PURPOSE: To obtain a color picture processing device excellent in color reproducibility by forming a prescribed picture data based on a reading signal from a reader.

CONSTITUTION: In a system where a reader 4 reads a picture printed out after a prescribed picture data is outputted from a pattern generator 1 and printed out, an LUT is constituted so that the picture is converted into the original picture data by using the read picture data as addresses. Thus, it is not so simply executed to write all data (e.g., 643) in the LUT, because data quantity is too much practically. Then the picture data generated from the pattern generator 1 is thinned properly, and the LUT is written according to the thinned picture data and other addresses of the LUT not written are interpolated afterward, allowing to write data to all the addresses of the LUT.