Colour expectations in modern colour workflows - Media Relative Colour Reproduction

Transcription

1 Colour expectations in modern colour workflows - Media Relative Colour Reproduction Results from the project: "Basics for standardization in toner and inkjet based printing" Fogra-Nr

2 Agenda 1.The role of colour in the production chain 2.Colour rendering - what does a colour scientist say? 3.Introducing media relative reproduction 4.How to use media relative reproduction? 5.Applying media relative reproduction 6.Levels of predictability 7.Summa 2

3 1. Colour expectations Internet Tablet PC DVD, Motion Picture Multi Channel Publishing Consistent colour rendering across all media ISO : permit the predictable dissemination of a compound entity to one or more locations. Printing Typical colour gamuts Representing the range of output media Act as an interchange or exchange space Conventional Printing Digital Printing 3

4 2. Colour rendering and reproduction what does the CIE vocabulary says about colour rendering: "Effect of an illuminant on the colour appearance of objects by conscious or subconscious comparison with their colour appearance under a reference illuminant" Hunt, R. W. G. has defined six different levels of colour reproduction (refined by Mark Fairchild) spectral colour reproduction (cultural heritage) colour reproduction (device mode) pleasing colour reproduction (acceptable) colorimetrical colour reproduction (ICC) colour appearance reproduction (CIECAM02) colour preference reproduction (best possible) Don't confuse colour rendering from reproduction 4

5 3. Colour reproduction in the graphic arts Standardization Objective Evaluation required Colour measurement must reflect what we see Colour science provides established means for evaluating small and medium colour differences but not (yet) different colours (seen side by side) when objects are seen in isolation media relative Colour Differences Different Colours 5

6 3. Do we see (assess) all objects side-by-side? It depends media relative (isolated) Side-by-Side use cases Source: PSD Spot colours 6

7 3. But, graphic arts uses only side by side All colour accuracy requirements are currently defined by absolute colour differences (Side-by-Side) During the last years CIEDE2000 replaces more and more CIEDE76 Examples: ISO x ISO for colour displays and many more How many real print jobs are actually in compliances? Often different paper shades are used successfully! ISO :2004 7

8 really? Fogra Webinar, Stop, graphic arts uses media relative for years Tone value evaluation (referring to solid, substrates and tint) Same tone value but E=13 ( E00=8.2) ICC stores all tables relative to the illuminant see Info window in PSH 100 % Cyan 40 % Cyan FOGRA39 IFRA26 8

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13 3. Did you see a difference? FOGRA39 IFRA26 CJV, Ferrari Frontlit PSO Web Coated 13

14 3. Gamut differences of used examples ISOCoatedV2 (ECI) AtoB3 srgb ISOCoatedV2 (ECI) BtoA1bpc ISONews 26 AtoB3 srgb ISOCoatedV2 (ECI) BtoA1bpc PSO Web Coated Standard AtoB3 srgb ISOCoatedV2 (ECI) BtoA1bpc CJV30 Ferrari Frontlit AtoB3 srgb 14

15 3. Stop, graphic arts uses media relative for years So, why not transferring an established principle for colour reproduction? so lets do it, but how "We" could simply do a conversion at the print service provider side by providing a transformation that predicts the media relative aim values and use this for conformance evaluation but, how the print buyer will take notice? and, which method to be used (XYZ scaling, black handling, spectral models, chromatic adaptation etc)? The predictability will be lost Proposal (already included in drafts ISO x and PSD: To add a additional type of colour reproduction and communicate it upfront The print buyer then decides about the pertinent type, depending on the job 15

16 3. Categorization of colour reproductions Colour gamut similarity Visual assessment similar in shape and size very different "Side-by-Side" Identical colours Consistent colours "Alone" Media Relative colours no provisions 16

17 4. How to use media relative reproduction? Reference Actual Print RGB CMYK1 CMYK2 e.g.. ECIV2 Separation e.g. FOGRA39 Re- Separation e.g. Nexpress Perceptiol to ISOCoatedV2 Media relative reproduction 17

18 4 Limits of media relative reproduction wireframe: ECI V2; True colours: FOGRA39 Projection in CIEa*b*-plane E*=90 E00=30 E*=68 E00=17 Colour science understands colour differences but not different colours (yet) 18

19 4 Limits of media relative reproduction Reference Actual Print RGB CMYK1 CMYK2 e.g.. ECIV2 Gamut- Mapping + Separation e.g. FOGRA39 Re- Separation e.g. HPIndigo 19

20 4. How to communicate media relative reproduction PSD: exemplary job sheet Communicate the expectation upfront Communicate level of predictability 20

21 5. Applying the media relative reproduction It is the same way ICC stores the colour data in ICC profiles ICC media relative colorimetry Black point compensation (bpc) is not part of XYZ-scaling Gamut similarity check takes differences in black point into consideration 21

22 5. calculation details 1. CIELAB values of reference and print out E*ab Ref (left): FOGRA39 Actual (right): FOGRA41 4 exempl. patches of the media wedge V3 2. Conversion to CIEXYZ 3. Calculating media relative CIEXYZ-values (D50) 4. Calculating CIELAB-values and CIEDE2000 differences E00 5. Praxis: Apply gamut similarity differences and multilevel tolerancing 22

23 5. Anatomy of MS-Excel spread sheet Side-by-Side Evaluation 5. Media Relative Using the Fogra Excel Spreadsheet normal "Reference" values (Lab) - 42 (MK2) or 72 (MK3) 4. CIEDE normal ("Actual") measurement values (Lab) - 42 (MK2) or 72 (MK3) 3. Gamut Check (Similarity) A, B, C or failed 1.Measuring the media wedge 2.Calculation of media relative CIELAB values 3.Checking similarity of gamuts 4.If passed, Evaluation CIEDE2000 colour differences 5.Result: A, B, C or fails 2.3 Compute media relative Labs for Ref. and currents 2.1 Compute XYZ for Ref. and currents 2.2 Compute media relative XYZ for Ref. and currents 23

24 5. Visualisation of colour reproductions FOGRA39 versus FOGRA45 (Side-by-Side) 24

25 5. Visualisation of colour reproductions FOGRA39 versus FOGRA45 (Media relative) 25

26 6. Levels of predictability Identical colours Proofing [ISO ] Validation Print [-8] PSO ISO PSD ISO x Side-by-Side Level of predictability media relative colours PSD ISO x small differences between reference - print Compare with memory consistent colours PSD ISO x Common Appearance huge gamut differences active researched Side-by-Side Full Colour Ref - Absolute Full Colour Ref - Media Neutral Partial Colour Ref. 26

27 6. Summa Side-by-Side colour reproduction is established ICC media relative colorimetry is used for storage of colour data and now for evaluating the reproduction of colour data Further points of research: how to take care of black point compensation how to extend the gamut similarity beyond checking white and black point Join DPWG and contribute to shape standardization in digital printing 27