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Colour management
Content
• Light and colour
• Colour management
• Role of paper in colour management
• Standardised printing
Light and colour
World of Colour - psychological
• Human visual system can discriminate about
• 200 hues
• 500 levels of brightness
• 20 le...
World of colour - technical
• Light is electromagnetic radiation
400 nm 700 nm
pm nm um cm m
Illumination and reflection
Illumination affects colours
Under daylight illumination Under incandescent illumination
Creating colours
380
400
420
440
460
480
500
520
540
560
580
600
620
640
660
680
700
720
nm
Green
380
400
420
440
460
480
...
Colour spaces
• RGB
• used for digital images or for colour displays
• e.g. scanners and digital cameras operate in RGB sp...
Colour spaces
• CIE L*a*b* colour space is the most commonly used
device independent (scientific) colour space in the
grap...
Three dimensions of colour
• Hue
• Chroma or saturation
• Lightness
How to define colour difference
• The most common way to
measure color difference is ∆E
• It is distance between two colou...
∆E – an example
∆E = 1
∆E = 2
∆E = 3
∆E = 4
∆E = 5
However - don’t trust your senses
However - don’t trust your senses
Colour management
The importance of colour in printed
products
• Colour is used to impress
and strengthen the brand of
advertised products o...
What is colour management
• Standardising how colour is reproduced in different
stages of the workflow from camera to proo...
The benefits of good colour management
• Quality of printed products increases
• Quality consistency increases
• Time/mone...
From colour space to colour gamut
• Colour space is a mathematical model to describe
the way colour is represented
• RGB, ...
Colour gamuts
-150
-100
-50
0
50
100
150
-140 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120
b*
a*
Adobe RGB
Coated Offse...
ICC-profiles
• ICC-profiles can
• Describe how a particular device produces colour or
• It can be a abstract colour space ...
ICC output profiles (press profiles)
• ICC output profiles
have two functions
1. To separate images for
printing
2. To sim...
UCR, GCR, TAC
• UCR (under color
removal) and GCR (grey
component replacement)
are methods to
determine, how black is
repr...
Black separation
C 7%
M 36%
Y 45%
K 1%
C 0%
M 33%
Y 42%
K 10%
Isocoated v2 300 Maximum GCR
-100
-50
0
50
100
-100 -50 0 50 100
a*
b*
Gamut mapping with ICC-profiles
• Different rendering intents
• Perceptual
• Rel...
Gamut mapping – an example
Perceptual
Relative
RGB
CMYK
History of proofing
Flat-bed proofing
Analog proofers
1st generation of digital
proofers
Modern digital proofers
Proofing
• Inkjet proofers use more than 4 colour to produce
colours
• CMYK + light cyan + light magenta + different black...
Proofing
• How to match paper shade and light tones in
proofing
• Use same paper in proofing as in printing
• Use proofing...
Simplified workflow
Role of paper in colour
management
Significance of paper in colour management
-100
-50
0
50
100
-100 -50 0 50 100
a*
b*
Colour gamut / paper shade Dot gain
I...
Colour gamut
• Paper defines reachable print density level i.e. colour
gamut
• smooth and dense paper can reach higher pri...
89
90
91
92
93
94
95
96
L*
Paper shade and luminance
Coated fine and MWC's
SC
Hi-brite
LWC
MWC
WFC
-6
-4
-2
0
2
4
6
-6 -4 ...
Paper – the 5th colour
Dot gain (TVI, Tone Value Increase)
• Dot gain is an increase in the area of the halftone dot
40% dot on plate 60% dot on ...
Influence of paper on TVI
• Surface of the paper (mainly roughness) defines dot gain
properties of the paper
Double coated...
• Matte-coated in the standard
actually refers to silk grades (semi-
matt)
• Difference between silk and glossy
grades is ...
Paper classification – shade vs. dot gain properties
Paper shade and brightness
Inkdemand(dotgain-TVI)increases
WFC
MWC
St...
Paper classification in ISO 12647-2
• Classification in 2004 version is almost the same as
in 1996 version
• New developme...
ECI Standard ICC-profiles
Classification examples
Sappi prepress datasheets
• Recommendations for each grade for ICC-profiles as
well as additional information on optical p...
Standardised
printing
1. Paper groups 2. Lab targets for CMYK, RGB
3. Dot gain targets
4. Tolerances for Lab, dot gain
ISO 12647-2:2004
Paper classification in ISO 12647-2
• Classification in 2004 version is almost the same as
in 1996 version
• New developme...
1. Paper groups 2. Lab targets for CMYK, RGB
3. Dot gain targets
4. Tolerances for Lab, dot gain
ISO 12647-2:2004
-120
-100
-80
-60
-40
-20
0
20
40
60
80
100
120
-120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120
a
b
Printing to Lab-target...
1. Paper groups 2. Lab targets for CMYK, RGB
3. Dot gain targets
4. Tolerances for Lab, dot gain
ISO 12647-2:2004
Dot gain
• Dot gain is influenced by
• Printing ink
• Ink concentration, tack, fount emulsion
• Paper
• Roughness, porosit...
Dot gain vs screen ruling
• Dot gain increases with
increasing screen
ruling
• Difference can be
compensated in CTP
0%
5%
...
CTP compensation
• Not only level but also shape of the dot gain curve is adjusted
• Usually iterative process to find ave...
Earlier case - after compensation
• Not a perfect match
• Some fine tuning
needed
0 %
5 %
10 %
15 %
20 %
25 %
30 %
0 % 20 ...
How to control dot gain in CM workflow
dot gain is
influenced=
Standardised printing
1. Find target Lab-values (ISO
12647-2) and corresponding print
density levels
2. Compensate dot gai...
Some examples
on ink
adjustments
Normal densityDensity too low Density too high
Normal dot gainDot gain too low Dot gain too high
Magenta dot gain too highTarget print conditions
Magenta print density
decreased
Sappi CM services
Sappi Offering in Colour Management
1. How to print on Sappi papers – Sappi Prepress
Recommendations
• Recommendations on ...
Colour management services - PQE
• Colour quality check of printed product using
established Print Quality Evaluation (PQE...
CM offering ”pyramid”
Prepress datasheets, customer inquiries,
International co-operation (TC130, ECI,
Paperdam), own rese...
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Colour management

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Description: Colour is used to impress and strengthen the brand of advertised products or the magazine itself Colour management is standardising how colour is reproduced in different stages of the workflow from camera to proofing and printing

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Transcript of "Colour management"

  1. 1. Colour management
  2. 2. Content • Light and colour • Colour management • Role of paper in colour management • Standardised printing
  3. 3. Light and colour
  4. 4. World of Colour - psychological • Human visual system can discriminate about • 200 hues • 500 levels of brightness • 20 levels of saturation • Altogether, we can distinguish 2 million different colours • However, we only have about 7500 words for different colours • It is not sure that people see colours in the same way – they may just have learned to call certain colours by certain names
  5. 5. World of colour - technical • Light is electromagnetic radiation 400 nm 700 nm pm nm um cm m
  6. 6. Illumination and reflection
  7. 7. Illumination affects colours Under daylight illumination Under incandescent illumination
  8. 8. Creating colours 380 400 420 440 460 480 500 520 540 560 580 600 620 640 660 680 700 720 nm Green 380 400 420 440 460 480 500 520 540 560 580 600 620 640 660 680 700 720 nm RGB Cyan Yellow CMY
  9. 9. Colour spaces • RGB • used for digital images or for colour displays • e.g. scanners and digital cameras operate in RGB space • CMYK • used for four-colour prints
  10. 10. Colour spaces • CIE L*a*b* colour space is the most commonly used device independent (scientific) colour space in the graphic arts industry • Colours are defined by the perception of human visual system • In CIE L*a*b* colour space colours can be defined with chroma, lightness and hue
  11. 11. Three dimensions of colour • Hue • Chroma or saturation • Lightness
  12. 12. How to define colour difference • The most common way to measure color difference is ∆E • It is distance between two colours in CIE Lab – colour space • We can distinguish colour difference of ~1-2 ∆E • ∆E is not consistent against human perception across the whole gamut • Newer formulas are suggested like ∆E2000 • ∆E2000 will in the future ISO standards X X ∆E
  13. 13. ∆E – an example ∆E = 1 ∆E = 2 ∆E = 3 ∆E = 4 ∆E = 5
  14. 14. However - don’t trust your senses
  15. 15. However - don’t trust your senses
  16. 16. Colour management
  17. 17. The importance of colour in printed products • Colour is used to impress and strengthen the brand of advertised products or the magazine itself • Colour accuracy in of utmost importance in advertisements and catalogues of colour critical products such as cosmetics, clothes and furniture
  18. 18. What is colour management • Standardising how colour is reproduced in different stages of the workflow from camera to proofing and printing • At the same time colour management ensures that full potential of the materials and processes in question is utilised
  19. 19. The benefits of good colour management • Quality of printed products increases • Quality consistency increases • Time/money savings in prepress through decreased retouching of images and remaking of proofs • Time/money savings in printing through faster colour ok in makeready
  20. 20. From colour space to colour gamut • Colour space is a mathematical model to describe the way colour is represented • RGB, CMYK • L*a*b* • Colour gamut is the volume in chosen colour space that a particular device can reproduce • Colour gamut is usually presented in Lab colour space
  21. 21. Colour gamuts -150 -100 -50 0 50 100 150 -140 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120 b* a* Adobe RGB Coated Offset Uncoated Offset
  22. 22. ICC-profiles • ICC-profiles can • Describe how a particular device produces colour or • It can be a abstract colour space (like working RGB colour space) • There are different kinds of profiles • input profiles (e.g. for scanners and cameras) • display profiles (e.g. for monitors) • output profiles (e.g. for proofers and presses) • device link profiles (mainly for repurposing cmyk)
  23. 23. ICC output profiles (press profiles) • ICC output profiles have two functions 1. To separate images for printing 2. To simulate printing in proofing
  24. 24. UCR, GCR, TAC • UCR (under color removal) and GCR (grey component replacement) are methods to determine, how black is reproduced RGB to CMYK conversion • UCR,GCR, TAC are defined in ICC profile • UCR black replaces CMY in neutral (achromatic) tones • GCR black replaces CMY also in chromatic tones • TAC (total area coverage) defines the maximum ink coverage
  25. 25. Black separation C 7% M 36% Y 45% K 1% C 0% M 33% Y 42% K 10% Isocoated v2 300 Maximum GCR
  26. 26. -100 -50 0 50 100 -100 -50 0 50 100 a* b* Gamut mapping with ICC-profiles • Different rendering intents • Perceptual • Relative colorimetric • Absolute colorimetric • Saturation • PerceptuaI • “Moves" also the colours inside colour gamut in order to maintain the image as natural as possible • Relative • Does not move colours inside the gamut original's gamut printer's gamut
  27. 27. Gamut mapping – an example Perceptual Relative RGB CMYK
  28. 28. History of proofing Flat-bed proofing Analog proofers 1st generation of digital proofers Modern digital proofers
  29. 29. Proofing • Inkjet proofers use more than 4 colour to produce colours • CMYK + light cyan + light magenta + different blacks • Proofing uses absolute colorimetric white point of the ICC profile is taken into account
  30. 30. Proofing • How to match paper shade and light tones in proofing • Use same paper in proofing as in printing • Use proofing paper with similar shade and optical brightener amounts • Simulate paper shade in proofing with ink • Most common way in modern inkjet proofing -7 -5 -3 -1 1 3 5 7 -7 -5 -3 -1 1 3 5 7 a* b* Printing paper shade Proofing paper shade
  31. 31. Simplified workflow
  32. 32. Role of paper in colour management
  33. 33. Significance of paper in colour management -100 -50 0 50 100 -100 -50 0 50 100 a* b* Colour gamut / paper shade Dot gain Influenced mainly by paper!
  34. 34. Colour gamut • Paper defines reachable print density level i.e. colour gamut • smooth and dense paper can reach higher print densities than rough and porous Coated paper Uncoated paper
  35. 35. 89 90 91 92 93 94 95 96 L* Paper shade and luminance Coated fine and MWC's SC Hi-brite LWC MWC WFC -6 -4 -2 0 2 4 6 -6 -4 -2 0 2 4 6 WFC MWC Hi-brite LWC Std LWC MFC SC MFC Std LWC PT3 PT1 Spektrolino D50, 2°, white backing
  36. 36. Paper – the 5th colour
  37. 37. Dot gain (TVI, Tone Value Increase) • Dot gain is an increase in the area of the halftone dot 40% dot on plate 60% dot on paper 20% dot gain Dot gain curves
  38. 38. Influence of paper on TVI • Surface of the paper (mainly roughness) defines dot gain properties of the paper Double coated fine paper High brightness LWC Film coated LWC
  39. 39. • Matte-coated in the standard actually refers to silk grades (semi- matt) • Difference between silk and glossy grades is much smaller than with "true" matt grades Matt Paper gloss, % Roughness-PPS Silk Glossy 0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 0 20 40 60 80 Roughness and dot gain
  40. 40. Paper classification – shade vs. dot gain properties Paper shade and brightness Inkdemand(dotgain-TVI)increases WFC MWC Std LWC MFC UWF SC Hi-brite LWC
  41. 41. Paper classification in ISO 12647-2 • Classification in 2004 version is almost the same as in 1996 version • New developments at ISO TC 130 coming up
  42. 42. ECI Standard ICC-profiles
  43. 43. Classification examples
  44. 44. Sappi prepress datasheets • Recommendations for each grade for ICC-profiles as well as additional information on optical propesties
  45. 45. Standardised printing
  46. 46. 1. Paper groups 2. Lab targets for CMYK, RGB 3. Dot gain targets 4. Tolerances for Lab, dot gain ISO 12647-2:2004
  47. 47. Paper classification in ISO 12647-2 • Classification in 2004 version is almost the same as in 1996 version • New developments at ISO TC 130 coming up
  48. 48. 1. Paper groups 2. Lab targets for CMYK, RGB 3. Dot gain targets 4. Tolerances for Lab, dot gain ISO 12647-2:2004
  49. 49. -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120 a b Printing to Lab-targets • Using Lab-targets to calculate correct print density
  50. 50. 1. Paper groups 2. Lab targets for CMYK, RGB 3. Dot gain targets 4. Tolerances for Lab, dot gain ISO 12647-2:2004
  51. 51. Dot gain • Dot gain is influenced by • Printing ink • Ink concentration, tack, fount emulsion • Paper • Roughness, porosity ink demand • Press conditions • Nip pressure, construction, etc.. • Print density level • Printing plate screen ruling / algorhitms • Process disturbancies • Doubling, slurring
  52. 52. Dot gain vs screen ruling • Dot gain increases with increasing screen ruling • Difference can be compensated in CTP 0% 5% 10% 15% 20% 25% 30% 0% 20% 40% 60% 80% 100% dot percentage dotgain 52 l/cm 60 l/cm 70 l/cm 80 l/cm 90 l/cm 130 l/inch 150 l/inch 175 l/inch 200 l/inch 225 l/inch
  53. 53. CTP compensation • Not only level but also shape of the dot gain curve is adjusted • Usually iterative process to find average level of a certain press • However paper and ink changes should only affect level • should be quite easy to implementate
  54. 54. Earlier case - after compensation • Not a perfect match • Some fine tuning needed 0 % 5 % 10 % 15 % 20 % 25 % 30 % 0 % 20 % 40 % 60 % 80 % 100 % dot percentage dotgain 52 l/cm 60 l/cm 70 l/cm 80 l/cm 90 l/cm 130 l/inch 150 l/inch 175 l/inch 200 l/inch 225 l/inch
  55. 55. How to control dot gain in CM workflow dot gain is influenced=
  56. 56. Standardised printing 1. Find target Lab-values (ISO 12647-2) and corresponding print density levels 2. Compensate dot gain (TVI) according to ISO 12647-2 3. Print to pre-defined print densities and fine-tune print result by using gray balance patches K70 CMY70 K50 CMY50 K30 CMY30
  57. 57. Some examples on ink adjustments
  58. 58. Normal densityDensity too low Density too high
  59. 59. Normal dot gainDot gain too low Dot gain too high
  60. 60. Magenta dot gain too highTarget print conditions Magenta print density decreased
  61. 61. Sappi CM services
  62. 62. Sappi Offering in Colour Management 1. How to print on Sappi papers – Sappi Prepress Recommendations • Recommendations on correct printing conditions and use of correct ICC profiles with Sappi graphic papers 2. How to achieve high and consistent print quality – Colour management consultation including e.g. • Trainings • Creating customer specific ICC profiles • Printer auditing and consultation on standardised printing • Evaluating the whole CM workflow • Print quality evaluation of printed products (PQE – see next slide) • Optimising proofing
  63. 63. Colour management services - PQE • Colour quality check of printed product using established Print Quality Evaluation (PQE) method • checking colour consistency and quality of chosen printed product • recommendations based on results • print density levels • dot gain compensation • printability issues • standardised PQE reports with several languages • english, german, french, spanish, italian, polish, russian • Can be used as throw-in to introduce customers to our offering!
  64. 64. CM offering ”pyramid” Prepress datasheets, customer inquiries, International co-operation (TC130, ECI, Paperdam), own research PQE measurement cases (~10-20 / a) CM Projects (1-2 / a)
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