Image signal processor

Abstract

A plurality of conversion characteristic functions 90, 92, and 94 used in a gamma correction circuit are stored in the processor in advance. A characteristic setting circuit sets standard characteristics 90 to the gamma correction circuit when exposure time E and a gain G are small. When E is large and G is small, change to correction characteristics 92 is made where inclination is set small at a low signal level, and amplification in a noise level at the low signal level is suppressed. When G is large, change to correction characteristics 94 having gentle inclination over a wider range than the characteristics 92 is made, and the amplification of the noise level that becomes larger in proportion to the G by gradation correction in the gamma correction circuit is suppressed.

Description

technical field [0001] The present invention relates to an image signal processing device that performs gradation correction of an image signal, and particularly relates to control of noise in gradation correction processing based on nonlinear characteristics. Background technique [0002] As one of the image qualities of an imaging device such as a digital camera, there is gradation, and a gradation correction circuit for correcting it is generally provided. The gradation correction circuit converts the signal level of the input image signal according to a predetermined conversion characteristic function, and outputs the converted image signal. For example, a gamma correction circuit is also a circuit for gradation correction. [0003] image 3 is a schematic curve showing the transformation characteristics. The transformation characteristic is generally nonlinear, and in the part of the transformation characteristic curve whose slope is greater than 1, the gray scale is ...

AI Technical Summary

Problems solved by technology

However, if the gains of AGC and DGC are increased, disturbances such as random disturbances contained in image signals are also amplified

In addition, if the exposure time is prolonged, the level of dark current contained in the image signal increases, and the level of interference caused by this also increases

Therefore, in this case, as image 3 As shown in the characteristic curve 1 of , there is a problem that the degradation of S / N may become conspicuous in a gradation correction circuit that has a conversion characteristic that has a steep gradation in a low signal area.

[0007] On the other hand, in order to suppress S / N degradation, the transformation characteristic function is changed to an S-shaped γ characteristic, or the gradation correction is set to suppress the gradation in the Knee region (that is, the slope is eased) In the circuit, when an image signal obtained in an imaging state (standard state) that does not need to increase the gain is input, an image with low gradation and a narrow dynamic range may be generated in an input signal range where many pixels are distributed. The problem

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