1. A signal correcting method, comprising: obtaining image data containing at least a first hue signal and a second hue signal in correspondence to each pixel; and substituting a signal value of the first hue signal at a target pixel with an average of the signal value of the first hue signal at the target pixel and a signal value of the first hue signal at a nearby pixel, and a signal value of the second hue signal at the target pixel with an average of the signal value of the second hue signal at the target pixel and a signal value of the second hue signal at the nearby pixel, when the signal value of the first hue signal at the target pixel and the signal value of the first hue signal at the nearby pixel are determined to be symmetrical to each other relative to a signal value of the first hue signal corresponding to a specific color and the signal value of the second hue signal at the target pixel and the signal value of the second hue signal at the nearby pixel are determined to be symmetrical to each other relative to a signal value of the second hue signal corresponding to the specific color.