3 Testform CIA 2015C.Pptx

Test Form for Color Imaging Application 1

Test Form for Color Imaging Application

R. Chung, Professor

Some test forms are used to find out device characteristics; others are used to study or optimize color image quality.

2 Topics

. What and why test forms

. Device-level test forms

. Application-level test forms

. Prepare test forms as PDF

. Inspecting and Printing PDF

. Conclusions

3 Why Test Form?

. Test form is a collection of test elements with known input values. – Resolution | Bit-depth | Device values

. When processing the test form through a hardcopy color imaging device, we can observe and analyze the printed results. – Gradation | Color gamut | Visual demerits | Visual preference

4 Two Types of Test Forms

. We use device-level test form to find out tone and color characteristics of a printing device.

. We use application-level test form to optimize image quality and compare image quality differences between different printing devices.

5 Device-level Test Form

. Color image data are standardized and unaltered.

. IT8.7/3 (basic) – Purpose: SID, TVI, ink trapping, color gamut – Input: Legacy CMYK – Output: CIELAB, density – Reference: TT_2

Due to advancements in color measurement technology, we need to add track marks to automate the measurement task.

6 Device-level Test Form

. CMYK ramps (AM, FM) – Purpose: TVI as a function of screening – Input: EPS files with tagged screening instructions – Output: Visual, density – Reference: TT_2

7 Device-level Test Form

. Resolution (spi, bit-depth) – Purpose: addressability, resolution, gray level, etc. – Input: Hand-coded PostScript saved as EPS files – Output: device addressability (x, y), smoothness of gradation

8 Device-level Test Form

. Color characterization – Purpose: Full data set for device profiling – Input: IT8.7/4 (random), IT8.7/4 (visual) – Output: Spectral, CIELAB

IT874R 3x.TIF is designed to be measured by DTP70, iSis, and Spectroscan.

9 Device-level Test Form

. Total area coverage (TAC) – Purpose: Minimum dot area sum of CMYK that delivers maximum darkness – Input: 3-color neutral plus black – Output: Visual, L*

Test elements with very fine increments can be less useful.

10 Device-level Test Form

. Gray balance – Purpose: Find CMY dot area combinations that yield neutrality at different levels of L* – Input: CMY near neutrals – Output: Visual, CIELAB – Reference: TT_7

Gray balance is a device behavior (output). G7 takes gray balance of a standard printing as a device calibration goal (input).

11 Device-level Test Form

. CMYK ink sequence – Purpose: Find out tonal difference between K-first and K- last. – Input: Two black printing units with one unit print K first, and the other K last – Output: Visual, CIELAB – Reference: TT_8

This is a good example of how research is conducted via test form design.

12 Device-level Test Form

. SCID – ISO Pictorial – Purpose: Find out similarities of pictorial color image quality from standard pictorial test images – Input: ISO 12640 Natural CMYK legacy images – Output: Visual

Psychometric assessment is carried out to determine visual preference or color agreement to a reference.

13 Device-level Test Form

. SCID – RIT Pictorial – Purpose: : Find out similarities of pictorial color image quality from standard pictorial test images – Input: Tagged CMYK TIFF images – Output: Visual

Are you getting sick of the ‘Three Musicians’ image? RIT_SCID images come to the rescue.

14 Device-level Test Form

. Process ink gamut – Purpose: Find out gamut surfaces of single-color and two-color of a CMYK device – Input: Legacy CMYK – Output: Visual, CIELAB

Equal spacing and increment in the colorant (CMYK) space.

15 Device-level Test Form

. a*b* slices – Purpose: Find out gamut boundaries of a CMYK device at constant L* levels – Input: Color patches with equal increment in CIELAB color space

16 Device-level Test Form

. Spot color overprint – Purpose: Predict wet-on-wet overprint color – Input: Pantone colors, ink sequence – Output: Visual, spectral – Reference: TT_8

Another example of designing test form to conduct print media research.

17 Device-level Test Form

. Monochrome – Purpose: Find out how a black- and-white printer renders standard monochrome pictorial image – Input: ISO 12640 SCID – Output: Visual, Density

It’s easier to study TVI by using monochrome than color images.

18 Application-level Test Form

. Application-level test forms contain altered image data and are specific to devices involved and with specific goals in mind. – Some require CMYK images as input, e.g., - AM and FM screening – Some require RGB images for input, e.g., - Effect of assigning different RGB color spaces - Effect of color rendering intents

19 Application-level Test Form

. Pictorial color reference images (PCRI) are created to support these color imaging applications. – PCRI-1 contains sRGB tagged JPEGs (TT_6) - Color patches were generated from image contents

20 Application-level Test Form

. PCRI-2 contains Adobe RGB tagged JPEGs (TT_9) – Color images are grouped into three scene categories: high-key, average, and low-key

21 Application-level Test Form

. Tonal match between AM and FM screening (TT_3; TT_4)

Figure 1. Black transfer curves Figure 2. 150lpi AM - Reference image

AM 150lpi

Before (without curve) After (with curve)

Source profile: Adobe RGB (1998).icc; Destination profile: Sunday2000_FM(033).icc. Source profile: Adobe RGB (1998).icc; Destination profile: Sunday2000_AM(033).icc

AM 300lpi AM 300lpi Comparison of AM and FM screening & Black, 4-color Black and 4-color 4-color black 4-color Black only The images above and below were printed using AM images provided that (a) dot gain differences are recon- and FM screening to illustrate the differences between ciled with the use of custom press profiles for AM and the two. Above is a panoramic shot of the the Gannett FM screening, and (b) process control has been properly Courtyard taken by Professor Bob Chung. The left half of carried out across different signatures. Image courtesy the image was printed using FM screening and the right of Donna Crowe. half of the image was printed using AM screening. The image to the right is a comparison of 4-color black The images below are also printed using FM and AM (left), 4-color (center) and black only (right) printing. screening. The image on the left was printed using FM This image was divided into thirds and each portion screening and the image on the right printed using was converted to show the differences. The image is AM screening. The color should match closely for both courtesy of GATF. FM 21µ Velvet FM 21µ Velvet

FM 21µ Staccato FM 21µ Staccato

22 Application-level Test Form

. Cross-platform color match: offset and NexPress (TT_6)

23 Application-level Test Form

. Gray component  Monochrome replacement reproduction

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3-color CMY + Black = 4-color CMYK

GCR1 GCR1 GCR1

MaxKMaxK MaxK

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24 Application-level Test Form

. Effect of assigning different RGB color space (TT_4; TT_5)

Test Targets 4.0 Effect of Different Source Profile !""#$%&'"&())*+,*,+&(&)'-.$#&/.'!&0# These images were converted from RGB to CMYK using the perceptual rendering intent. The images on the left used ColorMatch RGB as the source space. The images on the right used Adobe RGB (1998) as the source space. !"#"$%&'(')*&*(+%,-%'%(*.%,&'),()%/'$'0,)&%"1%+2*% A#".*$%$,)2+C9%'$*%;-*0%,(%+2,-%/')*6%F=%'--,)(,()%'(%DEF% 3445-6%7$,"$%+"%+2*%8"#"$%&'(')*&*(+%*$'9%0,),+'#%,&')*-% /$"!%#*%+"%+2*%,&')*%0"*-%("+%82'()*%0,),+'#%?'#;*-%"1%+2'+% The CMYK profile was the Heidelberg Sunday 2000 FM profile. Images courtesy of Professor Patti Russotti. 0"%("+%'--"8,'+*%.,+2%/$"!%#*-6%:&')*-%.,+2";+%/$"!%#*-% ,&')*9%H;+%,+%82'()*-%+2*%&*'(,()%"1%0,),+'#%?'#;*-9%+2;-9% '$*%<(".(%'-%#*)'8=%,&')*-6%>"%8"(?*$+%'%#*)'8=%,&')*% +2*%'//*'$'(8*%"1%+2*%,&')*6%>2*-*%,&')*-%'$*%8"(?*$+*0% Input profile: ColorMatch RGB Input profile: Adobe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allery of Visual Interest

Output profile: Sunday 2000 FM Output profile: Sunday 2000 FM

Input profile: ColorMatch RGB Input profile: Adobe RGB (1998) Adobe RGB (1998) Apple RGB

ColorMatch RGB sRGB

Output profile: Sunday 2000 FM Output profile: Sunday 2000 FM 0$,/'0"%1$/,'234 !"##$%&'()'*+,-"#'+./$%$,/ 61 52

25 Application-level Test Form

. Effect of Shadow/Highlight adjustment – Adobe Photoshop image adjustment feature

26 Application-level Test Form

. Non-CMYK pictorial color reproduction (TT_8)

27 Application-level Test Form

. Perceived vs. measured color differences (TT_6)

$E*ab vs. $E*00 colors. CIE continued to develop color difference formulas, 10 $Eab. If a color pair has similar visual difference as the have similar $Eab values, do you see there is a larger color

including $E94 , $ECMC , and $E00. One would wonder which other, we would expect that the color difference between difference in the gray pair than in the color pairs? The Color as Numbers $E serves as the best color ruler. the two color pairs to be similar. On the other hand, if a answer should be ‘Yes.’ Predicted $Eab and $E00 of these

Color has three dimensions and can be specified it by color pair has larger visual difference than the other, we color pairs are shown in the table below. With the $E00 numbers. Commission Internationale de l'Eclairage (CIE) Color as Visual Sensation would expect that the color difference between the two formula, you will find out that color differences among

developed the CIELAB color space in 1976 where three This page and the facing page show five color pairs (gray, color pairs to be different. the five pairs are unequal. Do you notice that the $E*00 numbers, L*, a*, and b*, are used to describe a color. CIE also red, blue, green, and yellow). If you measure the color correlates with visual color difference better than that of Which Color Ruler to Use? developed a color difference formula in 1976 with the symbol, difference between any color pair in $Eab, you will find $Eab?

$Eab, which expresses the total color difference between two out that the color difference is close to either 5 $Eab or Once you verify that the five color pairs within a test page

$Eab 5 $Eab 10

!E 5 Predicted Predicted !E 10 Predicted Predicted

Col or Pa ir !E ab !E 00 Col or Pa ir !E ab !E 00 Gray 5.5 7.9 Gray 9.9 9.9

Red 5.4 2.6 Red 10.8 3.2

Blue 5.6 5.1 Blue 11.6 5.0

Green 3.9 2.0 Green 10.3 3.5

Yellow 4.1 2.4 Yellow 8.8 2.1

46 47 Gallery of Visual Interest

28 Prepare Test Forms as PDF

. Test forms are prepared in their native environment. – Adobe InDesign – Adobe Illustrator – Adobe Photoshop

. The file should be “clean” – Eliminate unnecessay layers via ‘flattening’ – Remove hidden elements – Keep the same size – Check raster files for correct resolution

. Use File > Export (or Save as) > Adobe PDF – Choose the correct PDF, e.g., PDF/X-1a, before saving the PDF.

29 Inspecting and Printing PDF

. Open PDF in Adobe Acrobat Pro. – Check the printer selection and the media selection. Use the printer pre-set when possible.

. Make sure that the device-level test form does not contain ICC profile, i.e., device values are sent to the printer without any alteration. – A good example is a printer calibration target. The other example is a profiling target.

. An application-level test form should contain ICC profiles to define color of the data. – Some RIPs are set to honor source ICC profiles. Some don’t.

30 Conclusions

. A research project begins with a question and is followed by – Hypothesis and objective – Methodology, including equipment, materials, and experimental procedures

. Test form represents an important part of the methodology. – It requires additional resources, e.g., prepress, printing, measurement, data analysis, and documentation to accomplish the goal.