An electronic endoscope system includes a video scope having a solid-state image sensor for successively producing a frame of color image-pixel signals, and an image-signal processor for producing a color video signal based on the frame of color image-pixel signals. A calculation system calculates a difference value between a value of a central single-color image-pixel signal and an average of values of one selected from single-color image-pixel signals surrounding the central single-color image-pixel signal. A color-balance alteration system alters the value of the central single-color image-pixel signal based on the difference value calculated by the calculation system. A selection system performs the selection of the circumferential image-pixel signals such that the circumferential image-pixel signals to be selected are farther from the central image-pixel signal, as a spatial frequency of an endoscope image to be reproduced based on the color video signals is lower.