ICC color management for print production

Transcription

1 ICC color management for print production TAGA Annual Technical Conference 2002 W Craig Revie Principal Consultant Fuji Film Electronic Imaging Limited ICC Chair of the Graphic Arts Special Interest Group

2 Tutorial outline About the ICC ICC color management concepts Creating ICC profiles Using ICC profiles Defining an ICC-based workflow

3 About the ICC ICC History ICC Objectives ICC Membership Working groups Details from

4 ICC History - some milestones 1990 PostScript Level 2 released by Adobe 1993 FOGRA conference - Intercolor consortium formed 1994 Apple s ColorSync format adopted 1994 Version 2 ICC profile format defined 1995 Windows 95 with ICM 1999 PDF 1.3 has support for ICCBased colorspaces 2000 Photoshop 6 released 2001 Version 4 ICC profile format defined 2002 PDF/X-1a (and possibly PDF/X-3) standardized

5 ICC Objectives Open systems color management Portable, standard color profile format Framework independent of device capabilities Technical basis and broad membership Develop a common understanding of color Not limited to print production Basis of profile connection space is a reflection print which may limit areas of application

6 ICC Membership and Organization Founding members Regular members Honorary members Observers Steering committee Founding members + elected members Chair, vice chair, secretary and technical secretary Lars Borg [Adobe], Uwe-Jens Krabbenhoeft [Heidelberg], Kip Smythe [NPES], Tony Johnson [London College of Printing]

7 Working groups Focus on specific areas Examples: Architecture Working Group Workflow Working Group Graphic Arts Special Interest Group discussion groups + 4 meetings per year

8 Tutorial outline About the ICC ICC color management concepts Creating ICC profiles Using ICC profiles Defining an ICC-based workflow

9 ICC color management concepts Basic colorimetry, CIE standard observer RGB additive and CMY(K) subtractive color models Device independent color Color transforms

10 How we see color Rod cells Cone cells Response of cone cells to different frequencies of light The CIE standard observer CIELab and CIEXYZ standards based on CIE standard observer describe colors as we see them used in both PostScript and PDF

11 Color illusions Additive color Subtractive color Start with black and add red, green and blue Start with white and subtract red, green and blue Many (but not all) colors can be simulated in this way

12 Each device sees color differently Image display Photographic printer How can we convert colors from one device to another? Ink jet printer Digital camera Scanner Printing press

13 Device dependent solution Image display Photographic printer Colour transform jungle Ink jet printer Digital camera Scanner Printing press M x N transforms required

14 Device-independent solution Image display Photographic printer TAG Color transform for device to standard color space and from standard color space to device Ink jet printer TAG TAG Standard colour space TAG TAG TAG Digital camera Scanner Printing press M + N transforms required

15 How ICC profiles work Given a colour calculate ink percentage required to reproduce that colour ICC Profile BtoA tables AtoB tables Standard color space [CIEXYZ or CIELab] Calculate colour produced by given ink percentages Ink percentage [CMYK]

16 Basic color transform elements 1-D LUT curve values count samples stored in profile parametric curve parameters defining one of a standard set of functions in profile matrix e1 e2 e3 e4 e5 e6 e7 e8 e9 matrix coefficients stored in profile matrix with offset e1 e2 e3 e4 e5 e6 e7 e8 e9 e10 e11 e12 matrix coefficients stored in profile multi-dimensional LUT values at each node of the 3- or 4-D table stored in profile

17 Putting the elements together C M Y K CMYK 1-D tables 4-D LUT Lab 1-D tables AToB tag from printer profile L a b e1 e2 e3 e4 e5 e6 e7 e8 e9 matrix parametric curves R G B tags from monitor profile L a b Lab 1-D tables e1 e2 e3 e4 e5 e6 e7 e8 e9 e10 e11 e12 Matrix with offset 'M' 1-D tables 3-D LUT CMYK 1-D tables BToA tag from version 4 printer profile C M Y K

18 Example ICC Profile Header Private A2B0 A2B1 A2B2 A2B3 Public B2A0 B2a1 B2A2 B2A3 ICC Profile Inspector.lnk

19 ICC color management concepts (2) Rendering Intent Profile connection space (PCS) Color Management Module (CMM)

20 Color gamut comparison Solid shape indicates gamut of print process Wire frame indicates gamut of monitor When printing colors viewed on screen some kind of trade-off must be made to determine how we should map one color gamut to the other

21 Gamut mapping depends on page element Company logo Tinted Areas Illustrations Photographs Text

22 ICC Rendering Intents Four ICC Rendering Intents define gamut mapping Absolute Colorimetric: measurement (relative to illuminant) of output color should match that of input color if possible Relative Colorimetric: measurement (relative to paper) of output color should match that of input Perceptual: color images should be transformed to produce desired appearance on the output Saturation: color transforms should maintain saturation in colors where possible

23 Perceptual Intent Color images should be transformed to produce desired appearance on the output - but how? Input profile 1 Input profile 1 Images and input profiles are created independently of the output profile? PCS Output profile We need to agree a means to determine 'desired appearance' with respect to the PCS

24 Profile connection space definition (Perceptual Intent) D50, 500 lux light source Ah yes, not a bad looking virtual print Media White Point has neutral reflectance of 89% (Dmin ) Media Black point has neutral reflectance of 0,30911% (Dmax 2.51) 20% surround CIE 1931 standard colorimetric observer adapted to viewing environment

25 Now we can use Perceptual Intent Color images should be transformed to produce desired appearance on the output Input profile 1 Input profile 1 On input images and/or profiles can be adjusted to achieve desired result on (virtual) reference medium PCS Output profile Output profile creators can assume that images have been adjusted to achieve desired appearance and can perform necessary gamut mapping for printer

26 Open question: How big / what shape is the PCS gamut? This is at present undefined Given the density range that has been defined gives us an idea of size ICC is studying the advantages and disadvantages of defining the PCS gamut more precisely Perceptual gamut mapping is vendor specific - "beauty is in the eye of the profile creator"

27 Color Management Module (CMM) Rendering Intent Profile from document Header Private Public A2B0 B2A0 A2B1 B2a1 Header Private Public A2B0 B2A0 A2B1 B2a1 Profile from printer A2B2 B2A2 A2B2 B2A2 A2B3 B2A3 A2B3 B2A3 Input transform Output transform Combined transform CMM - often part of OS usually more than one option

28 Color Management Module (CMM) Applies transforms implied by profile data No formal ICC definition Why multiple CMMs? Handling TRC profiles Chromatic adaptation Interpolation algorithms Private tags Some minor differences of interpretation

29 Tutorial outline About the ICC ICC color management concepts Creating ICC profiles Using ICC profiles Defining an ICC-based workflow

30 Creating ICC profiles Creating a scanner profile Creating a monitor profile Creating a printer or proofer profile Creating a profile for a printing press Profile testing

31 Classes of profile (1) Input Display Output May be Matrix+TRC type but is more usually LUT-based Must contain at least Device-PCS table for Perceptual Intent Usually Matrix+TRC type but may be LUT-based Must contain both Device- PCS and PCS-Device tables for Perceptual Intent Must be LUT- based Must contain PCS- Device and Device- PCS intents for all Rendering Intents

32 Scanner profile creation Color target for media to be profiled Color target patch colors measured L*a*b* ICC Profile valid for selected media when scanned using reference scanner settings Header Private Public RGB Profiling package constructs profile A2B0 A2B1 A2B2 A2B3 B2A0 B2a1 B2A2 B2A3 Reference scanner settings selected Note the media, scanner model and scanner settings - the profile isn't worth as much without them

33 Digital camera profile creation Obtain standard digital camera color target Measure target patch colors L*a*b* ICC Profile valid for profiled viewing environment Header RGB Private A2B0 A2B1 A2B2 A2B3 Public B2A0 B2a1 B2A2 B2A3 Photograph target in intended viewing environment Select reference camera settings Warning: for a digital camera the viewing environment may be significantly different from that profiled In many cases the use of a standard colorspace may be a better option

34 Creating a monitor profile Measurement of each patch made and passed to profiling package L*a*b* ICC Profile valid for profiled monitor settings Header Private Public e1 e2 e3 e4 e5 e6 e7 e8 e9 RGB Profiling package images colored patches from target in sequence on monitor Note the monitor model, settings (WhitePoint, gamma, brightness, contrast...) and viewing environment - the profile isn't worth as much without them

35 Printer profile creation Establish printer 'reference printing state' and print characterization target Measurement of each patch made and passed to profiling package L*a*b* ICC Profile valid for printer when printing in 'reference state' on profiled media Private A2B0 A2B1 A2B2 A2B3 Header Public B2A0 B2a1 B2A2 B2A3 CMYK patch description CMYK UCR, TAC, Black Printer control etc defined Note the printer reference printing state, media and profile creation parameters (in particular how the black printer was controlled) - the profile isn't worth as much without them

36 Classes of profile (2) DeviceLink Abstract Named color ColorSpace conversion Constructed from a number of device profiles Used by CMMs to cache color transforms Limited applications support Perform PCS-PCS transforms - eg removing color cast Can be used to communicate named color palettes between applications Used to describe colorspaces (srgb->pcs)

37 Component vs Device Link Profiles CMYK Input (A) Input Profile PCS Lab or XYZ Output Profile CMYK Output (B) + New devices require a single profile - Black text mapped to 4-color - 'Dirty yellows' can be a problem - Some profile interoperability problems CMYK Input (A) Device Link Profile CMYK Output (C) + Individual colors can be mapped when the profile is created - New profile required for each input/output combination - Can not be used for Device Independent Color - Limited applications support

38 Creating a profile for a printing press Three options: Profile Individual press the only way if no similar standard printing condition exists Print to standard printing condition relatively small effort to create a profile Use profile for standard printing condition and adjust output to suit individual press a useful route when it isn't possible to print to a standard

39 Profile testing Accuracy measure a profile's accuracy using a reference set of color patches example IT8.7/3 basic set for a printer profile Average and Maximum de can highlight profiles with problems Quality use the profile to process a number of standard test images and view the result example SCID images Color accuracy vs color quality just because a profile produces accurate color does not mean that the result looks good Fitness for purpose make sure that the profile contains all of the information that will be needed by those wishing to use it

40 Tutorial outline About the ICC ICC color management concepts Creating ICC profiles Using ICC profiles Defining an ICC-based workflow

41 Types of color management Image color management scanners, digital cameras, Photoshop Document color management Quark XPress, Adobe InDesign, PostScript, PDF, PDF/X Proofer color management digital proofers, soft proofing

42 Image color management Private Header Public A2B0 B2A0 Header Private Public A2B0 B2A0 A2B1 B2a1 A2B2 B2A2 A2B3 B2A3 Private e1 e2 e3 e4 e5 e6 e7 e8 e9 Header Public Profile and image combination adjusted together to produce 'desired appearance' with respect to either the PCS or a target printing condition Workflow decision: Print-ready CMYK (closed) Profiled and sharpened RGB (open)

43 Document color management Image capture TAG TAG TAG Document elements CMYK RGB Image editing TAG TAG pcmyk pgray prgb Gray Page composition TAG Named Colour

44 Document types CMYK CMYK RGB ICC managed CMYK RGB Badly managed CMYK RGB pcmyk prgb pcmyk prgb pcmyk prgb pgray Gray pgray Gray pgray Gray Named Color Named Color Named Color Colored elements converted to CMYK as soon as possible Named colors converted to process or spot separations Colored elements tagged with appropriate ICC profiles or PostScript CSAs Some elements tagged RGB elements present Incorrect color profiles used

45 Document color management Color managed document RIP color management required C print M print PostScript or PDF to printer - 'desired appearance' Convert to PDF or PostScript PDF or PostScript RIP PDF or PostScript RIP Y print K print C press M press Y press K press PostScript or PDF printed on press - 'desired appearance'

46 Document color management issues Different types of page element managed differently Each image may need to be managed differently Rendering intent selection Output-specific adjustments/selections PostScript and PDF document descriptions Trapping, overprinting and transparency Perceptual Rendering Intent loosely defined Handling device-color elements (default profiles)

47 PostScript colour management Colorspace arrays (CSA) Colorrendering dictionaries (CRD) UseCIEColor mechanism Relationship between ICC and PostScript color management

48 PostScript color model A B C D Image pixel values D 1 D 0 E 1 E 0F 1 F 0 G 1 G 0 D D (D) D E (E) D F (F) D G (G) H 1 H 0 I 1 I 0 J 1 J 0 K 1 K 0 Table A 1 A 0 B 1 B 0 C 1 C 0 D A (A) D B (B) D C (C) L A L B L C M A M B M C N A N B N C L 1 L 0 M 1 M 0 N 1 N 0 D L (L) D M (M) D N (N) X L X M X N Y L Y M Y N Z L Z M Z N X W Y W Z W X Y Z CIEBasedDEFG colorspace CIEBasedABC color space dictionary X B Y B Z B X W Y W Z W X Y Z X B Y B Z B P X P Y P Z Q X Q Y Q Z R X R Y R Z T P (P) T Q (Q) T R (R) Inverse P X P Y P Z Q X Q Y Q Z R X R Y R Z L X L Y L Z M X M Y M Z N X N Y N Z E L E M E N L 1 L 0 M 1 M 0 N 1 N 0 A L A M A N B L B M B N C L C M C N E A E B E C A 1 A 0 B 1 B 0 C 1 C 0 Render Table T 1 T 2 T 3 T 4 C M Y K Type 1 CIE-Based color rendering dictionary

49 PDF/ICC and PostScript Color Models PDF/ICC Workflow RGB or CMYK Input ICC Input Profile [A2B0] [Illuminant] [mediawhitepoint] [ ] ICC Profile Connection Space(PCS) Paper Relative Colorimetry ICC Output Profile [B2A0] [Illuminant] [mediawhitepoint] [ ] CMYK Output ICM ICM RGB or CMYK Input Colorspace Array (CSA) [WhitePoint] [RelativeWhitePoint [ ] CIE XYZ Illuminant Relative Colorimetry Color Rendering Dictionary (CRD) [WhitePoint] [RelativeWhitePoint] [ ] CMYK Output PostScript Workflow

50 Proofer color management ICC Press Profile ICC Proof Profile BtoA tables BtoA tables AtoB tables AtoB tables Step 1: all document color conversion to CMYK performed as if the document will be printed on press Step 2: calculate what colors will be produced for each CMYK when printed on Press Digital proofer simulates a printing press or a well-defined printing process Step 3: calculate what CMYK values are needed to produce those colors on Press B

51 Proofer color management issues Element-based or raster-based color management Preserving black-only elements Avoiding dirty yellows Proofing spot colors

52 Possible extended ICC imaging model Enhanced processing Input appearance Smart CMM Output appearance Appearance model data Appearance model data Header Header Private Public Public Private A2B0 B2A0 A2B0 B2A0 A2B1 B2a1 A2B1 B2a1 A2B2 B2A2 A2B2 B2A2 A2B3 B2A3 A2B3 B2A3 Standard processing Rendering Intent INPUT Standard CMM OUTPUT Rendering Intent

53 Tutorial outline About the ICC ICC color management concepts Creating ICC profiles Using ICC profiles Defining an ICC-based workflow

54 Defining workflow Start with Press definition Decide type of workflow CMYK-early, Profiled RGB, Standard working space (srgb) Establish rules for allowed color data types (PDF/X) Design workflow to minimize color conversions Test individual elements before putting them together Remember: garbage in still produces garbage out Adopting industry standards where possible can save a lot of work!

55 CMYK-early workflow example Create Press profile Proofer profile Proof CMYK CMYK Print CMYK All page elements converted to CMYK of target press Profile for target press included in document Target press profile Alternate press profile Limited re-purposing may be possible Re-purpose

56 Profiled RGB workflow example Create ICC X profile Press profile Press profile Proofer profile Proof ICC1 ICC2 ICC X profile Press profile Print ICC3 All page elements tagged with an appropriate ICC profile Profile for target press included in document ICC X profile Press profile Re-purpose

57 Correcting badly managed documents Default RGB or CMYK profile used to color manage data Default profile Default profile Default profile Press profile Press profile Proofer profile Proof Page element uses DeviceRGB or DeviceCMYK colorspace Default profile Press profile Print Default profile Press profile Re-purpose

58 PDF/X-1a Defined by ISO (ISO ) Designed for 'blind exchange' Based on PDF 1.3, documents must have: all fonts and images embedded all colored elements encoded as CMYK, spot or DeviceN MediaBox, TrimBox and ArtBox defined indication of whether file is trapped or untrapped intended printing condition defined Widespread industry support SWOP, DDAP, Time Inc, RR Donnelley

59 PDF/X-3 Currently being defined by ISO (ISO ) For 'blind exchange' within color managed workflows Based on PDF 1.3, documents must have: all fonts and images embedded colored elements encoded as CMYK or ICCBased (or equivalent) intended printing condition defined MediaBox, TrimBox and ArtBox defined indication of whether file is trapped or untrapped Widespread industry support ECI, FOGRA, Time Inc

60 ICC Characterization data registry Maintained by the ICC secretariat Identifies standard printing conditions Short and long name for each printing condition Details given of how to obtain colorimetric data for printing process RGB data registry currently under construction Referenced by PDF/X-1a and PDF/X-3 standards

61 Tutorial outline About the ICC ICC color management concepts Creating ICC profiles Using ICC profiles Defining an ICC-based workflow Questions and discussion

62 YELLOW GREEN RED GREEN BLUE YELLOW RED BLUE GREEN BLUE