Image-dependent color correction using black point and white point in a natural scene pictorial image

Claim 3

The method as described in claim 1, wherein there are three separations.

Claim 4

The method as described in claim 2, wherein the three separations correspond to the color primaries red, green and blue.

Claim 5

The method as defined in claim 1, wherein the color closest to white is the combination of signals S sep (m,n) in the image having the largest minimum signal.

Claim 6

The method as defined in claim 1, wherein the color closest to black is the combination of signals S sep (m,n) in the image having the smallest maximum signal.

Claim 7

The method as defined in claim 1, wherein the modifying step includes the following substeps: calculating for each possible intensity signal in each separation a modified intensity signal; storing the modified intensity signals in an addressable look-up table in memory; receiving intensity signals S sep (m,n) as addresses to the look-up table; and directing modified intensity signals to an the output step.

Claim 8

The method as defined in claim 1, where the color white is identified from a set of combined signals S sep (m,n) which do not include maximum system values.

Claim 9

The method as defined in claim 1, where the color black is identified from a set of combined signals S sep (m,n) which do not include minimum system values.

Claim 12

The apparatus as described in claim 9, wherein there are three separations.

Claim 13

The apparatus as described in claim 10, wherein the three separations correspond to the color primaries red, green and blue.

Claim 14

The apparatus as defined in claim 9, wherein the color closest to white is the combination of signals S sep (m,n) in the image having the largest minimum signal.

Claim 15

The apparatus as defined in claim 9, wherein the color closest to black is the combination of signals S sep (m,n) in the image having the smallest maximum signal.

Claim 16

The apparatus as defined in claim 9, wherein the modifying means includes: means for calculating for each possible intensity signal in each separation a modified intensity signal; means for storing the result in an addressable look-up table in memory; means for receiving intensity signals S sep (m,n) as addresses to the look-up table; and means for directing modified intensity signals to an output step.

Claim 17

The apparatus as defined in claim 9, wherein the modifying means modifies each intensity signal S sepN (m,n) forming the separation with a function: ##EQU3## Where Sep in is a single input intensity signal in S sepN (m,n) in a selected one of the N separations, Sep out is a single output intensity signal corresponding to Sep in in S sepN (m,n) in the selected separation, Sep max is the selected separation signal in the combination of signals S sepN (m,n) in the image providing the color closest to white, Sep max is the selected separation signal in the combination of signals S sepN (m,n) in the image providing the color closest to black.

Claim 18

A color reproduction system system, including color correction, for reproduction of natural scene original images in which the color is undesirably shifted including: a color image scanner, producing from a scanned natural scene original document in which the color is undesirably shifted, a set of electronic signals in a format providing a plurality of N separations describing intensity for N color primaries within the image, each separation formed by a plurality of separation intensity signals S sepN (m,n) for discrete areas therein, whereby color for a discrete area in the image is a combined output response of separation intensity signals S sepN (m,n) for the corresponding area m,n in the image from each of the N separations; a separation maximum detector receiving as an input the separation intensity signals S sepN (m,n) for the image and producing as an output a set of N separation intensity signals S sep1max . . . S sepNmax representing an unsaturated color in the image closest to white and a maximum separation intensity signal W max thereof; a separation minimum detector receiving as an input the separation intensity signals S sepN (m,n) for the image and producing as an output a set of N separation intensity signals S sep1min . . . S sepNmin representing a color in the image closest to black and a minimum separation intensity signal W min thereof; a shift correction calculation circuit, calculating for each possible intensity signal in each separation 1 . . . N a modified intensity signal as a function of the separation signal S sepN (m,n) in the color closest to white, the separation signal S sepM (m,n) in the color closest to black, W min and W max ; a device memory receiving said set of corrected separation intensity signals in a table for each separation, addressable by a separation intensity value from the color scanner; an output reproduction device, operative responsive to the corrected signals in each of N separation to produce a color response.

Claim 19

A color reproduction system system, including color correction, for reproduction of natural scene original images in which the color is undesirably shifted including: a color image scanner, producing from a scanned natural scene original document in which the color is undesirably shifted, a set of electronic signals in a format providing a plurality of N separations describing intensity for N color primaries within the image, each separation formed by a plurality of separation intensity signals S sepN (m,n) for discrete areas therein, whereby color for a discrete area in the image is a combined output response of separation intensity signals S sepN (m,n) for the corresponding area m,n in the image from each of the N separations; a separation maximum detector receiving as an input the separation intensity signals S sepN (m,n) for the image and producing as an output a set of N separation intensity signals S sep1max . . . S sepNmax representing an unsaturated color in the image closest to white and a maximum separation intensity signal W max thereof; a separation minimum detector receiving as an input the separation intensity signals S sepN (m,n) for the image and producing as an output a set of N separation intensity signals S sep1min . . . S sepNmin representing a color in the image closest to black and a minimum separation intensity signal W min thereof; a shift correction calculation circuit, calculating for each possible intensity signal in each separation 1 . . . N a modified intensity signal as a function of the separation signal S sepN (m,n) in the color closest to white, the separation signal S sepM (m,n) in the color closest to black, W min and W max ; a device memory receiving said set of corrected separation intensity signals in a table for each separation, addressable by a separation intensity value from the color scanner; an output reproduction device, operative responsive to the corrected signals in each of N separation to produce a color response.

Claim 20

The device as defined in claim 16, wherein there are three separations.

Claim 21

The device as described in claim 17, wherein the three separations correspond to the color primaries red, green and blue.

Claim 22

The apparatus as defined in claim 16, wherein the color closest to white is the combination of signals S sepN (m,n) in the image having the largest minimum signal.

Claim 23

The apparatus as defined in claim 16, wherein the color closest to black is the combination of signals S sepN (m,n) in the image having the smallest maximum signal.

Claim 24

The apparatus as defined in claim 16, wherein the calculating includes: a calculating circuit deriving a modification for each possible intensity signal in each separation a modified intensity signal; an addressable memory storing the result in a look-up table; a storage control arrangement for storing calculated values to the addressable memory and directing modified intensity signals to an output step.

Claim 25

A color reproduction system including color correction for reproduction of electronically encoded natural scene original images in which the color is undesirably shifted including: a color image scanner, producing from a scanned original image S(m,n) in which the color is undesirably shifted, a set of electronic signals in a format providing separations describing intensity for red, green and blue colors, each separation formed by a plurality of intensity signals for discrete areas in the image, whereby color for a discrete area in the image is a combined output response of a triplet of intensity signals for a discrete area (m,n) from each separation R, G, B; a maximum detector receiving as an input the separation intensity signals from each separation and identifying as an image white point a triplet of intensity signals containing the color closest to white and one intensity signal W max of the triplet which is largest; a minimum detector receiving as an input the separation intensity signals from each separation and identifying as an image black point a triplet min containing the color closest to black and one intensity signal W min of the triplet which is largest; a color shift calculation circuit determining for each separation r, g, b a corrected intensity values in accordance with the function: ##EQU4## Where (R,G,B) in are single input intensity signals in a selected separations, (R,G,B) out are single output intensity signals corresponding to (R,G,B) in in a selected separation, (R,G,B) w is the corresponding separation signal in the color closest to white, (R,G,B) B is the corresponding separation signal in the color closest to black. an output reproduction device, operative responsive to the corrected signals (R,G,B) out (m,n)in each of the separations to produce a color response S'(n,m).

Claim 26

A color reproduction system including color correction for reproduction of electronically encoded natural scene original images in which the color is undesirably shifted including: a color image scanner, producing from a scanned original image S(m,n) in which the color is undesirably shifted, a set of electronic signals in a format providing separations describing intensity for red, green and blue colors, each separation formed by a plurality of intensity signals for discrete areas in the image, whereby color for a discrete area in the image is a combined output response of a triplet of intensity signals for a discrete area (m,n) from each separation R, G, B; a maximum detector receiving as an input the separation intensity signals from each separation and identifying as an image white point a triplet of intensity signals containing the color closest to white and one intensity signal W max of the triplet which is largest; a minimum detector receiving as an input the separation intensity signals from each separation and identifying as an image black point a triplet min containing the color closest to black and one intensity signal W min of the triplet which is largest; a color shift calculation circuit determining for each separation r, g, b a corrected intensity values in accordance with the function: ##EQU4## Where (R,G,B) in are single input intensity signals in a selected separations, (R,G,B) out are single output intensity signals corresponding to (R,G,B) in in a selected separation, (R,G,B) w is the corresponding separation signal in the color closest to white, (R,G,B) B is the corresponding separation signal in the color closest to black. an output reproduction device, operative responsive to the corrected signals (R,G,B) out (m,n)in each of the separations to produce a color response S'(n,m).