Colour management aims to standardize colour reproduction across different devices and stages of the printing workflow. It involves using colour profiles and colour spaces to translate colours between devices and map colours that fall outside a device's gamut. Paper plays a key role in colour management by influencing colour gamut, dot gain, and luminance. Standardized printing as defined in ISO 12647-2 specifies paper groups, CMYK and RGB colour targets, dot gain targets, and tolerances to help ensure colour consistency. Sappi provides services like prepress recommendations, colour management consultations, print quality evaluations, and trainings to help customers achieve high and consistent print quality.
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. World of colour - technical
• Light is electromagnetic radiation
400 nm 700 nm
pm nm um cm m
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. 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
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. ∆E – an example
∆E = 1
∆E = 2
∆E = 3
∆E = 4
∆E = 5
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. 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. 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. 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
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. ICC output profiles (press profiles)
• ICC output profiles
have two functions
1. To separate images for
printing
2. To simulate printing in
proofing
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
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
28. History of proofing
Flat-bed proofing
Analog proofers
1st generation of digital
proofers
Modern digital proofers
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. 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
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. 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
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. 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. • 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. 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. 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
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. 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. 1. Paper groups 2. Lab targets for CMYK, RGB
3. Dot gain targets
4. Tolerances for Lab, dot gain
ISO 12647-2:2004
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. 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. 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. 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. 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. How to control dot gain in CM workflow
dot gain is
influenced=
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
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. 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. 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)
