Method of processing image signal by optical gamma correction curve and apparatus for performing the same

A method of effecting a gamma correction for an input image signal generated by an image signal generating device and supplying an output image signal to an image output device, said method comprising the following steps:

• (a) generating an output image signal by processing a plurality of known output data signal values in accordance with a linear characteristic curve;
• (b) forming an image on a record medium in accordance with the output image signal;
• (c) measuring a plurality of density values in said image;
• (d) interpolating said plurality of density values to derive all possible density values;
• (e) forming a density characteristic curve from the all possible density values;
• (f) deriving all possible output data signal values from the density characteristic curve;
• (g) forming a density characteristic data series representing a relationship between said all possible output data signal values and said all possible density values;
• (h) interpolating a plurality of denoted gamma characteristic data values to derive all possible denoted gamma characteristic data values;
• (i) forming a look-up table from said all possible denoted gamma characteristic data values and said density characteristic data series;
• (j) forming a denoted gamma correction curve from said look-up table;
• (k) selecting one of a previously prepared plurality of fine correction curves;
• and
• (l) forming an optimal gamma correction curve as a product between said denoted gamma correction curve and said one of said previously prepared plurality of fine correction curves selected in step (k).

An image signal processing apparatus for effecting a gamma correction for an input image signal and supplying an output image signal to an image output device, said apparatus comprising:

• data input means for entering (a) a plurality of known output data signal values, (b) a plurality of density values formed by the image output device in response to said plurality of known output data signals, and (c) a plurality of denoted density values;
• density curve forming means for forming a density curve representing a relationship between said plurality of known output data signal values and said plurality of density values;
• gamma correction curve forming means for forming a denoted gamma correction curve from said plurality of denoted density values by utilizing said density curve;
• and
• adjusting means for finely adjusting said denoted gamma correction curve in accordance with a fine correction curve selected from a plurality of previously prepared fine correction curves.