Image quality criteria for digital printing

PTS Paper and Imaging Symposium, 2014
Image quality
criteria for digital
printing
Dr. Andreas Kraushaar | [email protected]
1
PTS Paper and Imaging Symposium, 2014
Agenda
1.Challenges in image quality assessment
2.Categorisation of image quality attributes
3.Image quality from market point of view
4.Image quality attributes review
5.Summary & Outlook
Dr. Andreas Kraushaar | [email protected]
2
PTS Paper and Imaging Symposium, 2014
1. Challenges for image quality assessment
„When you can measure what you are speaking
about and express it in numbers, you know
something about it“
Lord W. T. Kelvin, Lecture to the Institution of Civil
engineers, London, 3 May 1883
"All colors must be evaluated numerically".
A. Kling, Keynote, Color Management Conference
We need objective measures (if possible based on agreed upon [ISO] standards)
„The ultimate test of any colour reproduction is the
opinion of the person who views it. But opinions differ...“
R. W. G. Hunt. In: The reproduction of color
We need to focus on use cases which provides
(full) reference (contrary to no reference)
Dr. Andreas Kraushaar | [email protected]
3
PTS Paper and Imaging Symposium, 2014
2. Categorization of image quality attributes
System
Colour
¬ Bulltet 1
reproduction
Resolution
Permanence
Uniformity
Artefacts
Functional
performance
¬ Productivity
¬ on site reliability
¬ etc.
Health, Safety,
Environment
arbitrary but useful
Dr. Andreas Kraushaar | [email protected]
4
PTS Paper and Imaging Symposium, 2014
2. "absolute" and "relative" quality
Image Quality
use case
dependent criteria
Uniformity, Detail sharpness,
Artefacts
Dr. Andreas Kraushaar | [email protected]
use case
independent
criteria
Colour: Level of visual
closeness between a reference
and a reproduction
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PTS Paper and Imaging Symposium, 2014
Electronic Imaging Symposium
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D R A NDREAS K RAUSHA AR
2. Categorization of image quality attributes
For more than 20 years, the Electronic
Imaging Symposium (abbr. EI) has been
the one international conference where
papers on all aspects of electronic imaging, from image sensing to display and
hardcopy, are presented.
Topics include, but are not limited to
stereoscopic displays and applications,
sensors, digital photography, colour
hardcopy, human vision, image process-
a single overall quality judgement is
one of the utmost questions. In almost
all cases the famous Image Quality Circle was used to illustrate the pertinent
questions. The Image Quality Circle,
developed by Peter G. Engeldrum, is a
process for managing the image quality of imaging products. It consists of
four elements illustrated by the rounded
rectangles in Figure 1 namely “Technol-
Image quality attributes for system design versus use case description
Printe
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sent to
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report
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site (w
then b
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Fogra
2013
Fig. 1: Image Quality Circle according to P. Engeldrum.
ogy Variables”, “Physical Image Parameters”, “Customer Perceptions” and
“Customer Image Quality Rating”. The
double arrows of the connection links
indicate that the process works in both
directions. You can use the Image Quality Circle in both clockwise and counter
clockwise directions.
Based on the overall image quality (top)
there is a connection to both the technological variables (right) 6
and the customer perceptions. The technological
Fogra focus:
Description of typical (“standardizable”) reference applications (uses cases)
Dr. Andreas Kraushaar | [email protected]
The papers presented in the area of
image quality clearly showed that there
is still a long way to go. Knowing how
to combine the perceived attributes to
www
fogra-r
Background: © visualtouch at www.photocase.com
ing and compression, image quality,
image security, image analysis, printing,
and multimedia imaging systems. The
following lines reflect the summary of
the author who selected the important
papers in the field of human vision and
colour imaging.
PTS Paper and Imaging Symposium, 2014
2. Categorization of image quality attributes
“Singlenumerities” won’t work
Dr. Andreas Kraushaar | [email protected]
7
PTS Paper and Imaging Symposium, 2014
3. Typical market segments
Typical segmentation
✔
Large Format
Printing
✔
Small Format
Printing
LFP-applications
¬
¬
¬
¬
¬
¬
¬
¬
¬
¬
¬
¬
¬
¬
¬
¬
¬
¬
¬
Dr. Andreas Kraushaar | [email protected]
Digital Fine Art!
Digital Photography!
Decoration!
Promo displays!
POP/POS!
Advertising posters!
Displays!
Packaging!
Exhibition graphics!
Event graphics!
Information signs!
Personalized signs!
Traffic signs!
Banners & building covers!
Billboards!
Transit signage!
Vehicle wraps!
Fleet graphics!
Truck curtains
How to cluster?
¬ Indoor & outdoor!
¬ Viewing distance
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PTS Paper and Imaging Symposium, 2014
3. Concept of ISO 15311-3
Graphic Technology — Requirements for printed matter utilizing digital printing
technologies for the commercial and industrial production — Part 3: Large Format
Signage Printing
Fine Art, Digital Photography,!
Interior Decoration, Small POP/POS!
Displays and Signs, Decoration up!
to 1x1,5 m
POP/POS Displays, Trade Show!
Graphics, General Purpose!
Signage, Citylight, Advertising!
Posters from 0,75x1 to 1,5x3 m
Backlit, Unipol, Wall Murals, Large!
Trade Show Graphics, Transit,!
Scroller, Transportation/Bus!
Shelters, Vehicle Wraps from 2,5x3!
to 4x12 m
Billboard, Big banners & building!
covers, No standard format, but!
usually varies up from 50 m2!
(biggest found was over 1600 m2)
Dr. Andreas Kraushaar | [email protected]
9
PTS Paper and Imaging Symposium, 2014
4. Colour: Number of discernible tonal steps
Dr. Andreas Kraushaar | [email protected]
10
PTS Paper and Imaging Symposium, 2014
4. Homogeneity: What do we mean?
Homogeneity (uniformity)
subjective impression of colour uniformity across
a large image that is intended to have a uniform colour.
Refers to all types of colour variation:
¬ lightness, hue, saturation
¬ derivatives of these can be measured separately or in combination
Variation geometry:
¬ 1D, 2D, periodic, aperiodic, localized, large-scale, and small-scale
variation, separately or in combination such as streaks, bands, gradients,
mottle, graininess and moiré.
Rasmussen, Tent-pole spatial defect pooling for prediction of subjective quality assessment of streaks and bands in color printing
Dr. Andreas Kraushaar | [email protected]
11
PTS Paper and Imaging Symposium, 2014
4. Homogeneity: One word about graininess
Text
Rank order experiment
¬ Bulltet 1
test charts
different levels of graininess
¬ We propose three default
¬
Dr. Andreas Kraushaar | [email protected]
viewing distances (50 cm
[reading], 100 cm [POP] and
1,5 m [Large Format]
Simple evaluation of standard
test chart with a standard
scanner
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PTS Paper and Imaging Symposium, 2014
4. Homogeneity: Macroscopic Mottle
M-Score
1. Scan
2. Preparation
3. Summing up & Normalise
CIEL*
4. Calculating M-Score
CIEb*
CIE L,a,b profile long/short site
Dr. Andreas Kraushaar | [email protected]
13
PTS Paper and Imaging Symposium, 2014
4. Homogeneity: Macroscopic Mottle
M-Score
Meaning
M-Score
Comments
≥ 95
Perfect
Inkjetprint on proofing substrate showing
no visible inhomogeneities
> 80
Very Good
Print with slightly visible inhomogeneities
(e.g. some Mottling). No visible stripes.
> 70
Good
Print with visible inhomogeneities (Mottling)
but almost no visible stripes.
> 60
Satisfactory
Mottling and stripes visible. Is still accepted
by most observers.
> 50
Adequate
Print with clearly visible mottling and/or
stripes. Acceptance is highly dependent on
the printed image.
< 50
Poor (But
sellable)
Clearly visible mottling and stripes. Not
accepted as high quality print
ISO/TS 18621-21
Dr. Andreas Kraushaar | [email protected]
14
PTS Paper and Imaging Symposium, 2014
4. Perceptual resolution - concept
Testchart-Design
Perceptual
Resolution Correlate
Correct Interpretation (Driving) - “RIP-resolution”
Resolution attributes
¬
¬
¬
¬
¬
¬
Printing
- “Imaging-resolution”
Print Inspection
(visually | measurement
wise)
native addressability
effective addressability
edge blurriness
edge raggedness
MTF
more to come
Dr. Andreas Kraushaar | [email protected]
15
PTS Paper and Imaging Symposium, 2014
4. Perceptual resolution - ragged & blurry
Raggedness
Blurriness
Scan
Dr. Andreas Kraushaar | [email protected]
16
PTS Paper and Imaging Symposium, 2014
4. Perceptual resolution: L-Score
2. PreProc.
7.7
4.6
3x3 4x4
1x1 2x2
1.7
1.0
1
2
3
0.81
4
per Millim
1.04
5
1.35
6
1.74
7
Ver. 1.8
Resolution
1.7
1.0
1
0.81
2
1.04
3
1.35
4
1.74
5
2.24
6
2.91
7
3.76
8
4.85
9
B
C
D
E
F
G
H
J
10
6.25
D
E
Contrast-Resolution Test Target
B
C
F
G
H
J
K
Ver. 1.8
Output device: Acrobat Distiller 10.1.3 Addressability: 150 spi, 169.3 /spot
10
A
9
4.85
A
0.63
6.25
8
3.76
4. Norm. Cross
% Contrast, Log step increments
correlation
Spatial 7.7
Filtering4.6
59.9
35.9 21.5 3.12.9
2.8
K
0000110
100
Contrast-Resolution Test Target
Ver. 1.8
Output device: Acrobat Distiller 10.1.3 Addressability: 150 spi, 169.3 /spot
Resolution, Line Pairs per Millimeter, Log steps
irs per Millimeter, Log steps
100
0.63
0.81
1.04
5. Tresholding
% Contrast, Log step increments
35.9 21.5 12.9 7.7
4.6
2.8
1x1 2x2 3x3 4x4
1.7
1.0
1
0.81
2
1.04
3
1.35
4
1.74
5
2.24
6
2.91
7
3.76
8
4.85
9
6.25
10
1.04
2
3
1.35
4
1.74
5
2.24
6
2.91
7
1.74
3.76
4.85
6.25
A
B
C
D
E
8
C
D
E
F
G
H
J
K
9
L − Score = CDF(CCT0.5 + 4,45,12) − 5
10
F
G
H
J
Dr. Andreas Kraushaar | [email protected]
2.24
B
1
1.35
0.81
Licensed to: Use only at Rochester Institute of Technology
0.63
59.9
1.0
© Franz Sigg, 2005
Resolution, Line Pairs per Millimeter, Log steps
100
1x1 2x2 3x3 4x4
1.7
6. Calculation of LScore
Ver. 1.8
Output device: Acrobat Distiller 10.1.3 Addressability: 150 spi, 169.3 /spot
% Contrast, Log step increments
35.9 21.5 12.9 7.7
4.6
2.8
0.63
A
Contrast-Resolution Test Target
59.9
Licensed to: Use only at Rochester Institute of Technology
% Contrast, Log step increments
35.9 21.5 12.9 7.7
4.6
2.8
2.91
© Franz Sigg, 2005
59.9
Licensed to: Use only at Rochester Institute of Technology
Resolution, Line Pairs per Millimeter, Log steps
100
1x1 2x2 3x3 4x4
© Franz Sigg, 2005
Contrast-Resolution Test Target
, Line Pairs
2.24
Output device: Acrobat Distiller 10.1.3 Addressability: 150 spi, 169.3 /spot
of Technology
ast,
% Contr
12.9
35.9 21.5
Institute
59.9
0.63
eter, Log
steps
100
at Rochester
Output device
only
to: Use
1.8
Target Ver.
169.3 /spot
: 150 spi,
on Test
Addressability
-Resoluti
Contrast : Acrobat Distiller 10.1.3
increments
2.8
Log step
Licensed
Reference
(Testform)
2005
1. Scan
© Franz Sigg,
Print
K
17
PTS Paper and Imaging Symposium, 2014
4. Perceptual resolution: L-Score
L-Score
Meaning
≥ 90
Perfect
> 80
Very Good
> 60
Good
> 40
Satisfactory
>= 20
Adequate
< 20
Poor (But
sellable)
Dr. Andreas Kraushaar | [email protected]
ISO/TS 18621-31
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PTS Paper and Imaging Symposium, 2014
5. Summary
¬ Image quality is and will be an active field of research
¬ Different needs for system engineering and application description
¬ Objectively defined and internationally agreed upon attributes are
required
¬ ISO JWG14 (TC 130, TC42 & JTC1 SC28 WG4) working on the first
family of image quality attribute standard ISO/TS 18621-x
¬ Join Fogra’s activities and stay up to date
ISO News
Fogra Image Quality Test Suite
http://www.fogra.org/en/fogra-research/wc-digital-printing/digital-printing-currentprojects/imagequality-35003/testforms/test-forms-in-beta.html
Dr. Andreas Kraushaar | [email protected]
http://www.fogra.org/en/fogra-standardization/iso-news-en/a-iso-news-en.html
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PTS Paper and Imaging Symposium, 2014
5. Outlook
From image quality to atmosphere quality
Dr. Andreas Kraushaar | [email protected]
20