IMAGE DISPLAY DEVICE

PURPOSE:To reproduce gradation without damaging the features of a source image by avoiding picture quality degradation such as forming a pseudo contour by executing non-linear transformation so that the density histogram of an output image displayed with the designated gradation can be uniform. CONSTITUTION:A CPU 1 of a histogram preparing means reads source image data from a RAM 3 of an image storage means and prepares the density histogram for each of three primary colors for each scanning line, and a histogram transforming means of the CPU 1 non-linearly transforms the respective gradation areas under the prescribed gradation and uniforms the density histogram in the respective gradation areas under the designated gradation for each of three primary colors. Then, the table preparing means of the CPU 1 prepares a look-up table, in which the average gradation value for each gradation area under the prescribed gradation non-linearly transformed by the histogram transforming means is made correspondent to the designated gradation, for each of three primary colors for each horizontal line. Thus, the density histogram is non-linearly transformed to be uniform.