print quality

Print quality

Print quality

Light

Illumination conditions• inside / outside• sunny / cloudy• light bulb /

fluorescent light

Print quality• reproduction of colour• reproduction of details• visual impression of gloss• print defects

Reader• vision sets limits• likings differ• culture affects

Reproduction of colour and details

1 Reproduction of colour

• “how large colour space can be reproduced”

• “how well does the print match the original colours”

• affected by

• paper surface properties

• achievable print densities

• dot gain

• paper brightness and hue

• ink properties and trapping

2 Reproduction of details

• “how small details can be reproduced”

• “number of shades i.e. tone steps inside colour gamut”

• affected by

• screen ruling

• paper surface properties

• dot gain

-100

-50

0

50

100

-100 -50 0 50 100

a*

b*

INK DEMAND

INK DEMAND

Reproduction of color

Original

Coated paper's colour gamut

Uncoated paper's colour gamut

Correct dot gain Dot gain too high

-100

-50

0

50

100

-100 -50 0 50 100

a*

b*

0 %

5 %

10 %

15 %

20 %

0 % 10 % 20 % 30 % 40 % 50 % 60 % 70 % 80 % 90 % 100 %

Dot-%

Do

t g

ain

(T

VI)

CMY- PT1

CMY- PT3

Galerie Fine, >80gsm

Galerie Fine, 65-75 gsm

Colour gamuts - an example

-100

-50

0

50

100

-100 -50 0 50 100

Sheet-fed

Heatset

Newsprint

Gravure

Colour impression

1 Measured print density values = darkness

2 Measure lab-values = darkness and colour

white light print gloss = surface reflection of white light

print-trough

print density = coloured light

base paper

coating layer

ink layer

Ink demand

0

0,25

0,5

0,75

1

1,25

1,5

1,75

2

2,25

0 0,5 1 1,5 2 2,5 3

The amount of ink on paper, g/m²

Pri

nt

den

sity

• Roughness is the main limiting factor in colour gamut together with porosity

• Smoother paper can achieve higher print densities than rougher paper with same ink amount

• This means also higher colour gamut

Ink demand vs. roughness

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

0,8 1 1,2 1,4 1,6 1,8

Ink amount for print density of 1.4, g/m²

PP

S-r

ou

gh

ne

ss

Photo Inkjet papers

115 g Coated fine/MWC

80 g Coated fine/MWC

65g MWC/LWC

48-54g LWC

45-56g SC

matt

silk grades

• Ink demand is mostly controlled by roughness

• glossy coated grades

• And also by porosity

• uncoated and rougher papers

Dot gainDot gain is an increase in the diameter of the halftone dot

Limiting factor when choosing screen ruling

40% dot on plate 60% dot on paper 20% dot gain

Dot gain vs screen ruling - an example

0 %

5 %

10 %

15 %

20 %

25 %

30 %

0 % 20 % 40 % 60 % 80 % 100 %

0 %

5 %

10 %

15 %

20 %

25 %

30 %

0 % 20 % 40 % 60 % 80 % 100 %dot percentage

dot g

ain

52 l/cm 60 l/cm 70 l/cm 80 l/cm 90 l/cm

Dot gain

• Dot gain can be divided into

• mechanical dot gain (ink flows in xy-direction in the printing nip)

• nip pressure

• ink amount (paper roughness)

• absorption in xy-direction

• optical dot gain (light scattering)

• some of the light is trapped under the dot shadow

Dot gain - an example

Galerie Fine Gloss 115 g Galerie Brite 70 g Galerie Lite 45 g

Trapping

• Trapping is a measure how much ink printed on top of another ink transfers

• Important from when choosing ink sequence

• Influences to colour gamut through secondary colours

+ =

+=

+ =

Ideal situation

~70% of magenta is transferring

~70% of cyan is transferring

Trapping - an example (50x magnification)

+ =

Offs

et

Cyan 100% Magenta 100% Cyan + Magenta 200%

+ =

Gra

vure

Cyan 100% Magenta 100% Cyan + Magenta 200%

Print gloss

Very many printed products require high print gloss for visual appearance

0

10

20

30

40

50

60

70

80

90

100G

loss, %

Print gloss

Paper gloss

Formation of print gloss

• Macro-roughness (flock-size) causes poor ink transfer

• high print gloss variation and low print gloss

• Micro-roughness (fibre-size) affects to gloss level

uncoated

single coated

• Ink layer can cover optical roughness (pigment-size)

• high print gloss and low paper gloss

• Smooth and glossy paper gives highest print gloss

Formation of print gloss

double coated silk

double coated gloss

Effect of ink on print gloss• Printing ink has major influence on print gloss

• in this example over 15 units

70,0

75,0

80,0

85,0

90,0

95,0

0,0 0,5 1,0 1,5 2,0 2,5

Amount of ink on paper, g/m²

Print

glo

ss

10 commercial heatset inks printed on double coated gloss paper (laboratory)

Visual impression of gloss

• Our reader studies have shown that

• consumers don't pay attention to small gloss differencies• e.g. a reader study, where

• 30 consumers evaluated printed samples with different paper gloss (from 65% to 75%)

• approx. half of the consumers did not have any preference• ~15% preferred lower gloss paper• ~30% preferred higher gloss paper

• However print buyers still pay attention to gloss and it can have impact on the brand of the magazine in question

Print quality - a summary

• Print quality level according to purpose

• colour gamut• choice of paper, ink• printing method

• colour reproduction• understanding of the role of paper and ink on colour reproduction• using that understanding in prepress and printing

• gloss• has influnce on colour gamut• influences also through visual impression