To automate the setting of more proper image processing conditions by selecting an input density of an area where a sum of weighting coefficients reaches a prescribed value or over as a highlight or shadow density and using it for output conversion in a highlight or shadow space in which the weighting coefficients are set smaller as being parted from the vicinity of a prescribed point.

The repetitive frequency of prescribed processing at highlight and shadow points by a skillful operator is stored in a weighting coefficient storage section 50 as truncated cone-shaped distribution data around the gray axis on the C/M/Y color space coordinate. An HL/SD space data extract section 48 receiving photometric equivalent medium density data C.M.Y from an original after preliminary scanning and image processing, extracts highlight or shadow space data, which are fed to a summing processing section 52. The summing processing section 52 applies weight summing to the data with a weighting coefficient from the weighting coefficient storage section 50 and gives the result to an HL/SD discrimination section 54. When the sum exceeds a threshold value, the HL/SD discrimination section 54 discriminates it to be presence of a highlight or shadow point.