To provide an image coder by which an image signal is efficiently compressed so as to suppress a deterioration in an image while suppressing amount of arithmetic operation.
A difference from a predicted value of a preceding frame of a frame memory section 611 with respect to a small block being division of image data of a processing object image signal 602. After an orthogonal transformation coefficient obtained through transformation for each orthogonal transformation block consisting of a difference is quantized and a code is assigned and the result is sent via a frame buffer section 615. Then an evaluation value calculation section 604 to obtain an evaluation value based on the difference in the orthogonal transformation block is provided and the number of arithmetic operations of the orthogonal transformation coefficient in the case of orthogonal transformation is obtained for each block by an arithmetic operation number calculation section 605 and number of the orthogonal transformation coefficients calculated by the orthogonal transformation section 607 is controlled for each block based on the evaluation value. The orthogonal transformation section 607 obtains the designated number of orthogonal transformation coefficients sequentially from low-degrees for each block so as to reduce an arithmetic operation amount for highdegrees not giving much effect onto the image quality.
ISHIBASHI SATOSHI
YASHIMA YOSHIYUKI
KODERA HIROSHI
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