Adaptive image coding considering the chroma format

The present invention is directed to an image information encoding apparatus adapted for performing intra-image encoding on the basis of resolution of color components and color space of an input image signal. In the image information encoding apparatus (10), an intra prediction unit (23) serves to adaptively change block size in generating a prediction image on the basis of a chroma format signal indicating whether resolution of color components is that of any one of 4:2:0 format, 4:2:2 format and 4:4:4 format, etc., and a color space signal indicating whether color space is any one of YCbCr, RGB and XYZ, etc. In addition, an orthogonal transform unit (14) and a quantization unit (15) serve to also change orthogonal transform technique and quantization technique in accordance with the chroma format signal and the color space signal. A reversible encoding unit (16) encodes the chroma format signal and the color space signal to include the encoded signals thus obtained into image compressed information.