Color printer characterization using optimization theory and neural networks

A method for controlling a color printer having a color gamut, said color printer being responsive to a computer system that provides color space image signals that command said color printer to print an output print that corresponds to said color space image signals, the method comprising the steps of:

• producing a plurality of output prints from said color printer representative of the color gamut of said color printer and comprising a plurality of different colors selected in accordance with an ANSI print set in xy chromaticity coordinates;
• analyzing said plurality of output prints:
• providing a neural network;
• training said neural network using the results of said analysis step to thereby provide a gamut trained neural network;
• using said gamut trained neural network to produce a printer profile lookup table that correlates color space signals to the color gamut of said color printer;
• connecting said color space image signals to address said printer profile lookup table;
• and
• controlling said color printer in accordance with a portion of the color gamut of said color printer that corresponds to said color space image signals.

A method of making a profile lookup table for a CMYK color printer comprising the steps of:

• producing a relatively small number of different color prints using the CMYK printer;
• using said color prints to train a neural network and thereby define a gamut of the CMYK printer as said gamut is defined by said relatively small number of different color prints, said neural network comprising from about 5 to about 7 neurons;
• and
• using said trained neural network to generate a printer profile lookup table that converts LAB values to corresponding CMYK values in accordance with said gamut of the CMYK printer.

Apparatus for producing a profile lookup table for use by a CMYK color printer in producing color prints, the profile lookup table comprising a plurality of table entries wherein each entry comprises a LAB value and a corresponding CMYK value in accordance with a print gamut of the CMYK color printer, the apparatus comprising:

• a neural network defining the print gamut of the CMYK color printer;
• said neural network having an input for receiving a test CMYK value;
• said neural network having an output for generating a LAB value that corresponds to said print gamut and to said test CMYK value;
• an error determining network;
• said error determining network having a first input connected to receive a series of LAB values wherein each of said received LAB values corresponds to a table entry of the profile lookup table;
• said error determining network having a second input connected to said output of said neural network to receive test LAB values;
• said error determining network having an error output that is responsive to a difference in the LAB values received by said first and second inputs;
• an error testing network establishing a LAB error criteria as a function of C, M, Y and K variables;
• said error testing network having an input connected to said error output of said error determining network;
• said error testing network having a NO output indicative of failure of said error output of said error determining network to meet said LAB error criteria;
• said error testing network having a YES output indicative of said error output of said error determining network meeting said LAB error criteria;
• and
• said YES output providing a CMYK value table entry to the profile lookup table that corresponds to a LAB value then connected to said first input of said error determining network.

Apparatus for producing a profile lookup table for use by a color printer in producing color prints, the profile lookup table comprising a plurality of table entries wherein each entry comprises a printer independent color value and a corresponding printer dependent color value in accordance with a print gamut of the color printer, the apparatus comprising:

• a neural network defining the print gamut of the color printer;
• said neural network having an input for receiving a test printer dependent color value;
• said neural network having an output for generating a printer independent color value that corresponds to said print gamut and to said test printer dependent color value;
• an error determining network;
• said error determining network having a first input connected to receive a series of printer independent color values wherein each of said received printer independent color values corresponds to a table entry of the profile lookup table;
• said error determining network having a second input connected to said output of said neural network to receive test printer independent color values therefrom;
• said error determining network having an error output that is responsive to a difference in printer independent color values received by said first and second inputs;
• an error testing network establishing a color value error criteria;
• said error testing network having an input connected to said error output of said error determining network;
• said error testing network having a NO output indicative of failure of said error output of said error determining network to meet said color value error criteria;
• said error testing network having a YES output indicative of said error output of said error determining network meeting said color value error criteria;
• and
• said YES output providing a printer dependent color value table entry to the profile lookup table that corresponds to a printer independent color value then connected to said first input of said error determining network.

Apparatus for converting printer independent color signals to printer dependent color signals, comprising:

• an input for receiving a printer independent color signal that defines a color pixel image to be printed by a color printer;
• a color gamut conversion network having an input for receiving a test printer dependent color signal, and having an output for providing a test printer independent color signal in accordance with a color gamut of the color printer and in accordance with said received test printer dependent color signal;
• an error determining junction having a first input connected to said input receiving said printer independent color signal defining a color pixel image to be printed by the color printer, having a second input connected to said output of said color gamut conversion network for receiving said test printer independent color signal, and having an output responsive to a difference between said printer independent color signal defining a color pixel image to be printed by the color printer and said test printer independent color signal;
• a decision network constructed and arranged to implement a function f=C1(error signal)+C2(a parameter of a printed color pixel), wherein said terms “C1” and “C2” are constants, wherein said term “error signal” is a function of an acceptable color error of a printed color pixel corresponding to said printer independent color signal, and wherein said term “a parameter of a printed color pixel” relates to a factor, such as the ink cost of a printed color pixel corresponding to said input printer independent signal;
• said decision network having an input connected to said output of said error determining junction, having a YES output responding to said function being satisfied, and having a NO output responding to said function not being satisfied;
• a generating network for generating a test printer dependent color signal;
• said generating network having an input connected to said NO output of said decision network, and said generating network operating to generate said test printer dependent signal on an output of said generating network in response to said function not being satisfied;
• and
• circuit means connecting said output of said generating network to said input of said color gamut conversion network.

A method for converting an input color signal to an output color signal that correspond to the color gamut of a color printer, comprising the steps of:

• receiving said input color signal;
• providing color gamut conversion means for generating a test color signal for comparison to said input color signal, said test color signal being in accordance with said color gamut of said color printer;
• providing error determining means for determining an error magnitude of a difference between said input color signal and said test color signal;
• providing decision means responsive to said error magnitude, said decision means operating to determine an acceptable error or an unacceptable error;
• providing first means responsive to said unacceptable error for controlling said color gamut conversion means to generate a different test color signal for comparison to said input color signal;
• repeating operation of said first means until a given test color signal results in an acceptable error being determined by said decision means;
• and
• providing second means responsive to said acceptable error for generating said output color signal in accordance with said given test color signal.

Apparatus for constructing a profile lookup table for use by a given CMYK printer in printing a CMYK color print in response to a plurality of printer independent color signals that define the CMYK color print, the profile lookup table containing a plurality of individual entries, each entry containing a printer independent signal and a corresponding CMYK signal in accordance with a gamut of the given CMYK printer, the profile lookup table for use in converting printer independent signals to CMYK signals in accordance with the gamut of the given CMYK printer, said apparatus comprising:

• a neural network having an input and an output;
• said neural network being responsive to a CMYK signal at said input and operating to provide a printer independent signal at said output in accordance with the gamut of the given CMYK printer;
• apparatus input means for receiving a plurality of input printer independent signals, each individual one of said input printer independent signals corresponding to an individual entry in the profile lookup table;
• error measuring means having a first input connected to receive an individual one of said plurality of input printer independent signals, having a second input connected to said output of said neural network, and having a difference error output that is responsive to a difference between signals applied to said first and second inputs;
• error criteria means having an input connected to said difference error output of said error measuring means, said error criteria means operating to set CMYK optimization criteria to be met by all CMYK entries to the profile lookup table;
• said error criteria means providing a NO output so long as said difference between signals applied to said first and second inputs of said error measuring means does not satisfy said CMYK optimization criteria;
• said error criteria means providing a YES output when said difference between signals applied to said first and second inputs of said error measuring means satisfies said CMYK optimization criteria;
• first means responsive to said NO output operating to sequentially apply a different CMYK signal to said input of said neural network until such time as a given CMYK signal applied to said input of said neural network operates to provide said YES output from said error criteria means;
• and
• second means responsive to said YES output for producing an entry in the profile lookup table that comprises said individual one of said input printer independent signal and said given CMYK signal.

Apparatus for controlling a given CMYK printer to print a CMYK color print in response to a plurality of printer independent color signals that define a plurality of color pixels within the CMYK color print, said CMYK printer having a CMYK color gamut, said apparatus comprising:

• gamut-defining means having an input and an output;
• said gamut-defining means being responsive to a CMYK signal at said input and operating to provide a printer independent signal at said output in accordance with the CMYK gamut of the given CMYK printer;
• apparatus input means for receiving the plurality of input printer independent signals that define a plurality of pixels within the CMYK color print, each individual one of said input printer independent signals corresponding to an individual pixel of the pixels within the CMYK color print;
• error measuring means having a first input connected to receive each individual one of said plurality of input printer independent signals, having a second input connected to said output of said gamut-defining means, and having a difference error output that is responsive to a difference between signals applied to said first and second inputs;
• error criteria means having an input connected to said difference error output of said error measuring means, said error criteria means operating to set CMYK optimization criteria to be met by all color pixels of the CMYK color print;
• said error criteria means providing a NO output so long as said difference between signals applied to said first and second inputs of said error measuring means does not satisfy said CMYK optimization criteria;
• said error criteria means providing a YES output when said difference between signals applied to said first and second inputs of said error measuring means satisfies said CMYK optimization criteria;
• first means responsive to said NO output operating to sequentially apply a different CMYK signal to said input of said gamut-defining means, until such time as a given CMYK signal applied to said input of said gamut-defining means operates to provide said YES output from said error criteria means;
• and
• second means responsive to said YES output for providing said given CMYK signal to control the given printer.