Gradation correction device and image sensing device therewith for supplying images with good gradation for both front-lit and back-lit objects

An image sensing device comprising:

• an image sensor, said image sensor detecting input picture signals of a picture and providing input digital picture signals;
• a feature quantity extractor, said feature quantity extractor for extracting feature quantities from the input digital picture signals of a picture, the feature quantities reflecting luminance level distribution of the input picture digital signals;
• a correction coefficient determinator, said correction coefficient determinator generating a correction coefficient which determines a gradation correction characteristic based on the feature quantities received from the feature quantity extractor, said gradation correction characteristic defining an output signal for an input signal;
• a gain generator, said gain generator generating a correction gain which changes with a signal level of an input digital luminance signal according to the luminance signal and the correction coefficient received from said correction coefficient determinator;
• and
• a corrector, said corrector correcting each of the input picture signals by multiplying each of the input digital picture signals by the correction gain generated by said gain generator.

A gradation correction device comprising:

• a feature quantity extraction means for extracting feature quantities from input digital picture signals of a picture, said feature quantities reflecting luminance level distribution of the input digital picture signals;
• a gradation correction characteristic determination means for determining a gradation correction characteristic based on the feature quantities received from the feature quantity extraction means, said gradation correction characteristic defining an output signal for an input signal;
• and
• a correction means for correcting each of the input digital picture signals by using the gradation correction characteristic determined by the gradation correction characteristic determination means;
• whereby the gradation correction characteristic for the input picture digital signals is varied according to features thereof;
• said correction means comprising:
• a correction gain generation means for generating a correction gain for the input digital picture signals according to the input digital picture signals and the correction coefficient determined by said gradation correction characteristic determination means;
• and
• a multiplication means for multiplying the input digital picture signals with the correction gain received from the correction gain generation means.