Printing the Expected

Transcription

1 Internet Tablet PC DVD, Motion Picture Printing the Expected Multi Channel Publishing Consistent colour rendering across all media Printing Typical colour gamuts Representing the range of output media Act as an interchange or exchange space The IGF research project Fogra No of the Fogra Graphic Technology Research Association, Streitfeldstrasse 19, Munich, was funded by the AiF under the program for promoting industrial research and development(igf) of the Federal Ministry of Economics and Technology, based on a resolution of the German Bundestag. Conventional Printing Digital Printing 1 Agenda 1. Who and what is Fogra? 2. How about customer expectations? 3. Image appraisal types (for digital printing) 4. From ISO ISO The challenges for image quality assessment 6. Image quality attributes in details 7. Where do we go? 2

2 1. The industry needs independent research In 1951 the german printing industry (small and medium enterprises) decided to put some money together Fogra stands for Forschung im grafischen Gewerbe - research in the graphic arts Fogra is governed/owned by its members (who also constitute the board of directors) neutrality Aiming for an lawyer of the printer - an manufacturer independent organization Similar organizations in US (GATF), UK (PIRA), Switzerland (Ugra), Spain (AIDO), etc Fogra is financed (ca. 5 Million turnover) by 1 Mio. membership fees 2 Mio. research funds from the country/state/eu (based on extensive application) In order to compensate for the remaining losses, Fogra provides regular services such as control wedges, certifications, symposia etc 4 1. Fogra - the service provider in the graphic arts industry Research And development Consultancy, measuring and expert opinions Fogra- Services Committee work and Standardization Dissemination and Training Fogra, active in four fields of activities 4

3 2. What are the customer's expectations? Internet Tablet PC DVD, Motion Picture Multi Channel Publishing Consistent colour rendering across all media Lets ask PDF/X ISO : to 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 5 2. Zero and Full reference Full Reference Consistency Predictability Closer is better Accuracy Do we need to have the same level of accuracy (tolerances)? Certainly not. Are there more expectations? Sure! Zero Reference Make it "Sexy" Match Preferences ISO proposal: Quality types A, B & C 6

4 3. Digital Printing - Types of image appraisal Being able to reproduce the same colour to replace a part or reprint after a while Being able to print without visible banding (uniform). Resolution is depending on distance and size achieving the same colour on totally different substrates Source: R. Blind 7 5. ISO provides 3 levels of predictability Identical colours Proofing [ISO ] Validation Print [-8] PSO ISO PSD ISO x Side-by-Side media-relative colours PSD ISO x small gamut-difference between ref. and print Comparison w. memory consistent colours PSD ISO x Common Appearance big gamut differences Predictability of the final colour - upfront Side-by-Side Full Colour Ref - Absolute Full Colour Ref - Media Relative Partial Colour Ref. 8

5 4. From ISO to ISO Offset Digital Machine Machine wet in wet different technologies Paper Ink Substrates Ink Complex but mostly known behavior of components and their interplay separable standardizeable Highly integrated systems. Hardly separable Define Combinations Define expected outcome 9 4. ISO : The toolbox for image quality Graphic technology - Requirements for printed matter utilizing digital printing technologies for the commercial and industrial production - Part 1: Parameters and measurement methods Scope This part of ISO defines print quality attributes and measurement methods for digital prints. These parameters provide a basis to allow subsequent parts of this International Standard to define acceptable conformance criteria for particular use cases. 10

6 4. Laboratory and Practical criteria "System Check" "Print Check" Colour and surface finish Requirements of unprinted substrate colour accuracy requirements Consistent reproduction of tone values Ink Set Gloss Further criteria Homogeneity Streakiness Background Haze Graininess and Mottle Fill (caries) Inking variation across the format and within the printing direction Further criteria Resolution Line Width Native Addressability Effective addressability Raggedness Blurriness MTF (Modulation transfer function) Register Patterning Further requirements Artefacts Contouring Spreading (misdirected dots, satellites) Use case specific criteria???????? dedicated criteria for systems & printer Potential implementation Consistent colour rendering across all media Conven9onal Prin9ng Digital Produc9on ISO ISO / Contract Proof Valida9on Print Offsetprint Concept, Toolbox Lite Produc9on LFP... 12

7 5. Challenges for image quality assessment When you can measure what you are speaking about and express it in numbers, you know something about it Lord W. T. Kelvin, Lecture to the Institution of Civil engineers, London, 3 May 1883 "All colors must be evaluated numerically". A. Kling, Keynote, Color Management Conference We need objective measures (if possible based on agreed upon standards) The ultimate test of any colour reproduction is the opinion of the person who views it. But opinions differ... R. W. G. Hunt. In: The reproduction of color We need to focus on use cases which provides (full) reference (contrary to no reference) How is print image quality define so far? ISO /8 1,2,3 - Scope, normative references, terms & definitions 4 - requirements 4.1 data data halftone 4.2 digital print substrates coloration rub resistance ink set gloss reproduction limits tone value repro vignettes resolving power margin info gamut 5 - Test methods 5.1 control strip 5.2 test objects, measurements, visual Annexes [A: metal slab B: Certification] 14

8 5. Categorization of image quality attributes Colour reproduction Uniformity System Functional performance Resolution Artefacts Productivity on site reliability etc. Permanence Health, Safety, Environment arbitrary but useful Image quality attributes in details concept: Individual attributes contribute to a recognized overall image quality. (compare the rating of food) Quality Type A Quality Type B Quality Type C Colour Perceptual Resolution Homogeneity Artefacts individual needs 16

9 6.1 Evaluation of the colour reproduction Providing tolerances for the three quality types Providing tolerances for spot colour reproduction based an selected image appraisal types (identical versus media-relative) Common appearance to be added later current candidate of ISO Colour: Number of visual & technical discernible tonal steps 18

10 6.2 Perceptual resolution - concept Testchart-Design Correct Interpretation (Driving) - RIP-resolution Printing - Imaging-resolution Perceptual Resolution Correlate Resolution attributes native addressability effective addressability edge blurriness edge raggedness MTF more to come Print Inspection (visually measurement wise) Perceptual resolution Different tolerances for the pertinent quality levels edge blurriness and edge raggedness legibility Mis-registration ISO candidate 20

11 6.2 Correlates tested so far at Fogra Edge Sharpness (inverse of blurriness) a measure of the average edge profile transition width in the direction perpendicular to the edge using the square Edge Raggedness a measure of the average edge profile variation (50%) in the direction parallel to the edge using the rotated squares with 8 degree JTC1, SC28 WG4 works actively on these measures Further fine tuning is needed Round robin tests are underway Practical aspects of scanner influence, repeatability and reproducibility are yet to be evaluated blurriness and raggedness in detail Raggedness Blurriness Scan 22

12 6.2 Mis-Registration (example) Digital production machine Print Run: 500 Data Path: Device Mode Test elements: 4 Positions Format: SRA measurements for K/C, K/C, K/Y Pos. 3 Pos. 4 printing direction Pos. 1 Pos. 2 A B C Evaluation of homogeneity Homogeneity (uniformity) subjective impression of colour uniformity across a large image that is intended to have a uniform colour. Refers to all types of colour variation: lightness, hue, saturation derivatives of these can be measured separately or in combination Variation geometry: 1D, 2D, periodic, aperiodic, localized, large-scale, and small-scale variation, separately or in combination such as streaks, bands, gradients, mottle, graininess and moiré. 24

13 6.3 Evaluation of homogeneity Development of M-Score: Compute the CIELAB colour differences E00 between neighbouring patches 2. Sum measurements for rows and columns and normalize them. 3. Calculate M-Score M-Score in detail M-Score Meaning Comments 95 Perfect Inkjetprint on proofing substrate showing no visible inhomogeneities > 80 Very Good Print with slightly visible inhomogeneities (e.g. some Mottling). No visible stripes. > 70 Good Print with visible inhomogeneities (Mottling) but almost no visible stripes. > 60 Satisfactory Mottling and stripes visible. Is still accepted by most observers. > 50 Adequate Print with clearly visible mottling and/or stripes. Acceptance is highly dependent on the printed image. < 50 Poor (But sellable) Clearly visible mottling and stripes. Not accepted as high quality print 26

14 6.3 How to use M-Score in a standard. ISO candidate toner based systems based on a evaluation of photo books (toner based systems) Homogeneity: Next steps M-Score works good for toner based systems (i.e. it correlates well with absolute (magnitude estimation) and relative scales (rank order)) It ought to be tested how much similar metrics such as ISO (replacement: ISO 24790) mottle improve the performance It will be evaluated also for inkjet prints Streaks will be evaluated by the Offset method 28

15 6.3. Homogeneity: One word about graininess Rank order experiment test charts different levels of graininess We propose three default viewing distances (50 cm [reading], 100 cm [POP] and 1,5 m [Large Format] Simple evaluation of standard test chart with a standard scanner 29 Why did I leave out ISO 15339? Internet Tablet PC DVD, Motion Picture Multi Channel Publishing Consistent colour rendering across all media Printing Typical colour gamuts Representing the range of output media Act as an interchange or exchange space ISO x ISO ISO x 30

16 Summa Think about customers expectation ISO defines new (old) things: Different levels of quality types (currently A, B & C) Different ways of image appraisal (Sidy-by-Side and media relative) Framework for common appearance (to be added if understood objectively) Defining capabilities of combination rather than individual components A collection of important image quality attributes has been collected and is under testing Setup your workflow accordingly to print the expected Together we can do it The best person to decide what research work shall be done is the man who is doing the research. The next best is the head of the department. After that you have the field of best persons and meet increasingly worse groups. The first of these is the research director, who is probably wrong more than half the time. Then comes a committee, which is wrong most of the time. Finally there is the committee of company vice-presidents, which is wrong all the time. Dr. C. E. K. Mees (Kodak) 32

17 8. If you are close to germany, come by drupa 2012 You got compared anyhow. Here you know the rules and the referee! 33 Brand-new Fogra PSD Backup 34

18 8. The PSD-concept: An overview 1. Output process - control 2. Colour Fidelity prepress large format small format 3. Workflow Consistency Match Preflight PDF/X-Creation PDF/X-Output Altona Test Suite V1 & V2 Profile-handling Light-Audit 35 Common appearance in a nutshell reference actual print RGB CMYK1 CMYK2 e.g. ECIV2 Separation e.g. FOGRA39 Proof to Print Match ISO PT 1/2 RGB CMYK1 CMYK2 e.g. ECIV2 Separation e.g. IFRA26 Proof to Print Match ISO

19 4.Printing can also be done a little different You can print nicely with it and you might achieve similar/identical results But it is not spot on on ISO TVI aims Creative work 37