Contrast correcting apparatus

Claim 1

An apparatus for correcting contrast of a particular region selected from an original image, comprising: original image data storage means for storing RGB signals which are digitized three primary signals of pixels in said original image; a Lab conversion table for converting said RGB signals to lightness index L and perceived chromaticity indexes a and b of CIE-Lab perceived color space; processing condition designating means for designating a color to be corrected and to act as a central object of contrast correction processing, for designating an effective range of the contrast correction processing with a distance in said perceived color space and with reference to said color to be corrected, and for designating a characteristic parameter for the contrast correction processing; a lookup table assigned to each of said RGB signals for contrast correction of said pixels in said original image, for storing RGB output data resulting from a contrast correction, in relation to RGB input data of said RGB signals applied as addresses; lookup table initializing means for setting said RGB output data corresponding to said RGB input data to said lookup table, such that input and output values match for RGB output data pairing with RGB input data corresponding to said color to be corrected, and that data derived from said characteristic parameter with reference to a matching point between said RGB input data and said RGB output data relating to said color to be corrected are set for RGB output data corresponding to other RGB input data; and output control means for deriving a separating distance in said perceived color space from Lab values of said color to be corrected and Lab values of each said pixels in said original image successively received from said Lab conversion table, said output control means being operable, when said separation distance is smaller than said distance used in designating said effective range, to determine said pixels to be subjected to said contrast correction processing and validate said RGB output data from said lookup table; and when said separating distance is larger than said distance used in designating said effective range, to determine said pixels to be excluded from said contrast correction processing and output said RGB signals of said original image intact, wherein said processing condition designating means is operable to designate a gradient of an input/output conversion characteristic expressed by a linear expression of said lookup table, as said characteristic parameter for the contrast correction processing.

Claim 2

An apparatus for correcting contrast of a particular region selected from an original image, comprising: original image data storage means for storing RGB signals which are digitized three primary signals of pixels in said original image; a Lab conversion table for converting said RGB signals to lightness index L and perceived chromaticity indexes a and b of CIE-Lab perceived color space; processing condition designating means for designating a color to be corrected and to act as a central object of contrast correction processing, for designating an effective range of the contrast correction processing with a distance in said perceived color space and with reference to said color to be corrected, and for designating a characteristic parameter for the contrast correction processing; a lookup table assigned to each of said RGB signals for contrast correction of said pixels in said original image, for storing RGB output data resulting from a contrast correction, in relation to RGB input data of said RGB signals applied as addresses; lookup table initializing means for setting said RGB output data corresponding to said RGB input data to said lookup table, such that input and output values match for RGB output data pairing with RGB input data corresponding to said color to be corrected, and that data derived from said characteristic parameter with reference to a matching point between said RGB input data and said RGB output data relating to said color to be corrected are set for RGB output data corresponding to other RGB input data; and output control means for deriving a separating distance in said perceived color space from Lab values of said color to be corrected and Lab values of each said pixels in said original image successively received from said Lab conversion table, said output control means being operable, when said separation distance is smaller than said distance used in designating said effective range, to determine said pixels to be subjected to said contrast correction processing and validate said RGB output data from said lookup table; and when said separating distance is larger than said distance used in designating said effective range, to determine said pixels to be excluded from said contrast correction processing and output said RGB signals of said original image intact, wherein said processing condition designating means is operable to designate a gradient of an input/output conversion characteristic expressed by a linear expression of said lookup table, as said characteristic parameter for the contrast correction processing.

Claim 11

An apparatus for correcting contrast of a particular region selected from an original image, comprising: original image data storage means for storing RGB signals which are digitized three primary signals of pixels in said original image; an HSL conversion table of converting said RGB signals to values of hue (H), saturation (S) and lightness (L) which are three attributes of perceived color; processing condition designating means for designating a color to be corrected and to act as a central object of contrast correction processing, for designating effective ranges of the contrast correction processing with HSL values and with references to said color to be corrected, and for designating a characteristic parameter for the contrast correction processing; a lookup table assigned to each of said RGB signals for contrast correction of said pixels in said original image, for storing RGB output data resulting from a contrast correction, in relation to RGB input data of said RGB signals applied as addresses; lookup table initializing means for setting said RGB output data corresponding to said RGB input data to said lookup table, such that input and output values match for RGB output data pairing with RGB input data corresponding to said color to be corrected, and that data derived from said characteristic parameter with reference to a matching point between said RGB input data and said RGB output data relating to said color to be corrected are set for RGB output data corresponding to other RGB input data; and output control means for deriving differences, respectively, between HSL values of said color to be corrected and HSL values of said pixels in said original image successively received from said HSL conversion table, said output control means being operable, when said differences are smaller than said effective ranges, respectively, to determine said pixels to be subjected to said contrast correction processing and validate said RGB output data from said lookup table, and when any one of said differences is larger than a corresponding one said effective ranges, to determine said pixels to be excluded from said contrast correction processing and output said RGB signals of said original image intact, wherein said processing condition designating means is operable to designate a gradient of an input/output conversion characteristic expressed by a linear expression of said lookup table, as said characteristic parameter for the contrast correction processing.

Claim 12

An apparatus for correcting contrast of a particular region selected from an original image, comprising: original image data storage means for storing RGB signals which are digitized three primary signals of pixels in said original image; an HSL conversion table of converting said RGB signals to values of hue (H), saturation (S) and lightness (L) which are three attributes of perceived color; processing condition designating means for designating a color to be corrected and to act as a central object of contrast correction processing, for designating effective ranges of the contrast correction processing with HSL values and with references to said color to be corrected, and for designating a characteristic parameter for the contrast correction processing; a lookup table assigned to each of said RGB signals for contrast correction of said pixels in said original image, for storing RGB output data resulting from a contrast correction, in relation to RGB input data of said RGB signals applied as addresses; lookup table initializing means for setting said RGB output data corresponding to said RGB input data to said lookup table, such that input and output values match for RGB output data pairing with RGB input data corresponding to said color to be corrected, and that data derived from said characteristic parameter with reference to a matching point between said RGB input data and said RGB output data relating to said color to be corrected are set for RGB output data corresponding to other RGB input data; and output control means for deriving differences, respectively, between HSL values of said color to be corrected and HSL values of said pixels in said original image successively received from said HSL conversion table, said output control means being operable, when said differences are smaller than said effective ranges, respectively, to determine said pixels to be subjected to said contrast correction processing and validate said RGB output data from said lookup table, and when any one of said differences is larger than a corresponding one said effective ranges, to determine said pixels to be excluded from said contrast correction processing and output said RGB signals of said original image intact, wherein said processing condition designating means is operable to designate a gradient of an input/output conversion characteristic expressed by a linear expression of said lookup table, as said characteristic parameter for the contrast correction processing.