Brightness-variation compensation method and coding/decoding apparatus for moving pictures

A moving image coding apparatus, comprising:

• parameter determining means for determining a parameter DB indicating a gain change and a parameter DC indicating a contrast change, the parameters representing overall luminance changes between a reference image plane and an image plane being processed, and being determined by using differences in luminance values between corresponding pixels in the reference image plane and the image plane being processed,
• wherein said parameter determining means determines the parameters DB and DC for the entire image plane being processed using the two parameters DC and DB for each of n blocks in the image plane being processed, n being an integer of at least 2 and each of n blocks composed of K×L pixels, K and L being natural numbers, and
• taking the pair of parameters DB and DC for each of n blocks which are most frequent as the parameters DB and DC of the entire image plane being processed;
• and
• a brightness variation compensation means for correcting a luminance value x of each pixel in said image plane being processed using said parameters DB and DC according to the formula DC.x+DB.

A computer-readable recording medium recording a moving image coding program, said moving image coding program containing instructions for a computer to execute:

• a parameter determining step of determining a parameter DB indicating a gain change and a parameter DC indicating a contrast change, the parameters representing overall luminance changes between a reference image plane and an image plane being processed, and being determined by using differences in luminance values between corresponding pixels in the reference image plane and the image plane being processed;
• wherein said parameter determining step includes determining the parameters DB and DC for the entire image plane being processed using the two parameters DC and DB for each of n blocks in the image plane being processed. n being an integer of at least 2 and each of n blocks composed of K×L pixels, K and L being natural numbers, and
• taking the pair of parameters DB and DC for each of n blocks which are most frequent as the parameters DB and DC of the entire image plane being processed;
• and
• a brightness variation compensation step of correcting a luminance value x of each pixel in said image plane being processed using said parameters DB and DC according to the formula DC.x+DB.

A computer-readable recording medium recording coded data of moving images, wherein said coded data includes a plurality of areas recording image plane coded data encoded by units of image planes, said areas recording image plane coded data comprising:

• a parameter area recording parameters DB indicating gain changes and DC indicating contrast changes, the parameters representing overall luminance changes between reference image planes and image planes being processed, and being determined by using differences in luminance values between corresponding pixels in the reference image plane and the image plane being processed;
• wherein the parameters DB and DC recorded in the parameter area are determined by using the two parameters DC and DB obtained from each of n blocks in the image plane being processed, n being an integer of at least 2 and each of n blocks composed of K×L pixels, K and L being natural numbers, and
• taking the pair of parameters DB and DC for each of n blocks which are most frequent as the parameters DB and DC of the entire image plane being processed;
• and
• a coded area recording data in units of image planes relating to differences in pixel values for corresponding pixels between said reference image planes and image planes wherein luminance values x of the pixels in said reference image planes have been corrected by using the parameters DB and DC according to the formula DC.x+DB.