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

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

Sept 2010iarigai Montreal Luc LANAT 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 clarify1/2

• 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 clarify2/2

• 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 lightResults 1/3

• 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 sc ale on right.

40

50

60

70

80

90

100

110

Offset

News

52 gs

m

Impr

oved

New

s 52 g

smSC A

56 gs

mSC A

56 g

sm

SC A 5

6 gsm

LWC 57

gsm

LWC 57

gsm

Impr

oved

New

s 52

gsm

Impr

ove d N

ews 5

2 gsm

SC A+ 56

gsm

LWC 54

gsm

SC A++

57 gsm

SCA++ 57

gsm

LWC 57

gsm

SC A +

+ 51 gs

mLW

C 70 gs

m

MWC 7

0 gsm

MWC 8

0 gsm

WF S

ilk 11

5 gsm

0102030405060708090100

Fluorescence, D65/10° D65-Brightness CIE-Whiteness, C/2°


1. Whiteness panel, indoor but Nordic light Resultats 2/3

• 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

50

60

70

80

90

100

110

Offset N

ews 5

2 gsm

Impr

oved

News 52

gsm

SC A 56

gsm

SC A 56

gsm

SC A 56

gsm

LWC 5

7 gsm

LWC 5

7 gsm

Impr

o ved N

ews 5

2 gsm

Impr

o ved N

ews 5

2 gsm

SC A+

56 gs

mLW

C 54 g

sm

SC A++

57 g

sm

SCA++ 5

7 gsm

LWC 5

7 gsm

SC A +

+ 51 g

smLW

C 70 g

sm

MWC 70

gsm

MWC 80

gsm

WF S

ilk 11

5 gsm

0102030405060708090100



1. Whiteness panel, indoor but Nordic lightResultats 3/3

• 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

50

60

70

80

90

100

110

Offset N

ews 5

2 gsm

Impr

oved

News 52

gsm

SC A 56

gsm

SC A 56

gsm

SC A 56

gsm

LWC 5

7 gsm

LWC 5

7 gsm

Impr

o ved N

ews 5

2 gsm

Impr

o ved N

ews 5

2 gsm

SC A+

56 gs

mLW

C 54 g

sm

SC A++

57 g

sm

SCA++ 5

7 gsm

LWC 5

7 gsm

SC A +

+ 51 g

smLW

C 70 g

sm

MWC 70

gsm

MWC 80

gsm

WF S

ilk 11

5 gsm

0102030405060708090100



-120

-80

40

120

-120 -80 120

a*

b*

AB

FE

DC

-120

-80

40

120

-120 -80 120

-120

-80

40

120

-120 -80 120

a*

b*

AB

FE

DC

Colour Management-Colour Gamut calculationReminder 1/4

Schläpfer (2000)

C – offset on coated

B – gravure on coated

F – newspaper (CSWO)

A – Küppers 7-colour

Gamut categories for printing processes

Schläpfer (2000)



• 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

1

22

n

*

n

*

n

*baSumC

• NOTE :– 50 units in Chroma sum to identify different categories.

– L* coordinate not included in calculation.



• 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.


Colour Management-Colour Gamut calculationa*b* coordinates of rotogravure prints Reminder 4/4

-60

-40

-20

0

20

40

60

80

100

-80 -60 -40 -20 0 20 40 60 80

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 GamutMethods

• 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.


2. HSWO printing. 12647-2 and Colour GamutResults 1/5

-20

-15

-10

-5

0

5

10

15

20

-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


Paper Black

Full circle = tolerances of ISO 12647-2, center on target.Dotted circle = tolerances of ISO 12647-2, center on average of all papers.



-20

-15

-10

-5

0

5

10

15

20

50 55 60 65 70 75 80 85 90


-70

-65

-60

-55

-50

-45

-40

-35

-30

-60 -55 -50 -45 -40 -35 -30 -25 -20


Cyan Magenta




30

35

40

45

50

55

60

65

70

50 55 60 65 70 75 80 85 90


70

75

80

85

90

95

100

105

110

-20 -15 -10 -5 0 5 10 15


Yellow Red (M+Y)




-70

-65

-60

-55

-50

-45

-40

-35

-30

5 10 15 20 25 30 35 40


5

10

15

20

25

30

35

40

45

-85 -80 -75 -70 -65 -60 -55 -50 -45


Green (C+Y)Blue (C+M)



2. HSWO printing. 12647-2 and Colour GamutComments

• 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.



300

320

340

360

380

400

420

440

460

480

500

MW

C G

loss

Pap

er B

MW

C G

loss

Pap

er A

2

MW

C G

loss

Pap

er A

1

MW

C G

loss

Pap

er C

LW

C+

Glo

ss P

aper

E

MW

C G

loss

Pap

er D

LW

C+

Glo

ss P

aper

A3

LW

C G

loss

Pap

er F

MW

C G

loss

Pap

er D

MW

C G

loss

Pap

er B

MW

C G

loss

Pap

er A

1

LW

C+

Glo

ss P

aper

A2

MW

C G

loss

Pap

er C

LW

C+

Glo

ss P

aper

E

MW

C G

loss

Pap

er A

1

MW

C G

loss

Pap

er D

MW

C G

loss

Pap

er C

WF

Glo

ss P

aper

A0

WF

Glo

ss P

aper

B

WF

Silk

Pap

er A

0

MW

C S

ilk P

aper

A1

MW

C S

ilk P

aper

C

WF

Mat

t Pap

er B

300

320

340

360

380

400

420

440

460

480

500

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 !


2. HSWO printing. 12647-2 and Colour GamutComments

• 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 millMethods

• 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.

90/-0,8/2,60,80,744857LWC Gloss

91/0,1/-40,80,975560LWC Silkhigh

brightness

L*/a*/b* D65

BulkPPS roughness

Glossgsm


3. Gravure printing LWC grades - same millResults

C* sum close for both papers (382 versus 376)

-120

-80

-40

0

40

80

120

-120 -80 -40 0 40 80 120CIELAB-a*

LWC Silk high brightness LWC Gloss

-40

-30

-20

-10

0

10

20

30

40

-40 -30 -20 -10 0 10 20 30 40CIELAB-a*

LWC Silk high bright.LWC Gloss

40% tone100% tone

C* sum exactly equivalent (146 versus 146)

b* shifted 5 units (D50)(b* difference 6,6 with D65)


3. Gravure printing LWC grades - same millComments

• 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.


StandardizationReminder on ISO 12647 1-7 (8)

• Ex: 12647-2.

– Is limited to 5 paper types.

– Gives AIM values for each printedcolour.

• Unprinted Paper shades aim values.

• Standard should be REVIEWED.


NWI 15339 Process Agnostic approach

Colour Gamut with relevant tolerancesdepending of printing method and paper type.

Need for Research support to developStandardization.


NWI 15397Communication of Optical and Surface Properties of printing substrates


NWI 15397Communication 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 settingsBack 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 DataBack to real life 2/3


Stora Enso FAN 2009 Colour L*, a*, b* D 50Back to real life 3/3


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 LANATStora Enso Publication Paper, Corbehem mill, [email protected]

Anna NICANDERStora Enso Research Karlstad, [email protected]


Presentations & Public Speaking

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