Iarigai lanat communication on visual perception and colour management montreal presentation 2010

Visual Perception and Colour Management
Luc LANAT, Anna NICANDER iarigai Montreal Sept. 2010

iarigai Montreal Luc LANAT Sept 2010 2
Summary
• Why are we here ? Misunderstandings to clarify.
• Study 1. Whiteness panel ranking of European commercial papers, indoor but
Nordic light.
• Study 2. ISO12647-2 targets and evaluation of Colour Gamut at full tones in
Heat Set Web Offset MWC papers from European market 2009.
• Study 3. Gravure trial 2010 at industrial printer to compare LWC and LWC high
brightness from same mill.
• Link with Standardization and Conclusions.

Why are we here ?
“ Communication within the value chain of paper-print:
visual perception and colour management on commercial publication paper
grades.”
• Printed media efforts must concentrate on what they do best: offering emotions.
• Emotions and quality images are linked.
• We need:
– Optical paper measurements to match visual perception with human eye in
usual home-office conditions.
– Quantify paper performance when evaluating colour coordinates of the
CMY-RGB hexagon.
– Encourage further standardization developments.

Misunderstandings to clarify
1/2
• Misunderstandings due to differences between printing equipments and
papermaking equipments.
– Geometry 45°/0°or 0°/45°versus papermakers d/0°.
– Calibration routines existing in papermaking, not in printing.
• Misunderstandings due the differences in lighting conditions between
papermakers and printers.
– Papermakers use D65 illuminant mostly Xenon light sources.
– Printers use D50 illuminant for historical reasons (Jordan, 2006).
– CIE illuminant, ID65 (indoor D65), Nordic daylight behind a window, adds
confusion.
– WCIE C2°close to WCIE ID 65 ??

Misunderstandings to clarify
2/2
• Misunderstandings between colour management prepress specifications and
visual perception of white paper colour.
– White point of paper is needed as a zero point for colour management
software and characterization data.
– The visual aspect of white paper is a different concept than paper colour
measurement needed for colour management settings.
• Misunderstandings on printing relevant properties.
– Which paper properties are relevant for paper during printing?
• Misunderstandings motivated by different interests between stakeholders.
– Value-chain not technically talking much.

Methodology and equipments
• Elrepho spherical spectrophotometer (d/0°), availab le in paper industry.
– Routines are available to measure Colour L*, a*, b* D50, with the UV
calibration of C illuminant. See ISO 5631-3.
• i-one X-Rite angular spectrophotomer (45°/0°) used in graphic industry for
printing evaluations.
• Printing trials HSWO and Gravure.
– Most parameters kept constant, and concentrated on paper changes.
– Target ink densities typical for coated and uncoated papers.
– Inks were industrial inks.
– HSWO trials printed at KCL pilot plant in Finland.
– Gravure trials at industrial printer in France.

1. Whiteness panel, indoor but Nordic light
Methods
• Visual panel for paper whiteness perception.
• 12 experienced people to rank papers from Improved News up to WFC (Wood
Free Coated)
• Test operated in Falun mid-Sweden indoor but behind a window under noon
overcast Nordic daylight.
• Compare ranking with optical laboratory properties :
– Brightness D65, C Brightness, Whiteness, Colour L*a*b*

1. Whiteness panel indoor, but Nordic light
Results 1/3
SC A+ 56 gsm
LWC 54 gsm
SC A ++ 51 gsm
WF Silk 115 gsm
MWC 80 gsm
100
90
80
70
60
50
40
30
20
10
• Visual
Whiteness
perception
under indoor
conditions
but Nordic
overcast
daylight,
papers in x-axis
in order
of visual
ranking.
Whiteness-Brightness scale on left, Fluorescence scale on right.
110
100
90
80
70
60
50
40
SC A 56 gsm
Improved News 52 gsm
SC A 56 gsm
Offset News 52 gsm
SC A 56 gsm
LWC 57 gsm
LWC 57 gsm
SC A++ 57 gsm
SCA++ 57 gsm
LWC 57 gsm
LWC 70 gsm
MWC 70 gsm
0
Fluorescence, D65/10° D65-Brightness CIE-Whiteness, C/2°

Resultats 2/3
110
100
90
80
70
60
50
SC A 56 gsm
LWC 57 gsm
SC A+ 56 gsm
LWC 54 gsm
SC A ++ 51 gsm
MWC 80 gsm
100
90
80
70
60
50
40
30
20
10
• Whiteness C values
from 40 to 110.
• D65 Brightness values
from 60 to 95.
– Whiteness is thus
more distinctive.
• Papers at same
Brightness D65 do show
differences when
measured with
Whiteness C.
– Whiteness C more in
accordance with visual
ranking. Preferred !
40
Offset News 52 gsm
SC A 56 gsm
SC A 56 gsm
LWC 57 gsm
SC A++ 57 gsm
SCA++ 57 gsm
LWC 57 gsm
LWC 70 gsm
MWC 70 gsm
WF Silk 115 gsm
0

Resultats 3/3
110
100
90
80
70
60
50
SC A 56 gsm
LWC 57 gsm
SC A+ 56 gsm
LWC 54 gsm
SC A ++ 51 gsm
MWC 80 gsm
100
90
80
70
60
50
40
30
20
10
• Whiteness values > 60:
– Whiteness C closer
match than D65
Brightness.
• Whiteness values < 60:
– Shade and
Fluorescence
dominates.
• Visual evaluations differ
due to shade at lower
whiteness.
• Whiteness calculation
formula integrates
shade.
– b* shade and L* are
most influent on
Whiteness.
40
Offset News 52 gsm
SC A 56 gsm
SC A 56 gsm
LWC 57 gsm
SC A++ 57 gsm
SCA++ 57 gsm
LWC 57 gsm
LWC 70 gsm
MWC 70 gsm
WF Silk 115 gsm
0

Colour Management-Colour Gamut calculation
C
-120 -80 120
A – Küppers 7-colour
B – gravure on coated
120
40
-80
-120
a*
b*
A
B
F
E
D
Reminder 1/4
Schläpfer (2000)
C – offset on coated
F – newspaper
(CSWO)
Gamut categories for
printing processes
Schläpfer (2000)

Reminder 2/4
• Larger colour gamut, or colour range commonly accepted as better print quality.
• Kurt Schläpfer (2000) suggested to evaluate the chroma (saturation) values of
primary colours - Cyan C, Magenta M, Yellow Y -and the secondary colours -
Red (M+Y), Green (C+Y) and Blue (C+M).
• One single number, the gamut area in the a* b*-plan : Chroma sum (C* Sum)
with 6 primary and secondary colours.
6
Σ( ) ( ) =
2 2
= +
* C Sum a b
1
n
*
n
*
n
• NOTE :
– 50 units in Chroma sum to identify different categories.
– L* coordinate not included in calculation.

Reminder 3/4
• Internal study Stora Enso Press Selection grades printed in rotogravure.
• Results were in line with usual paper classification.
• Ranking from low to high Colour Gamut in a* and b* plane:
– Improved News 52 gsm, White Improved News 55 gsm, SC B 56, SC A 56
gsm, SC A+ 56 gsm, SC A ++ 54 gsm, LWC 54 gsm, LWC 57 gsm, LWC +
70 gsm.
– Close to L* coordinate ranking, thus study further the a* and b* plane, as
an approach to colour gamut evaluation.

a*b* coordinates of rotogravure prints Reminder 4/4
100
80
60
40
20
0
-80 -60 -40 -20 0 20 40 60 80
-20
-40
-60
Kv ExoPress 52
Su SilvaPress 55
Lg EnviPress 56
MX EnviPress 56
Kv PubliPress 56
Mx PubliPress 56
Su MagniPress Bulky 56
Re InnoPress 54
Ka Neo G 57 (54?)
Co Neo G 57
Co Terra G 70

2. HSWO printing. 12647-2 and Colour Gamut
Methods
• Printing HSWO MWC papers from 70 to 115 gsm European market.
– Position the colour gamut variations versus ISO-ECI-FOGRA targets
described in characterization data.
– Evaluate colour gamut to rank papers with possible links to paper
properties.
• Pilot plant under consistent conditions. Web 130°c onstant.
– Target densities: Black 1,70 / Cyan 1,50 (+/-0,05) / Magenta 1,30 / Yellow
1,20 and kept constant for all grades.
– Target densities were not optimised to reach CIELAB values for primary
and secondary colours as specified in ISO 12647-2.

Results 1/5
Full circle = tolerances of ISO 12647-2, center on target.
Dotted circle = tolerances of ISO 12647-2, center on average of all papers.
Paper Black
20
15
10
5
0
-5
-10
-15
-20
All papers ISO12647-2 (1&2)
-20 -15 -10 -5 0 5 10 15 20
20
15
10
5
0
-5
-10
-15
-20
-20 -15 -10 -5 0 5 10 15 20

Results 2/5
Cyan Magenta
20
15
10
5
0
-5
-10
-15
-20
50 55 60 65 70 75 80 85 90
-30
-35
-40
-45
-50
-55
-60
-65
-70
-60 -55 -50 -45 -40 -35 -30 -25 -20

Results 3/5
Yellow Red (M+Y)
70
65
60
55
50
45
40
35
30
50 55 60 65 70 75 80 85 90
110
105
100
95
90
85
80
75
70
-20 -15 -10 -5 0 5 10 15

Results 4/5
-30
-35
-40
-45
-50
-55
-60
-65
-70
5 10 15 20 25 30 35 40
Green (C+Y)
45
40
35
30
25
20
15
10
5
-85 -80 -75 -70 -65 -60 -55 -50 -45
Blue (C+M)

Comments
• Variation tolerances allowed in 12647-2 are reached. They are rather wide and
even allow papers ranging from LWC 70 gsm up to WF 115 gsm, Silk and
Gloss to be within the tolerances allowed by the standard.
• ISO targets (see figure 2a tests on blank Paper) differ from average of papers
tested. So, there is a clear need for evaluation of paper white point as a colour
for best colour management calculations.
• Schläpfer (2000), mentions a 50 points difference as being relevant to
differentiate printing processes. It seems that the calculation may still give too
much importance to shade.

Results 5/5
LWC Gloss Paper F
LWC+ Gloss Paper A2
MWC Gloss Paper A1
MWC Gloss Paper C
WF Gloss Paper A0
MWC Gloss Paper C
WF Silk Paper A0
MWC Silk Paper A1
500
480
460
440
420
400
380
360
340
320
500
480
460
440
420
400
380
360
340
320
300
LWC+ Gloss Paper E
MWC Gloss Paper A2
MWC Gloss Paper B
LWC+ Gloss Paper A3
MWC Gloss Paper A1
MWC Gloss Paper C
MWC Gloss Paper D
MWC Gloss Paper D
MWC Gloss Paper B
LWC+ Gloss Paper E
MWC Gloss Paper A1
MWC Gloss Paper D
WF Gloss Paper B
MWC Silk Paper C
WF Matt Paper B
300
C* sum at 100% tone (left scale) Average
70 gsm 80 gsm 115 gsm Gloss 115 gsm
• Tendency : higher grammage better C* sum. Expected !
• 115 gsm Gloss vs Silk, Silk less smooth thus lower C* sum. Expected !
• C* sum difference within paper types negligible. Only between paper types !

Comments
• Correlation with Colour Gamut vs paper properties.
– Most relevant were Gloss, PPS roughness, b* shade, but no clear
conclusion.
– PPS was best to forecast the potential Colour Gamut. Primitive but
available !

3. Gravure printing LWC grades - same mill
Methods
• Compare 2 papers with surface and colour difference :
• LWC Silk versus Gloss, difference in gloss and touch and feel
properties.
• LWC high and normal Brightness.
• ECI 2002 colour patches (more than 1600) were printed.
L*/a*/b*
D65
PPS Bulk
roughness
gsm Gloss
LWC Silk 60 55 0,97 0,8 91/0,1/-4
high
brightness
LWC 57 48 0,74 0,8 90/-0,8/2,6
Gloss

Results
120
80
40
0
-40
-80
100% tone 40% tone
C* sum close for both papers
(382 versus 376)
40
30
20
10
0
-10
-20
-30
-120
-120 -80 -40 0 40 80 120
CIELAB-a*
LWC Silk high brightness LWC Gloss
-40
-40 -30 -20 -10 0 10 20 30 40
CIELAB-a*
LWC Silk high bright.
LWC Gloss
C* sum exactly equivalent
(146 versus 146)
b* shifted 5 units (D50)
(b* difference 6,6 with D65)

Comments
• White point settings will influence colour qualities !
• But also :
– Colour gamut is a non-symmetric 3D volume space from black CMYK
(overprinting) up to white end (paper whiteness).
– Visually, at higher L* values, as per our experience :
• reddish paper shade giving warm colour to white human skin.
• bluish paper shade giving "sick" colour to the human face.

Summary of Conclusions
• Paper whiteness depends of lighting conditions.
– Use Whiteness C illuminant 2°observer for visual pe rception.
– D65 Brightness 10°, linked to commercial decisions , useful for papermaking process
monitoring, is also mentioned in most Technical Data Sheets.
– Introducing Indoor and Outdoor Whiteness with reviewed calculations will help.
• 12647 paper colour targets are misleading.
– Markets do change and are free.
– Determination of white point of paper is a must.
• Papermakers agreed:
– To recommend best publicly available paper profiles and characterization data.
– To make available paper Colour L*, a*, b* D50 (or D65) for printers when needed.
• Achievable Colour Gamut depends of printing process and printing conditions.
– Does not depend of paper shade only.
– Depends on surface, then to L* values and then to shade (or fluorescence thus).
– 10 to 15 printing process settings are needed corresponding to 10 to 15 paper types.
– Further work is needed to agree on standardized and reproducible methodologies.

Standardization
Reminder on ISO 12647 1-7 (8)
• Ex: 12647-2.
– Is limited to 5 paper types.
– Gives AIM values for each printed
colour.
• Unprinted Paper shades aim values.
• Standard should be REVIEWED.

NWI 15339 Process Agnostic approach
Colour Gamut with relevant tolerances
depending of printing method and
paper type.
Need for Research support to develop
Standardization.

NWI 15397
Communication of Optical and Surface Properties of printing substrates

NWI 15397
Communication of Optical and Surface Properties of printing substrates
• Grammage. Bulk or specific
volume. Opacity.
• Roughness.
– PPS (Parker-print Surf) for
coated grade and Gravure
– Bendtsen for Mat, Silk or
Uncoated grade.
• Gloss. (or Gloss, Silk, Matt
for Proof substrates).
• For visual evaluation on unprinted paper.
– Brightness or Whiteness.
• For evaluation of paper white point under D50
illuminant.
– Colour as per L*, a*, b* D50 (printing conditions).
• For evaluation of unprinted substrate under D65
illuminant.
– Colour as per L*, a*, b* D65 (outdoor conditions).
• Prepress Colour Management.
– Deviations expected due to UV content of light.
– Public characterization data recommendations.

ISO Standardization running topics Sept. 2010
• TC 130 Graphic Technology Sao Paulo October 2010.
– 12647 updates ?
– NWI 15397 Communication of printing substrates prop.
– NWI 15339. Digital printing.
– NWI 15311 series. Process Agnostic approach.
– TF1 Carbon Footprint/LCA ? working group.
• TC 6 Pulp and Paper Paris May 2011.
• ID 65 illuminant. No need BUT verify WCIE versus C.
• D 50 light source calibration in UV.
• WCIE D 65 formula modified Indoor, Outdoor.

Paper White point for prepress settings
Back to real life 1/3
• Determine colour of unprinted paper using ISO 5631-3 (D 50, papermakers, UV
calibrated with C illuminant reference samples)
• Calibration routines are widely available and in operation worldwide. This can
be done with either papermaker's equipments or printer's equipments.
• Printing equipments differ from equipments used within paper mills, meant for
white paper process control.
• But results of correctly calibrated equipments are close, if calibration is corect,
UV settings in particular. Geometry has little influence (Edström, NPPRJ 2010)

Stora Enso FAN Characterization Data

Stora Enso FAN 2009 Colour L*, a*, b* D 50

Bibliography
• Whiteness, Fluorescence issues.
o Coppel L, Lindberg S, Rydefalk, S. - Innventia.
o Puebla, C. Axiphos.
• Colour Gamut.
o Schläpfer, K.
• Illuminants.
o Jordan, B, O’Neill, M.A.
o Bristow, A.
o Gombos, Katalin. Color Research and application. ID illuminants.
• TC 130 Standardization related topics.
o Chung, R. How to overcome OBA. ISO Communication Sao
Paulo.
o Mc Dowell, D. Process Control, and Color Management.

Paperdam Working Group on Standardization
• Active in TC 130 Graphic Technology.
• 9/10 biggest European papermakers. See www.paperdam.org.
• Paper types to be worked out with TC 6 (10 or 15) types).
UPM
Stora Enso
M-real
Norske Skog
Burgo Group
Sappi
Myllykoski
Holmen
Mondi
Lecta Group
Coated mech
SC
Newsprint
WF coated
WF uncoated

Our message in 1 slide
• We promote Whiteness concept for paper perception.
• We suggest that Colour is only useful for printers settings.
• We calculated Colour Gamut of market magazine papers.
– We show that using C* Sum calculation from litterature can be used only to
identify paper types.
– It is suggested that PPS roughness, although primitive, is more distinctive
for paper types than shade references.
• We suggest to use paper white point for best prepress colour management
settings and not the existing ISO standard.

Thank you
Luc LANAT
Stora Enso Publication Paper, Corbehem mill, France
luc.lanat@storaenso.com
Anna NICANDER
Stora Enso Research Karlstad, Sweden
anna.nicander@storaenso.com

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