Color image forming method and an apparatus employed therefor, and a correction factor determining method

• US 5,422,738 A
• Filed: 04/18/1994
• Issued: 06/06/1995
• Est. Priority Date: 10/22/1990
• Status: Expired due to Term

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Ishihara, Hideshi, Yamashita, Haruo, Matsumoto, Yasuki
• Primary Examiner(s): Coles, Sr., Edward L.
• Assistant Examiner(s): NING, JOHN K
• Application Number:
  US08/229,053
• Time in Patent Office: 414 Days
• Field of Search: 358/500, 358/517, 358/518, 358/515, 358/523
• US Class Current: 358/500
• CPC Class Codes: H04N 1/6019 using look-up tables H04N1/6025 takes precedence

Abstract

A color image forming method and an apparatus to be used for executing the method are provided which are capable of effecting more faithful color reproduction with respect to a target color, and also, a color correction factor determining method to be used in the above method and apparatus. The color image forming apparatus to which the color image forming method is applied is arranged to subject three primary color luminance signals (R, G, B) to linear matrix calculation by a luminance matrix device for conversion into second luminance signals (R'"'"', G'"'"', B'"'"') to correct deviation of wavelength of the spectral absorbing characteristic of the ink, and to subject each color of the second luminance signals (R'"'"', G'"'"', B'"'"') to complementary color conversion into three primary color density signals (D_R, D_G, D_B) by a complementary color converting device, and further, to subject the three primary color density signals (D_R, D_G, D_B) to color correcting calculation by a color correcting device for conversion into ink density signals (C, M, Y), so as to correct color turbidity due to the unnecessary component of the ink. Additionally, the correction factor determining method determines the luminance matrix factor used for the luminance matrix calculation and the color correction factor used for the color correcting calculation by minimizing conditions of a color difference to be perceived by man.

Claims

1. A method of forming a color image which comprises the steps of:

a) subjecting three primary color luminance signals (R,G,B) of additive color mixture to matrix conversion into second luminance signals (R'"'"', G'"'"', B'"'"')

b) subjecting each color of said second luminance signals (R'"'"', G'"'"', B'"'"') to complementary color conversion into three primary color density signals (D_R, D_G, D_B) of subtractive color mixture,

c) subjecting each color of said three primary color density signals (D_R, D_G, D_B) to non-linear conversion into signals (C'"'"', M'"'"', Y'"'"') by first non-linear function of monotone increase, with derivative thereof being also of monotone increase,

d) converting the signals (C'"'"', M'"'"', Y'"'"') into signals (C",M",Y") by linear matrix calculation, and

e) further subjecting said signals (C",M",Y") to non-linear conversion into ink density signals (C,M,Y) to be used for recording by second non-linear function of monotone increase, with derivative thereof being of monotone decrease, which is of an inverse function of said first non-linear function,

wherein steps a) through e) are performed sequentially,

whereby the ink density is controlled according to said ink density signals (C,M,Y) for effecting color recording.

2. A color image forming apparatus which comprises:

a luminance matrix means for converting three primary color luminance signals (R,G,B) of additive color luminance signals, into second luminance signals (R'"'"', G'"'"', B'"'"') through matrix conversion,

a complementary color converting means, coupled in series with the luminance matrix means, for converting each color of said second luminance signals (R'"'"', G'"'"', B'"'"') into three primary color density signals (D_R, D_G, D_B) of subtractive color mixture,

a first converting means, coupled in series with the complementary color converting means, for said three primary color density signals (D_R, D_G, D_B) to non-linear conversion by first non-linear function of monotone increase, with derivative thereof being also of monotone increase,

a matrix means, coupled in series with the first converting means, for effecting matrix calculation by receiving outputs (C'"'"', M'"'"', Y'"'"') of said first converting means as inputs so as to output signals (C"M"Y") and

a second converting means, coupled in series with the matrix means, for subjecting said signals (C",M",Y") to non-linear conversion into ink density signals (C,M,Y) by second non-linear function of monotone increase, with derivative thereof being of monotone decrease, which is of an inverse function of said first non-linear function, whereby the ink density is controlled according to said ink density signals (C,M,Y) for effecting said color recording.

3. A color image forming apparatus which comprises:

a memory means including ROM or RAM for storing ink density signals (C,M,Y) obtained by

a) subjecting three primary color luminance signals (R,G,B) of additive color mixture to matrix conversion by luminance matrix calculation into second luminance signals (R'"'"'G'"'"'B'"'"') and

b) subjecting each color of said second luminance signals (R'"'"', G'"'"', B'"'"') to complementary color conversion into three primary color density signals (D_R, D_G, D_B) of subtractive color mixture, and

c) subjecting each color of said three primary color density signals (D_R, D_G, D_B) to non-linear conversion into signals (C'"'"', M'"'"', Y'"'"') by first non-linear function of monotone increase, with derivative thereof being also of monotone increase, and

d) converting the signals (C'"'"', M'"'"', Y'"'"') into signals (C",M",Y") by matrix calculation, and

e) further subjecting said signals (C",M",Y") to non-linear conversion by second non-linear function of monotone increase, with derivative thereof being of monotone increase, which is of an inverse function of said first non-linear function,

wherein steps a) through e) are performed sequentially,

an address generating means which inputs each higher order bit of the three primary color luminance signals (R,G,B) for generating address to be applied to said memory means, and

an interpolation calculating means which performs interpolation calculation through employment of the ink control signal outputted from said memory means, and each lower order bit information of said three primary color luminance signals (R,G,B) to be recorded, thereby to determine ink density signals (C,M,Y) with respect to said three primary color luminance signals (R,G,B) to be recorded, whereby the color recording is effected according to said ink density signals (C,M,Y).

4. A color image forming apparatus which comprises:

a memory means including ROM or RAM for storing ink density signals (C,M,Y) obtained by

a) converting each color of γ

-corrected luminance signals (R",G",B") of CRT into three primary color luminance signals (R,G,B) by a CRT inverse γ

correcting calculating step, and

b) converting said three primary color luminance signals (R,G,B) into second luminance signals (R'"'"', G'"'"', B'"'"') by a luminance matrix calculation, and

c) converting each color of said second luminance signals (R'"'"', G'"'"', B'"'"') into three primary color density signals (D_R, D_G, D_B) of subtractive color mixture by a complementary color conversion, and

d) subjecting each color of said three primary color density signals (D_R, D_G, D_B) to non-linear conversion into signals (C'"'"', M'"'"', Y'"'"') by first non-linear function of monotone increase, with derivative thereof being also of monotone increase, and

e) converting the signals (C'"'"', M'"'"', Y'"'"') into signals (C",M",Y") by matrix calculation, and further subjecting said signals (C",M",Y") to non-linear conversion by second non-linear function of monotone increase, with derivative thereof being of monotone decrease, which is of an inverse function of said first non-linear function,

wherein steps a) through e) are performed sequentially,

an address generating means which inputs each higher order bit of the γ

-corrected luminance signals (R",G",B") to be recorded for generating address to be applied to said memory means, and

an interpolation calculating means which performs interpolation calculation through employment of the ink density signals outputted from said memory means, and each lower order bit information of said CRT γ

-corrected luminance signals (R",G",B") to be recorded, thereby to determine ink density signals (C,M,Y) with respect to said CRT γ

-corrected luminance signals (R", G", B") to be recorded, whereby the color recording is effected according to said ink density signals (C,M,Y).

5. A method of determining correction factor including a luminance matrix factor to be employed in a luminance matrix calculation for converting three primary color luminance signals (R,G,B) into second luminance signals (R'"'"', G'"'"', B'"'"'), and a color correction factor to be employed in a color correcting calculation for converting three primary color density signals (D_R, D_G, D_B) into ink density signals (C,M,Y) to be used for recording, said method comprising:

a color chip signal generating step for generating n sets of ink density signals (Cj,Mj,Yj) (where j=1-n, n is a natural number),

a color chip forming step for forming n sets of color chips by controlling ink density through employment of said ink density signals (Cj,Mj,Yj),

a color measuring step for measuring color of said color chips,

an inverse color correcting calculating step for converting the ink density signals (Cj,Mj,Yj) into the three primary color density signals (D_R j,D_G j,D_B j) by an inverse color correcting calculation which is an inverse function of said color correcting calculation,

an inverse complementary color converting step for effecting the inverse complementary color conversion with respect to each color of said three primary color density signals (D_R j,D_G j,D_B j) for conversion into second luminance signals (R'"'"'j, G'"'"'j, B'"'"'j),

an inverse luminance matrix calculating step for converting said second luminance signals (R'"'"'j, G'"'"'j, B'"'"'j) into the three primary color luminance signals (Rj,Gj,Bj) by inverse luminance matrix calculation which is an inverse function of said luminance matrix calculation,

an evaluation value calculating step for calculating evaluation value through employment of the color measuring result of the color chips obtained by said color measuring step and the three primary color luminance signals (Rj,Gj,Bj) obtained by said inverse luminance matrix calculating step,

a converging calculation step which judges whether or not the evaluation value which is the output of said evaluation calculating step is the minimum, and effects renewal of the inverse color correction factor to be used for the inverse color correcting calculating and the inverse matrix factor to be used for the inverse matrix calculation according to the result of said judgement, thereby to output the inverse color correction factor and the inverse luminance matrix factor for minimizing said evaluation value, and

an inverse function calculating step for calculating the color correction fact or and luminance matrix factor by calculating inverse functions of the inverse color correction factor for minimizing said evaluation value, the inverse color correcting calculation employing the inverse luminance matrix factor, and the inverse luminance matrix calculating respectively.