General practice receptionists' attitudes and beliefs towards preventive medicine before and after training and support interventions

An apparatus for converting an image signal representing an image having gradation includes a first density histogram generator. The first density histogram generator generates a first density histogram based on a first image signal which is obtained by reading a data read region. Of peak portions formed in the first density histogram, the density rank value of a peak portion which satisfies a predetermined condition is detected. A pixel-to-be-removed detector determines pixels-to-be-removed whose average densities are included in a pixel removal density range which corresponds to the detected peak portion density rank value. A second density histogram is generated from the pixels remaining after the removal of the pixels-to-be-removed. Based on the second density histogram, a cumulative density histogram is generated to thereby find a highlight point and a shadow point through which a gradation curve passes. Then, the gradation curve is established and an image processing part converts the first image signal into a second image signal in accordance with the established gradation curve.