Excel. The project group evaluated the results and from that able to establish
facts and draw conclusions. It has been a great experience for the project group and they have
learnt a lot.
Grafisk Teknologi, 120p
Ditt reg.nummer Månad/År12-04
Examinator
Anna Skogbergs
Handledare vid företaget/institutionen Steve Suffoletto
10 poäng
Namn
Åsa Bergmark
Jenny Löfgren
Företag
Rochester Institute of Technology
Titel
En jämförelse mellan AM och FM raster med avseende på fuktvattnets inverkan på flammighe-
ten i tryck.
Nyckelord
AM, FM, mottling, vattenbalans, gummiduksuppbyggnad,
Högskolan Dalarna 781 88 Borlänge
Telefon: 023-77 80 00 Telefax: 023-77 80 50
Detta projekt är utfört på Rochester Institute of Technology med syfte att få mer försåelse och
kunskap om AM och FM rasters likheter och olikheter med avseende på flammighet i tryck.
Genom att trycka en specialdesignad testform på Heidelbergs Sunday 2000 rulloffsetpress, och
utföra mätningar och analyser baserade på denna, har projektgruppen utvärderat de frågor som
fanns ursprungligen, samt de som uppstod under projektets gång. På grund av vissa oförklarliga
uppkomster efter första tryckningen utfördes ytterligare en tryckning. Mätningar utfördes på test-
formen och grafer producerades i Excel. När projektgruppen hade utvärderat resultaten kunde
vissa redan antagna fakta bekräftas samt slutsatser dras. Dock är inga slutsatser definitiva utan
vidare forskning är nödvändig. Det har varit en bra erfarenhet för projektgruppen och de har tagit
stor lärdom.
Foreword
We would like to thank everyone who made this project possible:
– Barbara Birkett who arranged everything and has been a great support in everything regarding our visit at Rochester Institute of Technology.
– The foundation of Ljungberg and the School of Print Media for the eco- nomical support.
– Printing Application Lab, Industry Education Programs and School of Print Media for the time and effort you gave us. Especially:
* Steve Suffoletto
* Dan Clark
* Bill Pope
* Fred White and the web press crew
* John Dettmer
* Bill Garno
– Anna Skogbergs for all the help regarding the report
List of content
1 Introduction 8
1.1 RIT 8
1.2 PAL 8
1.3 Background 8
1.4 Purpose 9
1.5 Goal 9
1.6 Method 9
1.6.1 Sequence of work 9
1.7 Scope 10
2 Preparatory studies 11
2.1 Screening technique 11
2.1.1 History 11
2.1.2 Halftone sreening 11
2.1.3 AM screening 11
2.1.3.1 Dot shapes 12
2.1.3.2 Dot angles 12
2.1.3.3 Moiré 12
2.1.3.4 Rosettes 13
2.1.4 FM screening 13
2.2 Dot gain 13
2.3 Piling 14
2.4 Print density 14
2.5 Ink/Water balance 15
2.6 Mottle 15
2.6.1 Background 15
2.6.2 Different types of mottle 15
2.6.3 Quantifing mottle 16
2.7 Measuring colors 16
2.7.1 Densitometer 17
2.7.2 Spectrophotometer 17
2.7.3 CIE standard observer 17
2.7.4 CIE lab 17
2.7.5 Visual judgement 18
3 Accomplishment 19
3.1 Research 19
3.2 The test form 19
3.3 Plate making and measuring 21
3.3.1 Repeatability and reproducibility 21
3.3.2 Lithocam plate reader 21
3.3.3 X-Rite Dot 21
3.3.4 X-Rite 528 spectro- densitometer 22
3.3.5 X-Rite 938 spectro- densitometer 22
3.4 Choice of paper 22
3.5 The press 22
3.5.1 Press description 23
3.5.2 The press run 23
3.6 Discoveries 24
3.6.1 First press run 24
3.6.2 Second press run 25
3.7 Objectivities 25
3.7.1 AM and FM equivalents 25
3.7.1.1 Density and Dot gain curves 25
3.7.2 Mottle 25
3.7.2.1 Visual judgement 25
3.7.2.2 The analyze with Verity IA 26
3.7.3 Dot gain in 10 micron 26
3.7.3.1 Plate measurings 27
3.7.3.2 Magnification with a microscope 27
3.7.4 Piling 27
3.7.5 The neutrality in black 28
3.7.5.1 The ink bleach test 28
3.7.5.2 The little joe 28
3.7.6 Density variations 29
4 Results 30
4.1 AM and FM equivalents 30
4.1.1 Dot gain 30
4.1.2 Density 31
4.2 Mottle 31
4.3 Dot gain in 10 micron 38
4.4 Piling 40
4.5 The neutrality in black 41
4.6 Density variations 41
5 Conclusion 42
5.1 AM and FM equivalents 42
5.2 Mottle 42
5.3 Dot gain in 10 micron 42
5.4 Piling 42
5.5 The neutrality in black 42
5.6 Density variations 42
6 Discussion 43
7 References 44
Appendix A (1)
Time plan
Appendix B (15)
Density and Dot gain curves
Appendix C (1)
repeatability and reproducibility
Appendix D (1)
Lc and ab curves
Appendix E (1)
printed test form
1 Introduction
This project was performed at Rochester Institute of Technology in coopera- tion with Printing Application Lab, sponsored by the School of Print Media.
1.1 RIT
RIT, Rochester Institute of Technology has probably the world's best edu- cation with concentration on print technique. This University is located in Rochester, NY, USA and started up in 1829. RIT has 15 000 students and 270 educational programs. RIT includes eight colleges and each col- lege has their own amount of schools. The college Image Art & Sciences contains six schools, which one is SPM, School of Print Media. This school offers Bachelor's and Master's degree and even Doctorate examination in print technology.
1.2 PAL
RIT has extensive graphic resources, which gives the students more prac- tical experiences, this in turn makes it easier to understand the graphic workflow. The printing equipment consists of printing presses for web off- set, sheet fed offset, digital printing, gravure printing, flexography and also a comprehensive prepress lab. This division of the school belongs to PAL, Printing Applications Laboratory. PAL is made up of a team, facili- ty, which works with printing, paper and material evaluations and has today achieved a substantial confidence to the industry that engage them.
1.3 Background
For over 125 years the printing industry has used the basic screen tech- niques to produce photography images. Today there are two kinds of screening types to create halftones: Conventional amplitude modulated (AM) screening and frequency modulated (FM) screening.
AM screening varies the size of the dot to simulate different shades of color. It is currently the screening method used most often in printing, because the pitch and angle of the dots are fixed, and the method achieves consistent tonal reproduction. But there are some issues that come with this screen type. Because the halftone dots are spaced and at angles, AM scree- ning is prone to moiré. Other problems include jaggedness and segmenting of fine lines and tone jumping in gradation areas. These problems have also hindered the transition to fully digital workflow, the adoption of computer- to- plate (CtP), and the streamlining of the color proofing process.
FM screening is a relatively new screen process, which can achieve a higher print quality if performed correctly. Unlike AM-, FM screening place micro-dots of equal size randomly, varying their density to produce light and dark tints. Without screen angles, this screen technique elimi- nate moiré. Since FM screen was developed in 1994, the printing indus- try has achieved more knowledge about its benefits, such as sharpness, smoother tone rendering and larger color gamut.
But still there are hesitations about using FM screening. FM screening
demands an extremely strict print production environment, which results into higher printing costs. This is because FM has less tolerance for vari- ations in the process compared to AM. Research and experience show that FM causes greater dot gain, which is one important parameter that makes it more difficult to print mid tones and shadow areas consistently.
Unfortunately, these drawbacks have kept FM screening from being more widely implemented. For the industry too take advantage of all FM's benefits, as soon as possible, it is of most importance they get more know- ledge about FM screening and how to manage it in the best way.
1.4 Purpose
The primary purpose with the project is to determine the water/ ink “win- dow” for AM and FM. Is AM or FM more sensitive to variations in the water balance? What happens if you add too much water? Are there any differences between the reaction in AM and FM? What AM vs FM resolu- tions are equivalent to each other?
The secondary purpose is to investigate water interference mottle in AM and FM? Is it true that FM is more sensitive to mottle, if that is the case, in what tone value? How does the water affect the mottle?
Other purposes is to determine piling for AM and FM and to look at the dot gain of 10 micron.
1.5 Goal
The goal with this project is to achieve better understanding how the AM and FM screens affect the printing quality and how tolerant they are to the changes that are performed during the pressrun. And from that, draw some conclusions that may be a way to bring more knowledge and under- standing about the FM technique.
1.6 Method
A single test form provided by the project group was printed on RIT's Heidelberg Sunday 2000 heat set web offset lithographic press.
Examinations will be done on the printed sheet at PAL (printing applica- tion lab). With help of measuring, analysis, statistics and visual judg- ments the printing was evaluated and conclusions could be drawn.
1.6.1 Sequence of work:
– Meetings with PAL to decide subject
–Research was performed by reading books, articles, papers and scripts and by having discussions with knowledgeable people.
–The test form was designed in consideration of the purpose of the project and was created in a computer program.
–The plates were made in help of a CtP (Computer to Plate). Plate control measuring was also a main part of this process step.
–The test form was printed with Heidelberg Sunday 2000 heat set web offset press.
–Measuring some quality parameters with spectro- densitometer was the further step.
–Visual judgment was made for deeper investigations of some quality parameters.
–Analysis and statistics was the final step in the project. With this conc- lusions could bedraws.
– Report writing
1.7 Scope
One limitation for this project was that only one color, black was used. It is also only one specific ink, blanket, plate, paper and print technique that is used. Further the test form limits the measurings.
2 Preparatory studies
2.1 Screening technique
2.1.1 History
Halftone imaging dates back to the very beginning of photography. The earliest surviving photograph from 1825 is not an image captured with a lens, but a contact reproduction of an engraving. In such an engraving, lines in a grid are spaced and weighted to generate tones in a manner that conceptually is identical to the modern halftone dot.
In 1881 George Meisenbach laid the basis for screening by inventing the auto typical halftone process that is still used today. Using a structu- red grid, Meisenbach created repeatable screenings, that is continued tone reproductions. Meisenbach's work on breaking up an image was pur- sued and refined by industrial reproduction technology.
Further in 1886 it was Fredrick Ives with Lois and Max Levy that dis- covered the first practical photographic halftone method. It was from this result that they discovered the halftone process as well. The technique was about cross line glass that had a grid uniform and pattern that, during exposure, formed a dot shape. Today's computer generated halfto- nes still are created on a grid, but are now in digital form rather than rules etched in glass.
2.1.2 Halftone screening
We see the world as gradation of tone and color. To produce the tone gra- dations with printing presses and digital printers the tones in an image must be broken down into a pattern. This pattern however is created from lots of tiny dots. The tiny dots create the optical illusion of tone grada- tions, hence the term “halftone image”. The dots are so small that the eye can not distinguish each dot, but sees a mixture of the total amount of the ink and light reflected from the paper. The halftone illusion enables a four color press to create the appearance of thousands of colors.
2.1.3 AM screening
The conventional way to produce a photographic image is to use amplitude modulated (AM) screening. Amplitude means size; AM screening breaks up an image into dots of varying sizes to simulate the original image.
To create digital halftone dots, computer software applies a halftone screen grid, (using an algorithm), to a grayscale image. The screening algorithm composes halftone “cells” where pixels are imaged to produce the desired tonality. Each halftone cell is assigned a different sized dot to represent the image data for the cell. Dot area is determined based on the lightness or darkness of each pixel in the image, and then a corresponding bitmap image is created to represent those tones for each process color.
When viewed at a normal distance the area of dots resemble tones of the original image. The greater the number of screen dots per image area, the
more natural the effect of the image. The term screen ruling (or screen frequency or mesh) is used to define the closeness of the screen dots to each other. When observing a 60 lines/cm screen at normal reading dis- tance (approx. 30 cm), the eye is usually no longer able to detect the indi- vidual dots. The frequency of dots is normally measured in lines per inch (lpi). Increasing the frequency, or lpi, of an image allows finer detail to be resolved. The standard for publication printing, SWOP, is based on a 133lpi screen, while GRACoL, the guide for commercial printing, is based on 175lpi.
In AM screens the halftone cells are arranged on the grid at regularly spaced intervals. Screen ruling, or mesh, refers to the resulting frequen- cy of dots and is measured in lines per inch (lpi). Increasing the frequen- cy, or lpi, of an image allows finer details to be resolved.
2.1.3.1 Dot shapes
Common AM dot shapes include round, diamond, square and elliptical.
The reasons for the different shapes are to reduce incalculable dot gains, optimize color stability, and form an industrial standard. When using CtP imaging, for example, it is an excellent choice to use round dots. This is because it is easy to compensate the dot gain with tone reproduction cur- ves. In other cases, for using film imaged plates, considerations have to be given about the benefits or drawbacks that the different dot shapes give. The different dot shapes fit differently to specific projects.
2.1.3.2 Dot angles
When two (or more) AM screens are printed on top of each other a visu- ally objectionable pattern known as moiré may occur. To avoid this pro- blem, screens are rotated away from the horizontal or vertical axis. A screen is very noticeable when positioned at 0 degrees and is least visible when rotated 45 degrees. That is the reason; black halftones are com- monly printed with 45 dgrees angled screens. The least visible color, yel- low is placed at most visible angle 0 degrees, while cyan and magenta are placed between these two at 15 degrees and at 75degrees.
2.1.3.3 Moiré
Improper positioning of color separations causes interference, or so called moiré patterns, which might severely impair the image impression. The printer can almost completely prevent the for-
mation of visible moiré patterns in this way, but, because interference is interrelated with the image structure, it is impossible to entirely avoid these visual disturbances. With finer screen ruling it is possible to decrease moiré pattern.
With originals having a distinctive, fine structu- re of their own, structure related moiré may occur and is virtually unavoidable.
Moiré
2.1.3.4 Rosettes
In spite of the optimal angle formed when attempting to reduce interfe- rence effects/moiré phenomena, rosettes may form in homogeneous color areas in particular. The formation of a rosette also depends on the relati- ve positioning of the color separations to one another. Also with rosettes pattern, it is possible to decrease it with finer screen rulings.
2.1.4 FM screening
Frequency modulated (FM) screening is a relatively new screening tech- nique (1994), which lets users output high quality color images at lower resolutions. This is possible by using micro- dots, much smaller dots than conventional halftone dots. Compared to AM-, FM screening keeps the dots the same size and varies the frequency, or number, of dots and the location of those dots to simulate the original image. So instead of crea- ting dots in fixed locations on a grid, you use fixed- size dots that are arranged closer together or further apart to represent different shades.
In FM screening, the concepts of screen angle and frequency no longer apply, so no problems with moiré will occur. Other benefits with FM includes; sharpness, smother
tone rendering and larger color gamut. But still there are draw- backs keeping FM screening from being more implemented.
FM is more sensitive to varia- tions in the process, so to consi- der the benefits of FM it is important to have perfect con- trol during the whole printing process. Great dot gain is an issue that makes it harder for FM, than for AM to achieve con- sistent tonal reproduction.
2.2 Dot gain
Dot Gain is the effect of halftone dots growing in area between the com- puter file and the printed sheet. Dot gain effects the full tint range, so ima- ges darken, loose contrast and details in the shadows. Each step in the process distorts the dot to a point where it is no longer the percent value prescribed in the original file. Dot Gain is present to one degree or another in every printing process and it is impossible to avoid. So instead, what the industry is working with is to foresee it in the best way. The following list presents those factors that influence dot distortion in lithography.
– Ink film thickness. The thicker the ink film, the greater the dot gain.
– Impression pressure. The greater the pressure, the greater the dot gain. Pressure may be adjusted by plate and blanket packing and/ or cylinder position adjustment.
– Offset blanket. Compressible blankets distort less than conventional blankets and thus produce less dot gain.
AM FM
– Ink/ water balance. Too much water feed causes the ink to become waterlogged which, in turn, causes greater dot gain.
– Press speed. Increased speed tends to decrease dot gain, assuming the press is in good mechanical condition and is properly adjusted.
– Paper factors. Smoother papers and papers with more coating exhibit less dot gain. This is a factor that is conclusive for the optical dot gain as well, which has to be taken into consideration.
– Ink factors. Higher- tack inks and inks with higher pigment concen- tration exhibit lower dot gain.
So, what started as a 50% tone in the original file, might gain about 5%
when it is exposed to the plate in vacuum frame (chemical dot gain) and another 5% as the dot transfers to the blanket, and yet another 5% as the dot transfers to the paper (mechanical dot gain). Further, as light hits the dot of ink and scatters through it and the paper, a small shadow is for- med around the dot. This adds another 6% dot gain (optical dot gain). The 50% dot in the original file is now a 71% dot on the press sheet. A tone that grows from 50% to 71% is said to have 21% dot gain.
In the attempt to standardize offset printing, standard values have been specified for the dot gain from film to print. It is the printer's job to achieve the standard for dot gain by appropriately selecting materials and making suitable press adjustments.
To measure dot gain the printing operators are using a densitometer.
To get the dot gain value, coverage measuring is performed in solid and halftone patches (50% US standard), and further estimated as the formal beside. Why you need the value from the 50% patch is because of the cir- cumference of the halftone dot is greatest, and thus the gain is greatest at the same size.
2.3 Piling
Piling is an unwanted defect, which occur when ink or paper fragment builds up on the blanket. In print it look like printed layer. The print industry has problem with this when specially printing with FM scree- ning and in lower resolutions. The problem is usually solved with a lot of stops to wash the blanket. This in turn takes time and effort, and results in more costs. This problem does not occur everywhere in the industry and not all the time, but as long as the main cause is unknown, it gives the printing industry one more reason not to use FM screening hence piling seems to occur more often when FM sreening is applied.
2.4 Print density
Print density is the measurement value of the print color intensity of the printed area. The density is a very important quality parameter to take into consideration. The printing operator always measures the density during the whole pressrun to see if the density is constant and optimal for the specific paper that is used. To know what values they are supposed to achieve, they are taking help of standards. The standard values depends on what paper or what print technique that is used.
2.5 Ink water balance
To successfully print lithography it requires a proper balance of ink and water. When printing traditional halftone screens, the dampening is set to keep the background clean and the inking is set to achieve a desired density. This balance is delicate because too much or too little of one or both in any combination can make it difficult to anticipate the dot gain and to get a constant density. Bad ink water balance can cause a loss of print quality and produce unwanted defects and waste.
2.6 Mottle
2.6.1 Background
Reflective uniformity or mottle that comes up in the print process is a big problem within the printing industry. Mottle is an uneven absorption of the printing inks by substrate between the printing units of a multicolor press, and leads to uneven splitting on the subsequent blankets. Mottle is very complex and it has many causes. It is difficult to describe from obser- vation because of its many variations. Mottle has been described as, “an unwanted laterally varying reflectivity in homogenous tone areas that expresses itself as stochastic ‘cloudiness’ or ‘graininess’ or sometimes in more ordered patterns. It is not visible in text areas, hardly visible in
‘busy’ images rich in details, but may be clearly visible in calmer image parts like skies or homogeneous background tone plates” (Johansson 1992). Mottling is effected significantly by the characteristics of the paper with regard to the homogeneity of its structure and its coating. But it can also be caused by many other factors like composition of the ink, uneven pressures from the cylinders or uneven water balance. The final result of mottle is often occurred in a combination of these.
2.6.2 Different types of mottle
Paper formation and surface mottle is the most basic set of mottle and depends on the characteristics of the paper. Variations in the density, surface smoothness, fiber content, fines, filler content, sizing, surface pH, and specific energy of the paper can have a dramatic influence on the abi- lity of an ink to transfer onto the surface, its absorbency, wicking, pene- tration and drying characteristics. Uneven fiber distribution within the sheet (formation) is often at the root of these effects since the formation also influences the retention of fines and additives. A poor mass distribu- tion also has a negative influence on the light scattering coefficient of the paper as well as its opacity.
Backtrap mottle occurs when the ink has problems transfering from the print blanket to the paper. Typically caused when the ink is unstable or the solvent/oil is lost too quickly, any non-uniformity in the ink transfer rate can create a mottle appearance. Backtrap mottle usually appears in first down inks, and is sometimes a result of improper ink pH or viscosity for the paper being used. Low viscosity inks sometimes produce an appea- rance called “orange peel,” named for the pattern that the ink creates.
Wet ink trap mottle is the type of mottle that occurs when it is an incor-
rect ink tack or pH sequence. Usually a second down ink appears mottled when it is printed over a first down ink, but appears unmottled when printed alone on the substrate.
Density mottle occurs with uneven pressures between metal type, gra- vure cylinder or offset blanket and paper. Not as common in lithography, but can be seen as a result of a smashed blanket.
Gloss mottle is caused by paper's nonuniform absorption resulting in portions of the ink to appear glossy and others matte. Ink improperly for- mulated for a particular paper is also a contributor to gloss mottle.
Dry trap mottle, also called crystallization occurs because of excessive dry time between runs of a multicolor job on a single color press or impro- per wax content in a set of ink. As ink dries, wax migrates to the top sur- face. Excessive wax migration to a dried ink surface can make the adhe- sion of subsequent inks difficult because the surface becomes slippery, hard and smooth.
Water interference mottle (WIM) appears when paper does not absorb the fountain solution, which reduce the ink's ability to transfer to paper.
Typically, WIM is caused by excessive water, improper ink formulation, inadequately mixed solutions, or excessive alcohol.
Another cause for mottle can be variations in impression caused by incorrectly mounted plates, press bounce, drive gear marks, fluting etc.
2.6.3 Quantifing mottle
At any level of magnification, it is the spatial distribution of the transi- tions from one luminance level to another that determines the degree of mottle. From an image analyses perspective, the phenomena we refer to as mottle is composed of at least two independent effects, darker and lighter patches. The size and contrast between these patches cause the “graini- ness” of a mottled sample. So, if the patch areas are small, and/or the con- trast between them is small it is less likely to perceive them as mottled.
Thus, if there is little contrast between light areas and dark areas, the size is unimportant. And the same thing happens if the patches are small, the contrast becomes unimportant since the eye intergrates the patches and perceives a solid print area. Small patches with large contrast are very similar to screen tinting process colors creating the illusion of a solid color.
The methods that are discovered today, to quantify mottle, are based on this approach. These estimates are conceptually simple to understand and are highly correlated to the perceptions of human judges.
2.7 Measuring colors
Measurement is the key to total production control. Using measured color data, we can monitor color at each stage of production and check the “clo- seness” of color matches using repeatable, standardized numerical data.
Color measurement instruments “receive” color the same way our eyes receive color: By gathering and filtering the manipulated wavelengths of light that are reflected from an object. But each type of instrument does something that our eye cannot do: assign a specific value to the color that can be consistently analyzed in terms numeric tolerances and control
limits. The scope and accuracy of these values depend on the measuring instrument. Today the most commonly used instruments for measuring color are densitometers, colorimeters and spectrophotometers. When measuring with a densitometer you get a simple density value and with a spectrophotometer you get spectral values.
2.7.1 Densitometer
Densitometer is the most commonly used instrument, when measuring color. A densitometer is a photo- electric device that simply measures and computes how much of a known amount of light is reflected from – or transmitted through – an object. Densitometers can determine not only the density, but also the parameters that characterize halftone printing, such as dot gain, relative printing contrast and trapping.
2.7.2 Spectrophotometer
A spectrophotometer measures the amount of light reflected by a surface as a function of wavelength to produce a reflectance spectrum. The reflec- tance spectrum of a sample can be used, in conjunction with the CIE stan- dard observer, which is good for specifying color stimuli using tristimulus values for three imaginary primaries.
2.7.3 CIE standard observer
The CIE standard observer is a result from experiments where observers where asked to match monochromatic wavelengths of light with mixtures of three primaries. The standard observer is in fact a table showing how much of each primary would be used (by an average observer) to match each wavelength of light.
2.7.4 CIE lab
CIE Lab is a specification of color perceptions in terms of a three- dimen- sional space. The L*� -axis is known as the lightness and extends from 0 (black) to 100 (white). The other two coordinates a* and b* represent redness- greenness and yellowness- blueness respectively. Samples for which a* = b* = 0 are achromatic and thus the L*-axis represents the achromatic scale of grays from black to white.
2.7.5 Visual judgment
In judgment of color and the print quality it is always important to take into consideration, both physical and physiological effects. The physical components are measurable, the phy- siological are not. With an overview with the eyes it is possible to look at the “over all” impression and see how the print defect looks for real. Because in the end it is a human eye that it is
the judger, not a measure instrument. L*a*b*
The visual judgment is good to have as a complement together with the measured result, to achieve a more accurate conclusion.
To make the judgment fair and useful, there are a couple of parameters that the viewer has to be aware of. Right and/or consequent lighting tem- perature is necessary, to give a similar impression. It is also important to have a good sight; otherwise the investigation turns out meaningless.
Many people have disturbing on their eyes that gives them problem to reproduce color. The surrounding color is also of big meaning, while you understand color differently beside different color.
3 Accomplishment
– Meetings with PAL to decide subject
–Research was performed by reading books, articles, papers and scripts and by having discussions with knowledgeable people.
–The test form was designed in consideration of the purpose of the project and was created in a computer program.
–The plates were made in help of a CtP (Computer to Plate). Plate control measuring was also a main part of this process step.
–The test form was printed with Heidelberg Sunday 2000 heat set web offset press.
–Measuring some quality parameters with spectro- densitometer was the further step.
–Visual judgment was made for deeper investigations of some quality parameters.
–Analysis and statistics was the final step in the project. Of these could conclusions draws. Purpose
3.1 Research
The project began with a couple of meetings with different main people at PAL. During these meetings a topic was chosen that was interesting and useful for both the project group and PAL, which was the purpose. A tutor was also appointed to help and support the project group during the whole time.
Further the project group did research about the topic. This was perfor- med by borrowing and reading books, papers and scripts. Information via Internet and discussions with professors and teachers was also very useful.
3.2 The test form
The test form was designed to investigate piling, the water window for AM and FM, halftone and water interference mottle and to find AM and FM equivalents. To do so the test form was divided in sections dedicated to the different objectivities. All the resolutions were printed linear of the reason that no reliably curves existed at the time. The size of the test form was 32x22 3/4 inches hence the width of the test form was limited to the size of the paper and the length to the size of the plate. The test form was produced in InDesign. The measurements took place on the topside of the sheet. The backside had no print.
To do a fair judgment of the mottle, the size of the squares measured has a big influence. The bigger the area that is measured the more accu- rate numbers you get. And it is also easier to do a visual test if the squ- ares have a moderate size. For that reasons the mottle square size sett- led to be two times two inches. The four resolutions AM 150lpi and 300lpi and FM 20 micron and 10 micron are all represented in the five tints:
10%, 25%, 35%, 50% and 75%. Based on the thesis “Are fine screens an alternative to FM screening?” by Dr Kurt Schläpfer and Erwin Widmer:
quotation: “Thus one potential limitation of FM screening is the visual
noise in the 18-30% tint areas” the project group decided to have a tint between 25% and 50% to make sure that the information presented were accurate. The mottle squares are placed to the left on the test form and the ones in the top are printed with the first unit and the ones below with the second unit.
The next element on the test form is designed strictly to look at prin- ting defects, applied to see if ghosting or reflection occurred during the pressrun. This element is printed only with the first printing unit becau- se the changes in the water balance were performed on this printing unit.
The rendering tone scales are produced to look visually at the mottle, look at the piling and how well the different resolutions can produce a smooth rendering from dark to light areas. The rendering scales are printed in both the first and the second black. The first four scales from the right, repre- senting the four different resolutions are printed with the second unit. The rest of the rendering scales are printed with the first black.
To be able to measure the dot gain and the density in one specific tint and screen squares were created and placed next to the belonging resolution.
The shades of the tints were chosen to go from 10% to 100% in steps of 10%. The squares were made as small as possible hence the only require- ment was that the spectrodensitomers measurement advice had room to perform an accurate measurement. Also it is better to have small areas in
AM150lpi AM 300lpi FM 20 micronFM 10 micron AM150lpi AM 300lpi FM 20 micronFM 10 micron AM150lpi AM 300lpi FM 20 micronFM 10 micron AM150lpi AM 300lpi FM 20 micronFM 10 micron
AM150lpi AM 300lpi FM 20 micronFM 10 micron AM150lpi AM 300lpi FM 20 micronFM 10 micron AM150lpi AM 300lpi FM 20 micronFM 10 micron AM150lpi AM 300lpi FM 20 micronFM 10 micron 50%10%25%35%35%75%10%25%50%75%
1
2
3
4 5
1. Mottle tints first black 2. Mottle tints second black 3. Ghosting and reflection area 4. Rendering scales and tints second black 5. Rendering scales and tints first black
this case to make sure that the same area is measured each time; the dif- ferences in the measured values because of moving is less. The squares are as the rendering scales printed with both black. The squares placed next to the first four rendering scales are printed with the second black and the rest with the first black, following the same system as with the rendering scales.
3.3 Plate making and measuring
The project group made the plates to the first press run. Because of the lack of time, the plates to the second press run were made by PAL. The plate type was a Kodak Polychrome Graphics Gold (positive plate) made on the CtP trendsetter VLF from Creo. The project group performed mea- surments on the plates to make sure that they were ok.
3.3.1 Repeatability/reproducibility
In assurance of the measuring devises accuracy, and to find out which device can produce reliable data (in the sense of repeatability and repro- ducibility) a test was performed. The test was applied on X-Rite 528 (spec- trodensitometer), XRite 938 (spectrodensitometer), X-Rite DotDot meter and Troika Platecam (corresponding to the Troika Lithocam plate reader which is a upgraded version of the Platecam). 30 measurements were per- formed in the same tint on an unused plate. First without moving to look at the repeatability and then with moving, still in the same tint, to look at the reproducibility. The data was used to calculate the standard devi- ation and the range (see Appendix C) Based on this fact it was, decided that the Troika Platecam was the most accurate advice if the sensitive- ness of the pressure applied when taking a picture is disregarded.
3.3.2 Lithocam Plate reader
Lithocam is a measuring instrument, which can read dot percentage, dot image display, screen ruling, dot diameter and screen angle. Lithocam works like an enhanced camera with an optical head, which makes the accuracy high. This measurement can read plate, film and paper dot per- centage and works as an ideal quality control tool. In the plate room for example, this dotometer can identify processor problems, plate coating, chemical and handling issues s well as laser problems.
3.3.3 X-RiteDot
The technique that is used by the X- RiteDot is a further development of densitometry. This instrument can analyze the screen percentage of any hard-dot or soft-dot film on any light table. This is an instrument that can make measurements of any dot image, on prints, plates or films. It is easy to use and it has a full-size graphic display that
shows the visual image can be seen in a magnify- ing loupe.
X-RiteDot Lithocam
3.3.4 X-Rite 528 color reflection spectrodensitometer
This is a combination of a densitometer and a spectrodensitometer (see Densitometer, Spectrophotometer) This instrument can measure a lot of quality parameters and both get simple density value or a spectral value.
3.3.5 X-Rite 938 spectro-densitometer
This is also a combination of a densitometer and a spectrodensitometer (see Densitometer, Spectrophotometer) This instrument can measure a lot of quality parameters and both get simple density value or a spectral value. Comparing X-Rite528 and X-Rite 938, 939 is more precis than 528 and is in turn much more expensive.
3.4 Choice of paper
The test form was printed on Bowater number 5, 40 lb (59 gsm) which is marketed as a LWC paper. This paper was chosen of economical reasons because the project group had a limited budget. Bowater Gloss is used primarily for magazine publication and advertising purposes. The base paper for Bowater Gloss is made up of roughly 45% mechanical pulp and 55% chemical pulp. This base paper is coated with a blend of pigments and adhesives, which accounts for approximately 25% of the finished paper's total weight. Physical properties such as caliper and opacity vary with the weight of the product. Listed below are the typical properties of Bowater Gloss sheet 40lb. (59gsm) Bowater Gloss sheet:
– Brightness 72.0 – Gloss 54.0 – Opacity 89.0 – Color "a*" 0.2
– Color "b*" 1.0
3.5 The press
The project continued with printing the test form at the Heidelberg Sunday 2000, a heat set web offset press. The press is placed at RIT, PAL and is used for printing the schools own weekly magazine and for compa- ny making research type HeatSet.
Heidelberg Sunday 2000 X-Rite 938
X-Rite 528
3.5.1 Press description
Heidelberg Sunday 2000 Heatset Web Offset Press has a maximum speed of 82,000 impressions per hour. It has 6 units over 6 perfecting, and are available with a traditional 16-page cylinder configuration or a wider 24- page configuration. Standard features include gapless blankets, 14-roll convertible inking systems, shaftless multidrive technology and the com- prehensive Omnicon control package. Heidelberg supplies a wide range of splices, dryer, pinless folder and auxiliary options to complement specific press configurations and requirements.
The press is also equipped with a closed loop color control named color Quick from GMI (Graphic Microsystems Inc). The on-web spectrophoto- meter measurement delivers data of ink density to the Microcolor.ink key which perform changes if the density is wrong.
3.5.2 The press run Press Date:
First Press run Wednesday October 6, 2004 from 12.00-14.00 Second Press: run Thursday, October 21, 2004 from 8.00-9.00 Number of Colors and Press Sequence:
Two (2) colors, both black. Sequence is 1-, 2-, 3K, 4w, 5w, 6K for both top and bottom sides. (To achieve water mottle two water plates are placed between the two units with black.)
Test Conditions
1) Setup press on Bowater 40lb, #5, LWC paper.
2) Adjust ink/water for normal 150 lpi AM conditions.
3) Run press with GMI to achieve SWOP target density for both black inks. Let press stabilize. The FM may start to pile in the 10% tints during this condition, perhaps the 10 µm first then the 20 µm. Minimum piling is acceptable. However severe piling accumulation may smash and dama- ge the blankets. If so, stop the press, wash blankets and switch to #5 UPM paper.
4) After achieving target density, turn off GMI's auto closed-loop.
5) Run Minimum Water or Dry-up or Catch-up condition on unit 3 black only. Adjust water feed level down by -3 increments and pull samples until we catch-up and dry-up in the non-image areas. Prior to this, we would expect to first see screen tints filling-in and plugging-up, followed by feathering or tailing at the trail edge of solids.
6) Run Maximum Water or Flood or Washout condition on unit 3 black only. Adjust water feed rate level by +4 increments and pull samples until the solid ink density drops below -0.10 points. There may also be some signs of flood or wash marks at the lead edge of solids.
7) Set water to optimum feed rate, which should be the midpoint of the high-low range. Turn back on the GMI auto close-loop and get samples at target density.
8) Drop-off bottom printing and print 1-side only so any backside show or
strike-through doesn't effect measurement and analysis.
9) Pick samples from each condition
The print performance followed the planned description well, except from one thing, printing on both sides. In the beginning it was a gray tint pla- ced on the bottom side, but when an annoying pattern occurred, it was decided to take it away. Further, the blanket that was used was Day Internationale, type Gapless, series 3000. The Ink manufacturer is Flint Heat Set.
When the pressrun was performed, the project group (in assureance of no mix ups), marked each sample according to their color codes. Each mark of cyan or violet adds up to the condition; two marks of cyan means plus eight and so on.
3.6 Discoveries
When the test form where examined, the project group and their tutor found unexpected printing phenomenon. More people where surveyed, but the problem could not be solved. After considerations with the supervisor of the web press, Fred White, another press run were performed. This because it was no proof to be found if the GMI system was off as supposed.
3.6.1 First press run
One of the printing defects were obvious and discovered right away while the other needed a closer look and support of graphs and tables to determine.
The first phenomenon that where discovered and that could be seen with the eyes, were the difference in the neutrality in black. The 150lpi looked neutral but when going to higher resolutions as 300lpi, 20 micron and 10 micron the rendering scales looked brownish-black. This was something that was new and never seen before. It may be because the test form had a unique design not used before; two different screens with two different resolutions of each (equal to four different resolutions) next to each other; and that made it easier to see the difference in the hue.
When the project group examined the tables made of the density vari- ations in the solid under the different water conditions a contradiction was found. Under normal circumstances the density increases when the water decreases and the density decreases when the water increases. The project group found that during this press run the opposite had occurred.
This was the discovery that made the press crew concerned that the pressrun was not performed as instruted.
Attribute Color
Bowater brown
Water up 4 points cyan
Water down 3 points violet Color codes
3.6.2 Second press run
This pressrun was performed to make sure that the GMI system was shut off.
When examining the test form, the neutrality of the rendering scales looked the same. The density variations in the solids under the different water conditions were not the same. When both increasing and decrea- sing the water the density decreased.
3.7 Objectivities
With considerations of the new discoveries the project group decided to change the objectives. Further investigations of the phenomenon were desirable and of big interest for the project group. Therefore the discove- ries were added to the objectivities. Decisions regarding not to remove any of the existing objectivities were made.
Analyses and statistics have been an important part of this project. The program Excel has been used for making different estimatings, tables and curves which was used for evaluation. When producing the graphs a graph was made with all the settings and from that, copies were produ- ced to easily make graphs that look the same.
The project group examined the four resolutions AM 150lpi, AM 300lpi, FM 20 micron and FM 10 micron.
3.7.1 AM and FM equivalents
To find out equivalents between the two screens a comparison was per- formed using the density and dot gain curves.
3.7.1.2 Density and dot gain curves
The density and dot gain was measured on the four resolutions in all the tints on the first black, and on all the different conditions using the spec- trodensitometer ex-rite 928. The data was used to produce graphs sho- wing the variations between the different resolutions with the same water condition, or the same resolution with all the different water con- ditions (se Appendix.B). To make it easier to overview the effects several different combinations of curves placed together were made.
3.7.1 Mottle
The mottle was examined both with a scanner using the software Verity IA and visually of the project group. After consultation the project group decided to read the 10%, 25% because in theese tints mottle occur the most. The 50% tint was used as in purpose of establish the fact that this tint gets less mottle. The results were combined to make a final conclusion.
3.7.2.1 Visual judgment
To perform a fair visual judgment between AM and FM the project group decided to compare the AM 300lpi and the FM 20 micron based on the result with AM and FM equivalents. The mottle squares was cut out and arranged in piles of 6.
– 10% tint first unit black
– 25% tint first unit black – 50% tint first unit black – 10% tint second unit black – 25% tint second unit black – 50% tint second unit black
From each of the piles best and worst samples were picked. The bets sam- ple was the one with an even print with no dark or light area. The worst sample was the one with most dark and light areas. This was performed by both of the members in the project group individually so that no influ- ence on the choice was made, for the reason that two opinions are better than one. A table was created and evaluated.
3.7.2.2 The analyze with Verity IA
The tests were processed using Verity IA 2000 Mottle analysis software in a high-speed personal computer. This performs visual variability ana- lysis in an objective and repeatable way, presenting numerical values of the visual variation. To perform a measurement with Verity IA, an area needs to be chosen.
The chosen area is scanned with an AGFA Duo Scan graphic arts quali- ty full color flat bed scanner specially designed to eliminate image sha- dows caused by fibers from the paper and heavy ink. The software calcu- lates an average of the shade in four data cells in the previous layer to create one data cell in the new layer from what Verity IA calculates; the standard deviation with the luminance difference in the 256 gray levels that the pixel can reproduce. The number from the standard deviation is then applied to an algorithm to produce a mottle index number. The index number is then presented in an excel file with a header chosen in the Verity IA.
The data from the excel files was used to produce graphs of the mottle under the different conditions. Trend lines were applied to the graphs hence the graphs themselves were difficult to evaluate. The project group made a template with different angles and used that to evaluate the trend lines. From that, a table was made with different angles graded with six different grades. For a decreasing one, two or three minus (depending on how big the angle was) and one, two or three plus for an increament.
From that table the mottle were evaluated.
3.7.3 Dot gain in 10 micron
The 150lpi had as expected the lowest dot gain, the 300 lpi and 20 micron had similar dot gain both higher than the 150lpi. But when looking at the 10 micron you could see a decrease compared to the 300lpi and 20 micron.
This left the test group with a maior question why and if something went wrong during the pressrun. This mainly because the theory is that the smaller dot you use the more dots you need and the more dot gain you get.
The statement that 10 micron had less dot gain than 20 micron was something the project group searched for a theory why. The people con- sulted had some different theories. The plate wearing was one of the maior ideas; hence the plates used were not post baked. To further inve-
stigate this, plate measuring ws performed. Unused plates and plates after the first and second press run were measured with the litho cam (which was determined to be the most precise advise in the preparatory work). A microscope was also used to look closer into the other theory about the dot gain; that the small dots (10 micron dots) were not possible to produce correct. And the reason for that would be the limitations with transferring ink to the small dots.
3.7.3.1 Plate measuring
To examine the greatness of the plate wearing, plates with different impressions were measured. Litho Cam is sensitive to the pressure that the user exposes it with when pushing it on the substrate to take the pic- ture. Therefore it is important to make sure that a sharp picture occurs on the screen before taking the picture.
The measured plates are:
– One unused plate produced by the project group with the same method as the used ones. This plate was not used on the pressrun hence a mista- ke was made. This mistake had no significant matter to the plate measu- ring.
– The plate used in the first pressrun, which had approximately 81 000 impressions.
– The plate used in the second pressrun, which had approximately 32 000 impressions.
All the four resolutions were measured in the tints from 10% to 100%.
A table showing the wearing in the different tints in the four resolutions was produced to make it easier to overview the data.
3.7.3.2 Magnification with a microscope
The microscope had magnifications of 120, 240 and 480. A digital camera and a computer were connected to the microscope and when a sharp pic- ture occurred on the screen, a picture was taken. Pictures were taken of the four different resolutions in the square with the 25% tint produced for measurements of the mottle. The pictures on the 150 lpi and the 300 lpi were taken with the magnification of 240 and the pictures of the 10 and 20 micron were taken with the 480 magnifications. The pictures were analyzed on the screen of the project group and their advisors.
3.7.4 Piling
The investigation made of the piling was performed during the pressrun.
The paper used for this pressrun is not graded as a good sheet. It is a bowater five sheet. Piling was expected because of the fact that the quali- ty of the paper was so poor that fibers and other material, could easily build up on the blanket, and also because printing with high resolu- tion(FM), 10 micron. During the first pressrun sheets were pulled just to investigate how long the press could run without any piling. It was impor- tant to continuously pull the sheet because if ink and other material build up on the blanket it may cause a blanket smash. After the first pressrun,
pictures of the blanket was taken to see if it had any layers of build up material.
3.7.5 The neutrality in black
The rendering scales in the four resolutions were measured in the color space Lab, with the spectro-densitometer ex-rite 928. A graph was calcu- lated in excel from the data. Based on this graph the project group could determine that the 10 micron had a higher value on b* than the other resolutions. 20 micron and 300lpi had also higher values in b* than the 150lpi. The biggest difference was in the 70% tint, where 10 micron has a b* value higher than four and the 150lpi has a b* value of 0.5. Which means a difference of 4.5 in b* (see Appendix D).
To further investigate the reason for this the project group performed tests on the ink in PAL (printing application lab). Two different tests where implemented, one measuring Lab on the ink itself and one where the ink was applied in different thickness on two different types of paper.
3.7.5.1 The ink bleach test
This test is performed on a spectrophotometer measuring only the ink. To do so, the black ink is mixed with a special white ink in a mixture of 0.100g of black and 10.000g of white on a piece of glass. These two inks are carefully mixed together so that no black or white is left only the grey.
When the sample contains only gray, the ink is placed in a special piece of cardboard with a hole in it, covered with plastic film. This sample is covered with a piece of glass and placed in a spectrophotometer where measuring of Lab is performed.
3.7.5.2 The little joe
This is a small devise that is supposed to correspond to an offset press with one color and no dampening device. A special designed component is used to apply the ink in different thickness. The component is a piece of metal with a notch and different depths going from 10 micron to 1 micron.
The ink is applied on the device and transferred to the paper via a blan- ket. The thickness of the ink layer that comes to the paper is approxima- tely calculated with the formula 5x/8 when x is the depth of the notch (see
“ink film thickness” below). Hence each time the ink splits it splits in equ- als; and the procedure with transferring the ink through the blanket to the paper is implemented three times to make a fair thickness of the ink on the paper. The project group did testing on two different papers with the same ink that was used on the pressrun. The paper that was used was the bowater from the pressrun and a thicker paper that were almost blu- ish with a negative value on b*. On the bowater paper testing where also performed with ink from the bleach test.
Ink film thickness
This formula is just used to give the reader of the report an understan- ding of how thin the ink film is. To come up with this formula the project group disregarded the fact that the ink transfers back from the blanket to
the metal component and focused only at the transferring from the com- ponent to the blanket. The project group also assumed that the ink is split in equal parts. The layers have different starting points, hence it is only half the amount of the ink left after the impression before. The second and third impression also includes the ink that is left on the blanket from the impression before.
First layer starting point x gives (x/2)/2=x/4
Second layer starting point x/2 gives ((x/2)/2+(x/4))/2=x/4 Third layer starting point x/4 gives ((x/4)/2+(x/8))/2=x/8 The layers together gives (x/4)+(x/4)+(x/8)=5x/8
3.7.6 Density variations
Even though the second pressrun was confirmed to have been operated with the GMI system off the project group could not be certain that eve- rything else was running as it should. The density variations as they occurred in this project are a big contradiction to what is well known in the industry, and that made the project group unsure how to react on this mat- ter. Another pressrun, where the same testing
was performed, proved that when lowering the water on this specific web press the density decreases. The same experiment was applied in a trial on the sheet fed press at RIT. When the press was running with the normal adjust- ments, the density increased when lowering the water (the opposite to the web press). The idea that the bridge roller had something to do with the density variations occurred. This, mainly because the bridge roller on the web feed press was not in use. Another trial on the sheet fed press was performed this time without the brid- ge roller in use.
normal 1.652
-3 water 1.617 -6 water 1.596 -9 water 1.519 -12 water 1.437
middle 1.614
+4 water 1.61 +8 water 1.613 +12 water 1.598 +16 water 1.541 +20 water 1.496
Density variations under diffe- rent water conditions
4 Results
4.1 AM and FM equivalents
The result is based on the dot gain and the density curves for the four dif- ferent resolutions.
4.1.1 Dot gain
The general impression of the dot gain, was that 150 AM has less dot gain in all water conditions. The second less dot gain has 10 micron FM and most dot gain has 300 AM and 20 micron FM. That 10 micron had less dot gain than 20 micron was an unexpected result. What also can be notice is that 300 lpi and 20 micron is following each other in shape and direction during the whole press run. An expected result that you also can see over all is that the parameter that affects the dot gain most is the most extre- me water condition changes.
Even with looking at the print, the project group can see that 300 lpi AM and 20 micron FM look similar, both in tone reproduction and in the tone rendering.
Dot gain
0,00%
5,00%
10,00%
15,00%
20,00%
25,00%
30,00%
35,00%
40,00%
45,00%
50,00%
10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 110%
Tone values
Dot gain
150 lpi
300 lpi
20 micron
10 micron
Dot gain curves, normal water condition
4.1.2 Density
The curves of the density show that 150 lpi AM has lower density during the whole press run. Second lowest is 10 micron FM and highest density has 300 lpi AM and 20 micron FM. Even in the density curves, 300 lpi and 20 micron are looking very similar, and reacting in a very similar way, when changes in water condition is performed. It is 150 lpi that reacts most when increasing and decreasing water.
4.2 Mottle
The mottle curves show the resulting mottle, in the different resolutions and for two different blacks in the different water conditions. If looking at the differences between the two units blacks, the mottle values for the second unit is higher all over. An other general statement is that 150 lpi has higher values than other resolutions. 300 lpi and 20 micron looks similar to each other and have less mottle values than 150 lpi. The 10 micron does not follow a trend at all.
The mottle table shows no differences in sensitivity for water impact between AM and FM in 25% and 50% tints. But in the 10% tint there was some differences between AM and FM, that could be of use for the conc- lusion. In the visual mottle test the project group noticed more mottle in AM than in FM.
The visual judgement shows that overall AM 300 has been chosen as the worst one and FM 20 as the best one, from both the judgers.
Density normal
0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8
10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 110%
Density
150 lpi
300 lpi
20 micron
10 micron
Density curves normal condition
10% 25% 50%
1st unit 2nd unit 1st unit 2nd unit 1st unit 2nd unit
150 lpi -water + + + - 0 0
150 lpi +water + + 0 0 + +
300 lpi -water - + + + - + - -
300 lpi +water - + + - + + -
fm 20 -water - - - 0 - 0 0 -
fm 20 +water - - - + - + + -
fm 10 -water - - - + + + + + 0 0
fm 10 +water - + + 0 - - - -
Result:
Equal
20 better water window Equal
First black Second black
Best Worst Best Worst
10% -9, 20 micron +20, 300lpi middle, 20 micron +20, 20 micron 10% +20, 20 micron +20, 300lpi middle, 20 micron middle, 300lpi 25% normal, 20 micron +20, 20 micron -9, 20 micron +20, 300lpi 25% -9, 20 micron middle, 300lpi -9, 20 micron -9, 300lpi 50% normal, 20 micron +20, 300lpi middle, 20 micron +20, 300lpi 50% normal, 20 micron +20, 300lpi -9, 20 micron +20, 300lpi
Mottle in 10%, 150lpi
0,00 5,00 10,00 15,00 20,00 25,00 30,00 35,00 40,00
normal -3 water -6 water -9 water middle +4 +8 +12 +16 +20
Conditions
Mottle value
150 lpi 1:st unit -water 150 lpi 2:nd unit -water 150 lpi 1:st unit +water 150 lpi 2:nd unit +water Table from the trend lines, + + + has a steep angle upwards and - - - has a steep angle downwards.
Table from the visual judgement
Mottle in 10%, 300 lpi
0,00 5,00 10,00 15,00 20,00 25,00 30,00 35,00 40,00
normal -3 water -6 water -9 water middle +4 +8 +12 +16 +20
Conditions
Mottle value
300 lpi 1:st unit -water 300 lpi 2:nd unit -water 300 lpi 1:st unit +water 300 lpi 2:nd unit +water
Mottle in 10%, 20 micron
0,00 5,00 10,00 15,00 20,00 25,00 30,00 35,00 40,00
normal -3 water -6 water -9 water middle +4 +8 +12 +16 +20
Conditions
Mottle value
20 micron 1:st unit -water 20 micron 2:nd unit -water 20 micron 1:st unit +water 20 micron 2:nd unit +water
Mottle in 10%, 10 micron
0,00 5,00 10,00 15,00 20,00 25,00 30,00 35,00 40,00
normal -3 water -6 water -9 water middle +4 +8 +12 +16 +20
Conditions
Mottle value
10 micron 1:st unit -water 10 micron 2:nd unit -water 10 micron 1:st unit +water 10 micron 2:nd unit +water
Mottle in 25%, 150 lpi
0,00 5,00 10,00 15,00 20,00 25,00 30,00 35,00 40,00
normal -3 water -6 water -9 water middle +4 +8 +12 +16 +20
Conditions
Mottle value
150 lpi 1:st unit -water 150 lpi 2:nd unit -water 150 lpi 1:st unit +water 150 lpi 2:nd unit +water
