Testing CRPCs and Their ICC Profiles Testing CRPC_ICC.pdf · ICC Profile Generation ! Two sets of ICC Profiles were generated from the CRPCs by the CGATS Committee and distributed

Copyright 2014 RIT – May not be reproduced without permission

Testing CRPCs and Their ICC Profiles

Bob Chung, Professor RIT • School of Media Sciences

Seven CRPCs and their ICC profiles were examined quantitatively and visually. Their ICC profiles serve digital color data exchange well.


Topics

§  Introduction –  ISO/PAS 15339-2 CRPC

§  Objectives –  Tone and color characteristics

of CRPC 1-7

–  Converting color image to smaller gamut using test profiles

§  Testing methods –  Quantitative assessment of

CRPCs

–  Visual assessment of CRPCs

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Introduction

§  ISO/PAS 15339-2 was published in 2014.

§  There are 7 CRPCs to serve digital data exchange and printing standardization needs in the graphic arts industry.

§  Two sets of ICC profiles were made available for evaluation by the CGATS Committee and the IDEAlliance PPC members.

§  RIT tested tone and color characteristics of the CRPCs, and color conversion using these ICC profiles.

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What is CRPC?

§  CRPC (Characterized Reference Printing Condition) is a look-up table that defines the relationship between device CMYK values and color. –  CRPCs enable ICC profile construction and facilitate digital data

exchange in color-managed workflows.

–  CRPCs serve as printing and proofing aims.

–  Process calibration and control aims can be extracted from CRPCs.

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ISO/PAS 15339-2 CRPCs

§  A brief description of CRPCs

CRPC Name Typical use

1 ColdsetNews Newsprint

2 HeatsetNews Improved newsprint

3 PremUncoated Utility printing

4 SuperCal General printing

5 PubCoated Publication printing

6 PremCoated Commercial printing

7 Extra Large Ink jet

CGATS Characterization Data Sets, available for downloaded from the URL:http://www.npes.org/programs/standardsworkroom/toolsbestpractices/characterizationdatasets.aspx

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ICC Profile Generation

§  Two sets of ICC Profiles were generated from the CRPCs by the CGATS Committee and distributed at the 2013 April meeting. –  X-Rite i1 Profiler, version 1.4.2 –  Kodak ColorFlow, version 2.0.2 –  Similar CMYK constraints were used in profile generation.

-  Same TAC, e.g., 320 TAC for CRPC6 -  High GCR -  Black starts at quarter-tone

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Objectives

§  Analyze tone and color characteristics of the CRPCs. –  Quantitative assessment of different CRPCs, including gamut,

TRC, gray reproduction, and TVI –  Visual simulation of pictorial images in different CRPCs

§  Test color image conversion using the supplied ICC profiles –  Converting pictorial images to smaller color gamut

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Method – Quantitative

§  Example -- ∆E distribution as relative frequency (RF) and cumulative relative frequency (CRF) between two datasets (TAGA, 2001).

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Method - Quantitative

§  An example of using 90 percentile CRF of ∆E*ab to correlate with visual ranking No visual difference, < 1.2 ∆E*ab Fair color match, < 4 ∆E*ab Printing conformance, < 6 ∆E*ab Poor color match, > 9 ∆E*ab (TAGA, 2001)

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Printing Validation

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§  Procedures for handling data files –  Create a colorlist (.txt) representing colors of interest.

-  IT8.7/4 (1,617) target -  P2P CMY (25) triplets -  9-patch (CMYRGB, Grey1, Grey2, Grey3)

–  Convert a colorlist from A-to-B or B-to-A LUT in ColorThink Pro 3.0.3 (CTPro) with the use of a profile under a specified color rendering condition.

–  Compute and plot the color and TVI data in Excel s/w or customized spreadsheets.

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§  Procedures for grey reproduction analysis: –  Input a near-neutral CMY colorlist,

sampled from the P2P target, into the ColorThink Pro 3.0.3.

–  Assign an ICC profile in absolute rendering and save as a Lab colorlist.

–  Repeat the above for all ICC profiles.

–  Plot a* and b* values vs. %TV of Cyan of each colorlist.

ID C M Y K1 0 0 0 02 2.0 1.6 1.6 03 3.9 2.7 2.7 04 5.9 4.3 4.3 05 7.8 5.5 5.5 06 10.2 7.1 7.1 07 14.9 11.0 11.0 08 20.0 14.9 14.9 09 25.1 18.4 18.4 010 30.2 22.7 22.7 011 34.9 27.1 27.1 012 40.0 31.4 31.4 013 45.1 35.7 35.7 014 49.8 40.4 40.4 015 54.9 45.1 45.1 016 60.0 50.2 50.2 017 65.1 55.3 55.3 018 69.8 60.4 60.4 019 74.9 65.9 65.9 020 80.0 71.8 71.8 021 85.1 78.0 78.0 022 89.8 84.7 84.7 023 94.9 92.2 92.2 024 98.0 96.9 96.9 025 100.0 100.0 100.0 0

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Results - Quantitative

§  The gamut volumes (in cubic Lab units) of CRPCs are shown in ColorThink Pro 3.0.3. –  The gamut volume of CRPC1 (newsprint) is only 16% of the

CRPC7. –  The gamut volume of CRPC6 (commercial) is 74% of the

CRPC7.

§  The two profiling s/w tools produced virtually the same results in gamut volume (unit: cubic Lab).

! CRPC1! CRPC2! CRPC3! CRPC4! CRPC5! CRPC6! CRPC7!ICC_XR! 84,280& 151,311& 165,764& 253,711& 331,416& 389,023& 525,551&Ratio_CRPC7! 0.16& 0.29& 0.32& 0.48& 0.63& 0.74& 1.0&ICC_CF! 84,241& 151,646& 165,907& 254,005& 331,548& 389,677& 526,194&Ratio_CRPC7! 0.16& 0.29& 0.32& 0.48& 0.63& 0.74& 1.0&&

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§  Outer gamut (n=226) comparison of adjacent CRPCs –  Color gamut differences between adjacent CRPCs are uneven.

-  The largest color gamut difference (at the 95 percentile) is between CRPC3 and CRPC4 (10.9 ∆E00).

-  The smallest color gamut difference is between CRPC5 and CRPC6 (3.6 ∆E00).

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CRF$

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CRPC"(1_2)"CRPC"(2_3)"CRPC"(3_4)"CRPC"(4_5)"CRPC"(5_6)"CRPC"(6_7)"

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§  Grey reproduction ramps of CRPC1 ~ CRPC7 are plotted with a* ramps as solid lines and b* ramps as dotted lines in the same color for each CRPC. –  Grey reproduction begins from a* and b* of the paper color and

moves towards 0a* and 0b* linearly as %TV increases.

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RPC1_a# RPC1_b# RPC3_a# RPC3_b#

RPC5_a# RPC5_b# RPC7_a# RPC7_b#

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RPC2_a# RPC2_b# RPC4_a#

RPC4_b# RPC6_a# RPC6_b#

CRPC 1, 3, 5, and 7 CRPC 2, 4, and 6

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§  Procedures for tone reproduction analysis:

–  Darkness (100 – L*) of CMY triplets (normalized to paper) vs. %TV of C

§  Results

–  The tone reproduction curves (Dk of CMY vs. %TV) are common and linear from highlight to midtone.

–  The shadow end of the TRC is dictated by the Darkness of the maximum TAC.

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CRPC 1, 3, 5, and 7 CRPC 2, 4, and 6

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§  Procedure for TVI analysis –  Plot %TVI (colorimetric) vs. TV for

CMYK ramps

§  Results –  A table of Midtone (50%) TVIs for all

CRPC1~CRPC7

–  TVIs of CMY are aligned. –  TVI is proportional to paper grade.

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%TVI_50 C M Y KRPC1 26.5 26.5 26.5 26.2RPC2 19.6 19.6 19.6 22.0RPC3 19.4 19.5 19.5 22.0RPC4 19.5 19.5 19.4 22.2RPC5 16.5 16.5 16.5 19.1RPC6 16.4 16.5 16.5 19.1RPC7 16.5 16.4 16.5 19.1

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Method - Visual Simulation

§  Procedures for evaluating pictorial images in the Adobe Photoshop: 1)  Create a CMYK test block consisted of pictorial

images and color patches (see visual at right). 2)  Perform color management tasks, e.g., assign,

convert, rendering intent, etc. 3)  Convert the above image to AdobeRGB color

space in absolute intent. 4)  Assemble the RGB images in PowerPoint for

visual assessment. 5)  Examine these images visually, including paper

color and colorfulness of images.

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Results - Visual Simulation

§  Observations –  The larger the CRPC number is, the more colorfulness and

tonality the pictorial image has. -  There is visual similarity or common appearance in how color and

neutrals are rendered in all printing conditions.

–  There is no significant visual difference in the pictorial images assigned to ICC profiles built by the two different profiling s/w tools. -  Slide 19 – Profiles from X-Rite -  Slide 20 - Profiles from Kodak

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Discussion - Visual Simulation

§  Observations –  The AdobeRGB gamut is

sufficiently larger than the CRPC7 gamut.

–  The Color LCD gamut is not the case. Bluish-green colors are clipped by the dispaly.

Hint: Avoid the use of cyan-dominant pictorial images for visual simulation.

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Converting Images to a Smaller Gamut

§  Color management procedures for converting CMYK images from medium-to-small color gamut: 1)  Convert CRPC4_XR to CRPC1 in perceptual intents and

relative intents (with BPC and without BPC). 2)  Convert the above to the AdobeRGB color space in absolute

intent. 3)  Assemble converted CRPC1 images and CRPC1 in

PowerPoint. 4)  Examine visual differences between color managed images and

the legacy (untag) CRPC1 image (next slide).

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§  Observations –  The tonality and color gamut are compressed from CRPC4 to

CRPC1. –  There are subtle visual differences among color converted

(perceptual, relative with and without Black Point Compensation) images.

–  Color converted images using the relative intent with the Black Point Compensation resemble closely to the legacy or untag images, i.e., printing the image file to the destination device without color conversion.

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§  Procedures for analyzing color differences of 6 primaries due to gamut mapping: 1)  The colorlist is the 9-patch from the test block

(300TAC, 100K, and 400TAC excluded). 2)  Open 9-patch.txt and assign ICC_CRPC4 to a

colorlist in CTPro 3.0.3. 3)  Convert the list from CRPC4 to CRPC1 in

relative intent. 4)  Convert the list back to CRPC1 in absolute

intent. 5)  Observe color mapping of converted CIELAB

list in relation to their aims in a*-b* diagram (next slide).

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RPC1_aim$


§  Results –  The color in CRPC4 is at the

start of an arrow. –  The converted color is the

arrowhead. –  The circle is CRPC1 aim point

of CMYRGB solids.

§  Observations –  Hue angle is preserved in the

CRPC4-to-CRPC1 conversion. –  Grey is preserved. –  Chroma is over compressed.

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§  Procedures for analyzing color differences (1,617 colors) between a converted colorlist and the colorlist of destination CRPC: 1)  Open IT8.7/4.txt and assign ICC_CRPC4 to a colorlist in CTPro

3.0.3. 2)  Convert the list from CRPC4 to CRPC1 in relative intent. 3)  Convert the list back to CRPC1 in absolute intent. 4)  Compare ∆Es between the converted CIELAB list and CRPC1. 5)  Include round trip error (B-A-B in absolute intent and compare ∆Es) of the destination profile as a reference (next slide).

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CRPC4-to-CRPC1 vs. CRPC1


§  Results –  The dotted line (left) is the

CRPC1 round trip ∆Eab. –  The solid line (right) is the color

conversion error (∆Eab).

§  Observations –  Despite visual similarities, there

are large ∆Es between the converted image and the legacy (untag) image.

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Conclusions

§  Seven CRPCs in ISO/PAS 15339-2 and their ICC profiles were examined quantitatively and by visual simulation. –  Profiles, built from two profiling s/w tools, performed equally well

to reflect tone and gamut differences of CRPCs.

–  These CRPCs have similar tone and color characteristics. Their ICC profiles should serve digital color data exchange well.

–  Color separation, based on one CRPC condition, does not require color management when printed in any other CRPC conditions.

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References

§  ISO/PAS 15339 (2014) Graphic technology — Printing from digital data across multiple technologies — Part 2: Reference characterization data

§  Chung, Robert, and Shimamura, Yoshikazu, “Quantitative Analysis of Pictorial Color Image Difference,” TAGA Proceedings, 2001, pp.381-398

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Thank you. Q/A

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Bob Chung, Professor Email: [email protected]

RIT • School of Media Sciences

Documents

Testing CRPCs and Their ICC Profiles Testing CRPC_ICC.pdf · ICC Profile Generation ! Two sets of ICC Profiles were generated from the CRPCs by the CGATS Committee and distributed