Oncolytic virotherapy of cancer with vesicular stomatitis virus

A color image encoder comprises a block converter for dividing a digital color video signal, which is composed of a Y signal and R-Y and B-Y signals, into blocks for the respective signals; an orthogonal transformer for orthogonally transforming the digital image video signal divided into the blocks, for each block, to produce orthogonal transform coefficients; a quantizer for quantizing the orthogonal transform coefficients; a variable length encoder for coding the quantized orthogonal transform coefficients to produce a code sequence; a generator code length counter for counting the length of the code sequence; a chrominance signal inspection circuit for calculating an absolute value of a difference between an average of pixel values in each block of at least one of the two chrominance signals and a value in an achromatic level of the chrominance signal, detecting a maximum value from the absolute values obtained in a unit of a collection of pixels for which a quantization scale used in the quantizer is to be changed, and comparing the maximum value with a prescribed threshold value; and a quantization scale decision circuit for providing a real quantization scale used in the quantizer on the basis of the length of the code sequence counted by the generator code length counter when the chrominance signal inspection circuit judges that the maximum value is smaller than the threshold value, and providing a real quantization scale used in the quantizer so that it becomes smaller than the interim quantization scale which is obtained on the basis of the length of the code sequence counted by the generator code length counter when the chrominance signal inspection circuit judges that the maximum value is larger than the threshold value. Therefore, a block for which the quantization scale is to be made small can be selected by a simple threshold setting for the chrominance signal, whereby visually conspicuous deterioration of image quality can be reduced.