Computer graphics processing and selective visual display system – Computer graphics processing – Attributes
Reexamination Certificate
1999-10-29
2002-06-25
Brier, Jeffery (Department: 2672)
Computer graphics processing and selective visual display system
Computer graphics processing
Attributes
C345S589000, C345S591000, C345S604000
Reexamination Certificate
active
06411304
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a color data conversion apparatus for converting first color data included in a first color gamut of color image equipment such as a CRT, according to prespecified target color data within a second color gamut of another color image equipment such as a printer, to second color data within the second color gamut as well as to a color data conversion method and a recording medium for the same. More particularly, this invention relates to a color data conversion apparatus enabling efficient performance of color data conversion without increase in its lightness when an image fetched through a scanner is displayed on a CRT or a result of an image printed by a printer is reproduced on a CRT as well as to a color data conversion method and a recording medium for the same.
BACKGROUND OF THE INVENTION
Conventionally, color image equipment such as a printer and a CRT has, in many cases, a different color gamut. Therefore, there may arise a case where a color capable of being displayed on a CRT can not be printed. Disclosed in Japanese Patent Laid-Open Publication No. SHO 60-105376 (Conventional technology
1
) is a color image output device for converting color data included in the first color gamut dependent on first color input/output equipment toward an achromatic color having the same lightness as that of the first color data tobe converted to second color data included in the second color gamut dependent on second color input/output equipment.
FIGS. 13A and 13B
explain the concepts of conventional color data conversion for converting color data included in a color gamut of a CRT to color data included in a color gamut of a printer on a L*a*b* space. An area
301
indicated by a broken line in these figures shows a color gamut of a CRT, and an area
302
indicated by a solid line shows a color gamut of a printer In this L*a*b* space, lightness becomes higher as an L* value is larger, chroma becomes higher as values of a* and b* become larger. Positive area of b* is mainly a yellow gamut, while negative area of b* is mainly a blue gamut.
As shown in
FIG. 13A
, color data
303
,
306
,
309
, and
312
displayable on a CRT are outside of the printer color gamut, therefore the color data
303
,
306
,
309
, and
312
cannot be printed by a printer unless they are converted to data for a printer.
Therefore, in accordance with the conventional technology
1
, when a color of the color data
303
is to be converted to a color within the printer color gamut
302
, by marking color data
304
for an achromatic color having the same lightness as that of the color data
303
and converting the color of the color data
303
toward the color data
304
, color data
305
corresponding to the color data
303
is acquired.
Also, when a color of the color data
306
for blue with high chroma is to be converted to a color within the printer color gamut
302
, by marking color data
307
for an achromatic color having the same lightness as that of the color data
306
and converting the color of the color data
306
toward the color data
307
, color data
308
corresponding to the color data
306
is acquired. Similarly, the color data
309
is converted toward color data
310
to acquire color data
311
, and the color data
312
is converted toward color data
313
to acquire color data
314
.
As described above, in the conventional technology
1
, when the color data
303
,
306
,
309
, and
312
are to be printed, the color data
305
,
308
,
311
, and
314
are used in place of the color data described above.
However, the conventional technology
1
has a problem (described as “problem
1
” hereinafter) that when the color data
303
for yellow with high chroma and the color data
306
for blue with high chroma are converted, the chroma tends to degrade more. For example, when an image of a banana or a lemon photographed by a digital camera or an image of bright-colored printed matter inputted with a color scanner is printed, chroma of yellow is largely lost, thus the image becomes unnatural.
There is another problem (described as “problem
2
” hereinafter) that even if the color data
315
and
317
shown in
FIG. 13A
are converted by using the conventional technology
1
, the converted color data may be color data
316
and
318
which are outside of the printer color gamut
302
.
Therefore, disclosed in a paper “Colour Reproduction Theory based on the Principles of Colour Science” written by Laihanen, P. (Conventional technology
2
) is a technology in which all of the first color data included in the first color gamut dependent on the first color input/output equipment is converted toward an achromatic color having an intermediate lightness value between the highest lightness value and the lowest lightness value of the second color gamut to be converted to the second color data included in the second color gamut dependent on the second color input/output equipment.
FIG. 13B
explains the concepts of color data conversion based on the conventional technology
2
. As shown in this figure, in the conventional technology
2
, color data
326
and
328
which are outside of the printer color gamut
302
are converted toward color data
322
for an achromatic color having an intermediate lightness value between the highest lightness value and the lowest lightness value of the printer color gamut
302
, and color data
327
and
329
are respectively acquired.
Namely, in the conventional technology
2
, the color data
322
is insured to always exist within the printer color gamut
302
. Therefore any color can be printed by a printer, which is different from the conventional technology
1
. Thus the problem
2
is solved. In addition, with the conventional technology
2
, high-chroma yellow color data
321
is converted to color data
323
, and high-chroma blue color data
324
is converted to color data
325
, therefore decrease in chroma is reduced as compared to that of the conventional technology
1
. Thus the problem
1
is solved.
When the conventional technology
2
is used, however, there comes up an extremely significant problem (described as “problem
3
” hereinafter) that each relation of both lightness values and chroma values between two color data is concurrently reversed respectively, which is called, reversion of gray scale. Especially, the reversion of gray scale described above becomes sever when a relation between a lightness value A of color data before conversion, a lightness value B of the color data
332
which is at the same hue angle as that of the color data and also has the highest chroma included in the printer color gamut
302
, and a lightness value C of the color data
322
for an achromatic color having the intermediate lightness value is A>B>C or A<B<C.
For example, referring to the color data
330
and the color data
321
shown in
FIG. 13B
, original lightness and chroma values of the color data
321
are higher than the lightness value and chroma value of the color data
330
. However, if the color data
331
to which the color data
330
is converted and the color data
323
to which the color data
321
is converted are compared, then it can be understood that the lightness value and chroma value of the color data
331
are higher than the lightness value and chroma value of the color data
323
. Thus, a reversion of gray scale has occurred.
In the Japanese Patent Laid-Open Publication No. HEI 10-8865 applied on Jan. 20, 1998 by the applicant of the present application (conventional technology
3
) a color data conversion method has been disclosed for converting first color data included in the first color gamut dependent on the first color input/output equipment toward third color data locating on a line linking color data which is at the same hue angle as that of the first color data and also has the highest chroma of the colors included in the second color gamut dependent on the second color input/output equipment to color data for an achromatic color which is at the same hue angle
Semba Satoshi
Shimizu Masayoshi
Suzuki Shoji
Blackman Anthony J.
Brier Jeffery
Fujitsu Limited
Staas & Halsey , LLP
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