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Claims  |
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What is claimed is:
1. A method of correcting data in an input device dependent digital color
image generated at an input device, preparatory to reproduction at a
plural channel output device, comprising the steps of:
a) providing input device dependent color image signals in an input device
dependent color space said device dependent color image signals having
been sub-sampled;
b) providing information about the color response characteristic of the
input device and the output device;
c) using said information, mapping said input device dependent color image
signals to output device dependent color image signals at said plurality
of channels in an output device dependent color space, said output device
dependent color space being an RGB space, with a complex mapping process
which includes color correction, wherein said output device dependent
color image signals correspond to said input device dependent color image
signals said processing comprising:
i) deriving a set of input device dependent master signals from said input
device dependent color image signals by designating a signal set at a
given location within each block wherein said input device dependent color
imaging signals are received at three channels, wherein a first channel L
receives luminance signals at a luminance channel resolution, a second
channel Cr receives red-green chrominance signals at a red-green
chrominance channel resolution, and a third channel Cb receives
blue-yellow chrominance signals at a blue-yellow chrominance resolution;
ii) mapping said input device dependent master signal set to an output
device dependent master signal set in said output device dependent color
space, said mapping comprising: dividing the digital color image into
blocks, each block including a plurality of device dependent signal sets,
wherein each signal set includes a signal from each of said channels, and
wherein each block includes one master signal set; and applying a look up
table conversion to transform said master signal set from said device
dependent color space to said output device dependent color space; and
iii) defining output device dependent color image signals corresponding to
a subset of said input device dependent color signals, said defining step
further comprises creating output device dependent signals for each signal
set in said block according to a luminance signal for each signal set
relative to a luminance of said master signal set; and wherein said
creating step comprising: setting output device dependent signal
Rij=(Rm/Lm)Lij; setting output device dependent signal Gij=(Gm/Lm)Lij; and
setting output device dependent signal Bij=(Bm/Lm)Lij for each signal set
Pij in said block, wherein ii denotes a location of each set within said
block, Lij is said luminance signal of signal set Pij, Rm, Gm, and Bm are
master signal set output device dependent signals and Lm is said master
signal set luminance signal; and
d) converting said output device dependent color image signals with a
simple color conversion method to output device dependent coordinate
signals which correspond to output device colorants.
2. A method of correcting data as claimed in claim 1 wherein said master
signal set deriving step further comprises designating a pseudo-signal
that has L channel, Cr channel, and Cb channel signals equal to the mean L
channel, Cr channel, and Cb channel signals for all signal sets in said
block.
3. A method of correcting data as claimed in claim 1 wherein said master
signal set deriving step further comprises choosing a desired relative
luminance signal.
4. A method of correcting data as claimed in claim 3 wherein said chosen
luminance signal is a maximum signal of all luminance signals in said
block.
5. A method of correcting data as claimed in claim 3 wherein said chosen
luminance signal is nearest to an average for all luminance signals in
said block.
6. A method of correcting data as claimed in claim 1 wherein said creating
step further comprises:
a) setting output device dependent signal Rij=a (loga Rm-loga Lm+loga Lij);
b) setting output device dependent signal Gij=a (loga Gm-loga Lm+loga Lij);
and
c) setting output device dependent signal Bij=a (loga Bm-loga Lm+loga Lij)
for each signal set Pij in said block, wherein ij denotes a location of
each signal set within said block, Lij is said luminance signal of signal
set Pij , Rm, Gm, and Bm are master signal set output device dependent
signals and Lm is said master signal set luminance signal.
7. A method of correcting data as claimed in claim 1 wherein said creating
step further comprises:
a) setting output device dependent signal Rij=Rm-Lm+Lij
b) setting output device dependent signal Gij=Gm-Lm+Lij; and
c) setting output device dependent signal Bij=Bm-Lm+Lij
for each signal set Pij in said block, wherein ij denotes a location of
each signal set within said block, Lij is said luminance signal of signal
set Pij, Rm, Gm, and Bm are master signal set output device dependent
signals and Lm is said master signal set luminance signal.
8. A method of correcting data as claimed in claim 1 wherein said output
device dependent color space is an LCrCb space.
9. A method of correcting data as claimed in claim 8 wherein said creating
step further comprises:
a) setting output device dependent signal L.sub.ij '=(L.sub.m
'/L.sub.m)L.sub.ij ;
b) setting output device dependent signal Cr.sub.ij '=(L.sub.m
'/L.sub.m)Cr.sub.ij ;
c) setting output device dependent signal Cb.sub.ij '=(L.sub.m
'/L.sub.m)Cb.sub.ij ; for each signal set P.sub.ij in said block, wherein
ij denotes a location of each set within said block, L.sub.ij is said
device dependent luminance signal of signal set P.sub.ij, L.sub.m ', is
said master signal set output device dependent signal, and L.sub.m is said
master signal set device dependent luminance signal.
10. A method of correcting data as claimed in claim 1 wherein an output
device dependent color space is a CMYK color space.
11. A method of correcting data as claimed in claim 10 wherein said
defining step further comprises:
a) setting output device dependent coordinate signal C.sub.ij
=1-((1-C.sub.m)/L.sub.m) L.sub.ij ;
b) setting output device dependent coordinate signal M.sub.ij
=1-((1-M.sub.m)/L.sub.m)L.sub.ij ;
c) setting output device dependent coordinate signal Y.sub.ij
=1-((1-Y.sub.m)/L.sub.m)L.sub.ij ; and
d) setting output device dependent coordinate signal K.sub.ij =K.sub.m,
for each signal set P.sub.ij in said block, wherein ij denotes a location
of each signal set within said block, L.sub.ij is said luminance signal of
signal set P.sub.ij, C.sub.m, M.sub.m, Y.sub.m, and K.sub.m are master
signal set device dependent color image signals and L.sub.m is a master
signal set luminance signal.
12. A method of correcting data as claimed in claim 1 wherein said
red-green channel resolution is less than said luminance channel
resolution and said blue-yellow channel resolution is less than said
red-green channel resolution.
13. A method of correcting data as claimed in claim 12 wherein said master
signal deriving step further comprises:
a) dividing the digital color image into a plurality of blocks, and further
dividing said blocks into a plurality of sub-blocks, wherein each block
includes a plurality of signal sets that have a substantially constant
blue-yellow resolution, and each sub-block includes a plurality of signal
sets that have substantially constant red-green chrominance and
blue-yellow resolutions;
b) selecting a master sub-block; and
c) choosing a signal set within said master sub-block as said master signal
set.
14. A method of correcting data as claimed in claim 13 wherein said mapping
step further comprises:
a) applying a look up table conversion to transform said master signal set
from said device dependent color space to said output device dependent
color space;
b) correcting said output device dependent red-green chrominance signals
for a subset of said sub-blocks; and
c) correcting said output device dependent luminance signals for a subset
of said signal sets.
15. A method of correcting data as claimed in claim 14 wherein said master
sub-block selecting step further comprises designating a sub-block at a
given location within each block.
16. A method of correcting data as claimed in claim 14 wherein said master
sub-block selecting step further comprises creating a pseudo-sub-block
that has L channel and Cr channel signals equal to the mean L channel and
Cr channel signals for all signal sets in said block.
17. A method of correcting data as claimed in claim 14 wherein said master
sub-block selecting step further comprises designating a desired relative
red-green chrominance signal.
18. A method of correcting data as claimed in claim 17 wherein said
designated red-green chrominance signal is a maximum magnitude of all
chrominance red-green chrominance signals in said block.
19. A method of correcting data as claimed in claim 17 wherein said
designated red-green chrominance signal is nearest to an average for all
red-green chrominance signals in said block.
20. A method of correcting data as claimed in claim 14 wherein said master
signal set choosing step further comprises designating a signal set at a
given location within each sub-block.
21. A method of correcting data as claimed in claim 14 wherein said master
signal set choosing step further comprises designating a desired relative
luminance signal.
22. A method of correcting data as claimed in claim 21 wherein said
designated luminance signal is a maximum signal of all luminance signals
in said sub-block.
23. A method of correcting data as claimed in claim 21 wherein said
designated luminance signal is nearest to an average for all luminance
signals in said sub-block.
24. A method of correcting data as claimed in claim 14 wherein said output
device dependent color space is an RGB space.
25. A method of correcting data as claimed in claim 24 wherein said
red-green chrominance correcting step further comprises:
a) setting L.sub.ij '=L.sub.m '(L.sub.ij /L.sub.m);
b) setting R.sub.ij '=(R.sub.m /L.sub.m)L.sub.ij ;
c) setting G.sub.ij '=(G.sub.m /L.sub.m)L.sub.ij ;
d) setting R.sub.ij "=R.sub.ij'(Cr.sub.kl +Cr)/2Cr.sub.kl +G.sub.ij
'(Cr.sub.kl -Cr)/2Cr.sub.kl ;
e) setting G.sub.ij "=R.sub.ij '(Cr.sub.kl -Cr)/2Cr.sub.kl +G.sub.ij
'(Cr.sub.kl +Cr)/2Cr.sub.kl, and
f) setting B.sub.ij "=B.sub.ij'
where Cr.sub.ij '=R.sub.ij '-G.sub.ij ', and B.sub.ij '=Cb.sub.ij
'+(R.sub.ij +G.sub.ij ')/2.
26. A method of correcting data as claimed in claim 24 wherein said
red-green chrominance correcting step further comprises:
a) setting R.sub.ij "=a**(Ir+Iplus-Idenom)+a**(Ig+Iminus-Idenom); and
b) setting G.sub.ij "=a**(Ir-Iplus+Idenom)+a**(Ig-Iminus+Idenom) where
Iplus=log.sub.a [Cr.sub.kl +Cr], Iminus=log.sub.a [Cr.sub.kl -Cr], and
Idenom=log.sub.a [2Cr.sub.kl ].
27. A method of correcting data as claimed in claim 14 wherein said output
device dependent color space is an LCrCb space.
28. A method of correcting data as claimed in claim 27 wherein said
red-green chrominance correcting step further comprises setting
Crkl'=Crm'(Crkl/Crm) for each sub-block, and said luminance correcting
step further comprises setting Lij'=Lm'(Lij/Lm) for each signal set,
wherein kl denotes a location of each sub-block within said block, Crkl'
is an output device dependent red-green chrominance signal of sub-block
Skl, Crm' is an output device dependent red-green chrominance master
signal, Crkl is a device dependent red-green chrominance signal of
sub-block Ski, and Crm is a device dependent red-green chrominance master
signal, and wherein ij denotes a location of each signal set within said
block, Lij' is an output device dependent luminance signal of signal set
Pij, Lm' is an output device dependent master signal set luminance signal,
Lij is a device dependent luminance signal of signal set Pij, Lm is a
device dependent master signal set luminance signal.
29. A method of correcting data as claimed in claim 14 wherein an output
device dependent color space is a CMYK color space.
30. A method of correcting data as claimed in claim 29 wherein said
defining step further comprises:
a) setting output device dependent coordinate signal C.sub.ij
=1-((1-C.sub.m)/L.sub.m)L.sub.ij ;
b) setting output device dependent coordinate signal M.sub.ij
=1-((1-M.sub.m)/L.sub.m)L.sub.ij ;
c) setting output device dependent coordinate signal Y.sub.ij
=1-((1-Y.sub.m)/L.sub.m)L.sub.ij ; and
d) setting output device dependent coordinate signal K.sub.ij =K.sub.m,
for each signal set P.sub.ij in said block, wherein ij denotes a location
of each signal set within said block, L.sub.ij is said luminance signal of
signalset P.sub.ij, C.sub.m, M.sub.m, Y.sub.m, and K.sub.m are master
signal set device dependent color image signals and Lm is a master signal
set luminance signal.
31. An apparatus for correcting data in a device dependent digital color
image generated at an input device, preparatory to reproduction at a
plural channel output device, comprising:
a) means for providing input device dependent color image signals in an
input device dependent color space said device dependent color image
signals having been sub-sampled;
b) means for mapping said input device dependent color image signals to
output device dependent color image signals at a plurality of channels in
an output device dependent color space, said output device dependent color
space being an RGB space, with a complex color mapping process which
includes color correction said processing means further comprises:
i) means for deriving a set of input device dependent master signals from
said input device dependent color image signals by designating a signal
set at a given location within each block wherein said input device
dependent color imaging signals are received at three channels, wherein a
first channel L receives luminance signals at a luminance channel
resolution, a second channel Cr receives red-green chrominance signals at
a red-green chrominance channel resolution, and a third channel Cb
receives blue-yellow chrominance signals at a blue-yellow chrominance
resolution;
ii) means for mapping said input device dependent master signal set to an
output device dependent master signal set in said output device dependent
color space, said means for mapping comprising:
means dividing the digital color image into blocks, each block including a
plurality of device dependent signal sets, wherein each signal set
includes a signal from each of said channels, and wherein each block
includes one master signal set; and
means for applying a look up table conversion to transform said master
signal set from said device dependent color space to said output device
dependent color space; and
iii) means for defining output device dependent color image signals
corresponding to a subset of said input device dependent color signals,
said means for defining comprising means for creating output device
dependent signals for each signal set in said block according to a
luminance signal for each signal set relative to a luminance of said
master signal set; and wherein said means for creating comprises: means
for setting output device dependent signal Rij=(Rm/Lm)Lij; means for
setting output device dependent signal Gij=(Gm/Lm)Lij; and means for
setting output device dependent signal Bij=(Bm/Lm)Lij for each signal set
Pij in said block, wherein ij denotes a location of each set within said
block, Lij is said luminance signal of signal set Pij, Rm, Gm, and Bm are
master signal set output device dependent signals and Lm is said master
signal set luminance signal; and
c) means for providing information about the color response characteristic
of the input device and the output device, and
d) means, using said information provided, for converting said output
device dependent color image signals to output device dependent coordinate
signals which correspond to output device colorants with a simple color
space conversion method.
32. An apparatus for correcting data as claimed in claim 31 wherein said
creating means further comprises:
a) means for setting output device dependent signal R.sub.ij =a (log.sub.a
Rm-log.sub.a L.sub.m +log.sub.a L.sub.ij);
b) means for setting output device dependent signal G.sub.ij =a (log.sub.a
G.sub.m -log.sub.a L.sub.m +log.sub.a L.sub.ij); and
c) means for setting output device dependent signal B.sub.ij =a (log.sub.a
B.sub.m -log.sub.a L.sub.m +log.sub.a L.sub.ij)
for each signal set P.sub.ij in said block, wherein ij denotes a location
of each signal set within said block, L.sub.ij is said luminance signal of
signal set P.sub.ij, R.sub.m, G.sub.m, and B.sub.m are master signal set
output device dependent signals and L.sub.m is said master signal set
luminance signal.
33. An apparatus for correcting data as claimed in claim 31 wherein said
creating means further comprises:
a) means for setting output device dependent signal R.sub.ij =R.sub.m
-L.sub.m +L.sub.ij
b) means for setting output device dependent signal G.sub.ij =G.sub.m
-L.sub.m +L.sub.ij ; and
c) means for setting output device dependent signal B.sub.ij =B.sub.m
-L.sub.m +L.sub.ij
for each signal set P.sub.ij in said block, wherein ij denotes a location
of each signal set within said block, L.sub.ij is said luminance signal of
signal set P.sub.ij, R.sub.m, G.sub.m, and B.sub.m are master signal set
output device dependent signals and L.sub.m is said master signal set
luminance signal.
34. An apparatus for correcting data as claimed in claim 31 wherein said
creating means further comprises:
a) means for setting output device dependent signal L.sub.ij '=(L.sub.m
'/L.sub.m)L.sub.ij ;
b) means for setting output device dependent signal Cr.sub.ij '=(L.sub.m
'/L.sub.m)Cr.sub.ij ;
c) means for setting output device dependent signal Cb.sub.ij '=(L.sub.m
'/L.sub.m)Cb.sub.ij ;
for each signal set P.sub.ij in said block, wherein ij denotes a location
of each set within said block, L.sub.ij is said device independent
luminance signal of signal set P.sub.ij, L.sub.m ', is said master signal
set output device dependent signal, and L.sub.m is said master signal set
device independent luminance signal.
35. An apparatus for correcting data as claimed in claim 31 wherein said
defining means further comprises:
a) means for setting output device dependent coordinate signal C.sub.ij
=1-((1-C.sub.m)/L.sub.m)L.sub.ij ;
b) means for setting output device dependent coordinate signal M.sub.ij
=1-((1-M.sub.m)/L.sub.m)L.sub.ij ;
c) means for setting output device dependent coordinate signal Y.sub.ij
=1-((1-Y.sub.m)/L.sub.m)L.sub.ij ; and
d) means for setting output device dependent coordinate signal K.sub.ij
=K.sub.m,
for each signal set P.sub.ij in said block, wherein ij denotes a location
of each signal set within said block, L.sub.ij is said luminance signal of
signal set P.sub.ij, C.sub.m, M.sub.m, Y.sub.m, and K.sub.m are master
signal set device dependent color image signals and L.sub.m is a master
signal set luminance signal.
36. An apparatus for correcting data as claimed in claim 31 wherein said
master signal deriving means further comprises:
a) means for dividing the digital color image into a plurality of blocks,
and further dividing said blocks into a plurality of sub-blocks, wherein
each block includes a plurality of signal sets that have a substantially
constant blue-yellow resolution, and each sub-block includes a plurality
of signal sets that have substantially constant red-green chrominance and
blue-yellow resolutions;
b) means for selecting a master sub-block; and
c) means for choosing a signal set within said master sub-block as said
master signal set.
37. An apparatus for correcting data as claimed in claim 36 wherein said
mapping means further comprises:
a) means for applying a look up table conversion to transform said master
signal set from said device independent color space to said output device
dependent color space;
b) correcting said output device dependent red-green chrominance signals
for a subset of said sub-blocks; and
c) correcting said output device dependent luminance signals for a subset
of said signal sets.
38. An apparatus for correcting data as claimed in claim 37 wherein said
red-green chrominance correcting means further comprises:
a) means for setting L.sub.ij '=L.sub.m '(L.sub.ij /L.sub.m);
b) means for setting R.sub.ij '=(R.sub.m /L.sub.m)L.sub.ij ;
c) means for setting G.sub.ij '=(G.sub.m /L.sub.m)L.sub.ij ;
d) means for setting R.sub.ij "=R.sub.ij '(Cr.sub.kl +Cr)/2Cr.sub.kl
+G.sub.ij '(Cr.sub.kl -Cr)/2Cr.sub.kl ;
e) means for setting G.sub.ij "=R.sub.ij '(Cr.sub.kl -Cr)/2Cr.sub.kl
+G.sub.ij '(Cr.sub.kl +Cr)/2Cr.sub.kl, and
f) means for setting B.sub.ij "=B.sub.ij '
where Cr.sub.ij '=R.sub.ij '-G.sub.ij ', and B.sub.ij '=Cb.sub.ij
'+(R.sub.ij '+G.sub.ij ')/2.
39. An apparatus for correcting data as claimed in claim 37 wherein said
red-green chrominance correcting means further comprises:
a) means for setting R.sub.ij "=a**(Ir+Iplus-Idenom)+a**(Ig+Iminus-Idenom);
and
b) means for setting G.sub.ij "=a**(Ir-Iplus+Idenom)+a**(Ig-Iminus+Idenom)
where Iplus=log.sub.a [Cr.sub.kl +Cr], Iminus=log.sub.a [Cr.sub.kl -Cr],
and Idenom=log.sub.a [2Cr.sub.kl ].
40. An apparatus for correcting data as claimed in claim 37 wherein said
red-green chrominance correcting means further comprises means for setting
Cr.sub.kl '=Cr.sub.m '(Cr.sub.kl /Cr.sub.m) for each sub-block, and said
luminance correcting means further comprises means for setting L.sub.ij
'=L.sub.m '(L.sub.ij /L.sub.m) for each signal set, wherein kl denotes a
location of each sub-block within said block, Cr.sub.kl ' is an output
device dependent red-green chrominance signal of sub-block Ski, Cr.sub.m '
is an output device dependent red-green chrominance master signal,
Cr.sub.kl is a device independent red-green chrominance signal of
sub-block S.sub.kl, and Cr.sub.m is a device independent red-green
chrominance master signal, and wherein ij denotes a location of each
signal set within said block, L.sub.ij ' is an output device dependent
luminance signal of signal set P.sub.ij, L.sub.m ' is an output device
dependent master signal set luminance signal, L.sub.ij is a device
independent luminance signal of signal set P.sub.ij, L.sub.m is a device
independent master signal set luminance signal.
41. An apparatus for correcting data as claimed in claim 37 wherein said
defining means further comprises:
a) means for setting output device dependent coordinate signal C.sub.ij
=1-((1-C.sub.m)/L.sub.m)L.sub.ij ;
b) means for setting output device dependent coordinate signal M.sub.ij
=1-((1-M.sub.m)/L.sub.m)L.sub.ij ;
c) means for setting output device dependent coordinate signal Y.sub.ij
=1-((1-Y.sub.m)/L.sub.m)L.sub.ij ; and
d) means for setting output device dependent coordinate signal K.sub.ij
=K.sub.m,
for each signal set P.sub.ij in said block, wherein ij denotes a location
of each signal set within said block, L.sub.ij is said luminance signal of
signal set P.sub.ij, C.sub.m, M.sub.m, Y.sub.m, and K.sub.m are master
signal set device dependent color image signals and L.sub.m is a master
signal set luminance signal. |
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Claims |
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Description |
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The present invention is directed to a method of improving the efficiency
of color correcting full resolution, averaged or subsampled luminance and
chrominance based data. More specifically, the present invention is
directed to a method of reducing the amount of data that is required to
accurately describe a digital color image, and the processing resources
required to color correct that data.
BACKGROUND OF THE INVENTION
Data reduction is required in data handling processes, where too much data
is present for practical applications using the data. Generally speaking,
digital images--images that have been discretized in both spatial
coordinates and in brightness levels such as those acquired by
scanning--are often large, and thus make desirable candidates for at least
one form of data reduction. These digital images do not typically change
very much on a pixel to pixel basis and have what is known as "natural
spatial correlation." For example in a digital color image, it is commonly
known that the required spatial resolution for chrominance data is less
than the spatial resolution for luminance data. The natural spatial
correlation enables reducing not only the digital image data, but the
resources required by certain image processing operations on the reduced
data.
Digital color images may be described in terms of the chrominance and
luminance values for each pixel contained therein. It is obviously desired
to reproduce color images such that the colors in the copy exactly, or at
least closely match the corresponding colors in the original image. Since
image input and output devices are often quite different, reproducing an
accurate color image often requires some form of color correction to be
applied to the chrominance and luminance data before it is output. Color
correction in digital images for a printing device is an image processing
operation which may include a correction from 3-D device independent color
space (e.g., YC.sub.r C.sub.b, RGB, XYZ, or L*a*b) to a 3-D device
dependent color space; and then a conversion to CMYK comprising
under-color removal (UCR), gray-component replacement (GCR) and
linearization processes.
The time required for color conversions such as those described above is
directly proportional to the amount of data to which it is applied. Thus,
it is desirable in many applications to employ some form of data reduction
in order to facilitate rapid image processing. In addition to compression,
subsampling schemes are used in scanners, digital copiers or other devices
that are used to reproduce, store or process color documents. Briefly, a
subsampling scheme involves selecting some subset of the available
original image data for subsequent image processing operations. This
substantially reduces the volume of data that is subsequently generated
and converted, preferably with little or no impact on the appearance of
the reproduced image. Any combination of luminance and chrominance data
where at least one of the chrominance channels is at a reduced density is
generally referred to as subsampled luminance and chrominance data.
There are various luminance-chrominance color spaces, including the CIE
standard L*a*b*, and L*u*v*; and industry standard YCrCb. One could also
define a simply computed luminance-chrominance space for a specific
purpose. The distinguishing feature of a luminance-chrominance space is
that one of the three axes represents the luminance, or lightness of the
color, while the other two together represent the hue (related to the
color name) and colorfulness or purity. For simplicity, we use LCrCb to
mean any luminance chrominance space with L as the luminance channel and
Cr and Cb as the other two channels, which represent the difference R-G of
the amount of red and green, and the difference B-Y of the amount of blue
and yellow respectively that is present in the image at a given pixel.
The present invention may be used to reduce the resources required to
reproduce a digital color image. The invention may be used when full
resolution luminance and chrominance data is available, or when the data
has been previously reduced using subsampling, compression or other known
techniques. Rather than performing color correction on all of the pixels
in an image, the method disclosed selects one pixel in each block for full
conversion from the LC.sub.r C.sub.b color space to the CMYK color space.
Device values are then assigned to the remaining pixels by combining the
converted device data for the selected pixel with the luminance data for
the remaining pixels.
The following disclosures may be relevant to aspects of the present
invention:
U.S. Pat. No. 4,275,413 to Sakamoto et al. issued Jun. 23, 1981 discloses a
color space transformation where information is placed into lookup tables
and stored in a memory--where the lookup table relates input color space
to output color space. Sakamoto teaches a "unit cube interpolation unit"
having known vertices. The lookup table is commonly a three dimensional
table since color is typically defined with three variables.
U.S. Pat. No. 5,581,376 to Harrington issued Dec. 3, 1996 teaches the
conversion of input device signals Rs, Gs, Bs, generated by an image input
terminal, to calorimetric values Rc, Gc, Bc, the colorimetric values being
processed to generate address entries into a lookup table to convert them
to Cx, Mx, Yx, Kx colorant signals or any multi-dimensional output color
space, which includes but is not limited to CMYK or spectral data. Values
not directly mapped may be determined using tetrahedral interpolation over
a hexagonal lattice where the lattice is formed by offsetting every other
row in at least one dimension.
U.S. Pat. No. 5,477,345 to Tse issued Dec. 19, 1995 relates to subsampling
processors and a three color sensor array that may be employed to supply
subsampled chrominance data to a printing machine, a computer memory
device or other device.
U.S. Pat. No. 5,067,010 to Ishii et al. issued Nov. 19, 1991 discloses a
color video signal processing device in which pixels are thinned out for a
whole picture plane with respect to each of two kinds of digital color
difference signals in accordance with a predetermined role. The encoding
is executed on a unit basis of a block consisting of (n.times.m) samples
where (n and m are integers no less than 2) which are formed with respect
to each of the two kinds of color difference signals whose pixels have
been thinned out or a block consisting of (n.times.m) samples formed so as
to include both of the two kinds of color difference signals whose pixels
had been thinned out. The data compression is executed on a block unit
basis.
U.S. Pat. No. 4,656,515 to Christopher issued Apr. 7, 1987 discloses a
television display including circuitry for reducing the amount of memory
needed to hold one field of the reduced size image. In the display
apparatus, digital samples repres | | |
