IMAGE SIGNAL ENCODER, IMAGE SIGNAL ENCODING METHOD, IMAGE SIGNAL DECODER, AND IMAGE SIGNAL DECODING METHOD

PROBLEM TO BE SOLVED: To provide an image signal encoder which can suppress an error when an image signal is encoded and decoded without reducing reduction effect of data capacity.SOLUTION: A gain normalization section 12 normalizes a gain for arranging ranges of data, which a plurality of pieces of color data having the first number of bits take, so that the gain to the color data of a small value becomes a large value to generate normalized gain data with the gain to the color data taking the maximum value as reference. Encoding sections 14R, 14G, and 14B encode the color data taking the maximum value into the second number of bits smaller than the first number of bits by using a quantization table which is previously held and encode the color data except for the color data taking the maximum value into the second number of bits by using an adjusted quantization table obtained by dividing a value of the quantization table which is previously held by a normalized gain which the normalized gain data shows.