Image's chromatism correction apparatus

Abstract

A reference pixel is specified for a specified pixel whose (luminance) value is below a threshold, for example, in RGB data obtained by an image pickup operation. The reference pixel should be on a straight line passing through the specified pixel and a center of the image and spaced from the specified pixel by a distance depending on a reduction or expansion rate of a blue (B) component image of the optical image corresponding to an optical zoom magnification in the image pickup. Only when the B value of the specified pixel is greater than that of the reference pixel, the B value of the specified pixel is replaced with that of the reference pixel. By expanding or reducing the blue component image alone for the original RGB data, image data is obtained in which the magnification chromatism is corrected.

1 . A chromatism correction apparatus for correcting a chromatism occurring in image data picked up by an image pickup device through an optical system, the apparatus comprising:
 identifying means for identifying a pixel in the image data having a luminance value below a luminance threshold;   reference pixel setting means for selecting and setting a reference pixel in the image data at a position on a straight line passing through the identified pixel and a center of the image based on a characteristic of the chromatism of the optical system;   comparing means for comparing a pixel value of a predetermined color component of the identified pixel with a pixel value of a same color component of the reference pixel; and   converting means, responsive to a comparison result of the comparing means, for converting the pixel value of the predetermined color component of the identified pixel to a different pixel value based on the pixel value of the same color component of the reference pixel.   
     
     
         2 . The apparatus according to  claim 1 , wherein the converting means converts the pixel value of the predetermined color component of the identified pixel to the different pixel value when the comparing means determines that the pixel value of the predetermined color component of the identified pixel is greater than the pixel value of the same color component of the reference pixel. 
     
     
         3 . The apparatus according to  claim 1 , wherein the converting means replaces the pixel value of the predetermined color component of the identified pixel with the pixel value of the same color component of the reference pixel. 
     
     
         4 . The apparatus according to  claim 1 , further comprising:
 characteristic acquiring means for acquiring information on a characteristic of a chromatism of the optical system;   wherein the converting means converts the pixel value of the predetermined color component of the identified pixel to the different pixel value depending on the characteristic of the chromatism indicated by the information acquired by the characteristic acquiring means.   
     
     
         5 . The apparatus according to  claim 4 , wherein the optical system is replaceable in the apparatus. 
     
     
         6 . The apparatus according to  claim 4 , wherein the characteristic acquiring means acquires characteristic information incidental to the image data. 
     
     
         7 . The apparatus  claim 1 , wherein the converting means performs the converting using only pixel values of pixels on the straight line passing through the identified pixel and the center of the image. 
     
     
         8 . A digital camera for correcting a chromatism on image data picked up by an image pickup device through an optical system, the camera comprising:
 identifying means for identifying a pixel in the image data having a luminance value below a luminance threshold;   reference pixel setting means for selecting and setting a reference pixel in the image data at a position on a straight line passing through the identified pixel and a center of the image based on a characteristic of the chromatism of the optical system;   comparing means for comparing a pixel value of a predetermined color component of the identified pixel with a pixel value of a same color component of the reference pixel; and   converting means, responsive to a comparison result of the comparing means, for converting the pixel value of the predetermined color component of the identified pixel to a different pixel value based on the pixel value of the same color component of the reference pixel.