print quality
DESCRIPTION
Print QualityTRANSCRIPT
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
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