8 vertex hans: an ultra-simple printer color architecture
DESCRIPTION
Co-authors: Peter Morovic, Martí Rius and Juan Manuel García-Reyero. Presented at 21st IS&T Color and Imaging Conference on 8th November 2013. "The underlying non-linearity of how print colorants combine makes color control in printing significantly more complex than for other color imaging devices. While in additive systems a measurement of their few primaries and per-channel non-linearities versus luminance is a sufficient basis for predicting color output, printing typically requires the measurement of a large number of colorant combinations. This requirement for many measurements makes accurate color output more challenging and means that setting up a printing system’s color control can be time consuming and costly. The solution presented in this paper involves a new use of the HANS approach, which instead of print optimization looks for simplifying print color formation and therefore also control. In a nutshell this can be achieved by only ever combining eight basic colorant patterns, which results in a display-like color gamut and allows for color control on the basis of their eight measurements and those of the printing system’s optical dot gain."TRANSCRIPT
© Copyright 2013 Hewlett-Packard Development Company, L.P.
Ján Morovič, Peter Morovič, Martí Rius and Juan Manuel García–Reyero Hewlett–Packard Española S. L., Barcelona, Catalonia, Spain
Presented on 8th November 2013 at 21st IS&T Color and Imaging Conference, Albuquerque, NM
eight Vertex hans an ultra &mple printÄ color architecture
© Copyright 2013 Hewlett-Packard Development Company, L.P.
Outline
Background
HANS introduction
A minimal print color architecture
• Associativity of convex combinations • Cube-shaped gamut • The eight-pattern printer
Experimental setup & results
Conclusions
Acknowledgements
© Copyright 2013 Hewlett-Packard Development Company, L.P.
BackgroundHP Designjet Z5400
Color separation LUT 93, 173, 333, 94, 174…
Color calibration LUT N x 9, N x 17, …
Color management
Color calibration
© Copyright 2013 Hewlett-Packard Development Company, L.P.
BackgroundHP Designjet Z5400
Color separation LUT 93, 173, 333, 94, 174…
Color calibration LUT N x 9, N x 17, …
Color management
Color calibration
100s-1000s print +
measure1000s-10Ks
nodes
10s-100s
print + measure +
nodes
© Copyright 2013 Hewlett-Packard Development Company, L.P.
Background
Why do we need so much printing & measurement?
• Print control in colorant space → non-linear channels & their combinations v. colorimetry
• Color separations from RGB/CMYK to colorants non-linear too
• Previous work to optimize choice of samples needed: Monga and Bala, 2008; Morovič et al., 2010; Bianco and Schettini, 2012 …
© Copyright 2013 Hewlett-Packard Development Company, L.P.
Pivot the problem: make system simpler instead of characterizing complexity
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a minimal print /lor architecture
Associativity of convex combinations +
Cube-shaped gamut =
The eight-pattern printer
© Copyright 2013 Hewlett-Packard Development Company, L.P.
Hans basics
Color
Colorant vector
NPac vector
Halftone pattern
Halftone patternH
ANS
Col
oran
tco
ntro
lC=30%, M=40%, Y=0%Interpolate in colorant amounts
W=50%, C=20%, M=10%, Y=0%, CM=20%, CY=0%, MY=0%, CMY=0%interpolate in relative area coverage
Build patterns per colorant& overlay result
Place NPs in singleoperation
C=34%!M=27%!Y=28%!
C=7%!Y=1%!K=27%!
W=77%!C1=1%!Y1=2%!K1=20%!
W=79%!Y1=2%!K1=14%!Y1K1=2%!C2=1%!K2=2%!
W=70%!C1=2%!M1=5%!Y1=5%!K1=6%!C1M1=1%!C1K1=2%!M1K1=3%!Y1K1=2%!C2=4%!
2 basic choices!
6000 basic choices!
© Copyright 2013 Hewlett-Packard Development Company, L.P.
NP basics
A pattern C, formed by combining some of a printing system’s NPs, can be characterized by its NP area coverage (NPac) vector – NPacC
1/3! 2/9! 2/9! 2/9!
k – number of colorant levels / colorant / pixel n – number of colorants, (i.e., the weights are convex) !NPi – the i-the NP T() – color (e.g., Yule-Nielsen-corrected XYZ)
© Copyright 2013 Hewlett-Packard Development Company, L.P.
3sociativity of convex combinationsConvex combination of relative area coverage weighted NP colors can also be seen as the convex combination of two constituent patterns – CA and CB, where wCi = wCBi + wCAi
=! *1/3+! *2/3!
1/3! 2/9! 2/9! 2/9! 1/3! 2/3! 1/3! 1/3! 1/3!
1/9! 2/9! 2/9! 2/9!2/9!
*1/3! *2/3!
© Copyright 2013 Hewlett-Packard Development Company, L.P.
consequencÑ of associativity
Consequence of associativity: convex combinations not only of at-pixel states (i.e., Neugebauer Primaries), but also of a pattern’s sub-patterns.
• New NPacs can be constructed by convexly combining other NPacs, and this process can, in principle, go on ad infinitum.
0!
10!
20!
30!
40!
50!
0! 20! 40! 60! 80!
light
ness!
chroma!
ink!
area coverage!
Yn
0!
25!
50!
area
cov
erag
e (%
)! C!
W!
CM!
K!
M!
Xn
© Copyright 2013 Hewlett-Packard Development Company, L.P.
herzog 1be shaped gamut
© Copyright 2013 Hewlett-Packard Development Company, L.P.
BLACK
YELLOW
GREENBLUE
CYAN
RED
MAGENTA
WHITE
BLACKRED
MAGENTA
WHITECYAN
GREEN
BLUE
YELLOW
Device RGB Interface
Yule-Nielsen XYZ measurments of HANS NPac characterisation chart
Print & measure NPs and NPacs
Select 8 vertices in correspondence with RGB cube
Apply tetrahedral RGB tessellation to 8 vertices in XYZn
Do tetrahedra
in XYZn overlap?
RGB-NPac-XYZ LUT
YES
NO
the eight
Êttern
printer
© Copyright 2013 Hewlett-Packard Development Company, L.P.
8-vertex HANS pipeline • 23 LUT with 8 NPacs at RGB cube’s
vertices, tessellated by 6 tetrahedra, sharing B-W long diagonal of RGB cube
HP Designjet Z6200 printer • CMYK pigmented inks • 90 g/m2 HP Coated Paper
substrate
83=512 color test chart measured using printer’s embedded 45°/0° spectrophotometer under D50
Color differences • CIE ∆E2000s between chart’s
measurements and predictions from eight RGB vertex measurements + estimate of printer’s Yule-Nielsen-modeled dot gain
experimentA setup
© Copyright 2013 Hewlett-Packard Development Company, L.P.
© Copyright 2013 Hewlett-Packard Development Company, L.P.
every color is convex
combination of up to 4 basic
patterns
gamut is convex
© Copyright 2013 Hewlett-Packard Development Company, L.P.
resU lts
mean = 1.59 95th percentile = 3.96 maximum = 5.54
Once non-linearity is characterized, color control by measuring only eight basic colorant halftone patterns • Good enough for ICC profiling • Same measurements can be used for calibration • Largest inscribed convex octahedral gamut
0 2 4 6 80
∆E2000
20
40
60
80
100
120
frequency
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the eight Pattern solution
Color separation LUT: 23
Color calibration LUT: N x 2
Color management
© Copyright 2013 Hewlett-Packard Development Company, L.P.
the eight Pattern solution
Color separation LUT: 23
Color calibration LUT: N x 2
Color management
EIGHT × print +
measure + node
© Copyright 2013 Hewlett-Packard Development Company, L.P.
con(usionsHANS NPac control enables ultra-simple print color formation and control
• Minimal color setup requirements → calibration & profiling from 8 measurements
• Convex, ‘flat-faced’ gamut → gamut mapping
• 8-node look-up table → throughput / efficiency / cost
© Copyright 2013 Hewlett-Packard Development Company, L.P.
acknoWledgements
Will Allen
Carlos Amselem
David Gaston
Rafa Gimenez
Jordi Sender“To be honest, I would never have invented the
wheel, if not for Urg’s ground-breaking theoretical work with the circle.”!
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thanK You