Graduation improvement circuit null of electronic still

摘要

PURPOSE:To obtain excellent picture quality while suppressing the effect of quantization noise even for an object with a low illuminance in a digital electronic still camera. CONSTITUTION:An analog luminance signal 19 is inputted to an A/D converter 15, in which the signal is converted into an 8-bit digital luminance signal based on an upper limit reference voltage 41 and a lower limit reference voltage 42. The signal is written in a video memory 22 by using a memory control circuit 18. A maximum value detection circuit 28 detects a maximum value of the digital luminance signal by one frame in the video memory 22 and transfers it to a CPU 31. When the maximum value is a prescribed value or below, the CPU 31 revises the digital data given to a D/A converter 39 via a latch circuit 36 thereby revising the upper limit reference voltage 41 to a small value. Thus, A/D conversion with a high gain is implemented for an object with a low illuminance and the result is recorded in a memory card 24. The amplification factor is corrected at the reproduction as to the picture data subjected to A/D conversion by revising the upper limit reference voltage.