1. An image processing method, comprising: transforming a set of color image signals representing an original image into a luminance signal and color difference signals; transforming the luminance signal and the color difference signals separately into multi-resolution signals of the level 1 to the level N to make them luminance multi-resolution signals and color difference multi-resolution signals; applying an inverse multi-resolution transform to the color difference multi-resolution signals to make them processed color difference signals, after suppressing the high-frequency components of the level 1 of the color difference multi-resolution signals; applying an inverse multi-resolution transform processing to the luminance multi-resolution signals to make them a processed luminance signal, after applying a coring processing using a condition for each level different from other levels to the high-frequency signals of each level of the luminance multi-resolution signals; transforming the processed luminance signal and the processed color difference signals into a set of processed color image signals.