Patent US 5,081,692

A pseudo center weighted local variance in the neighborhood of an image pixel determines the amplification factor multiplying the difference between the image pixel and its blurred counterpart before it is combined with the original image. The amplification factor is computed for each pixel in the image, and varies from a minimum value of about -1 when the center weighted variance is at a minimum value to some maximum value when the center weighted variance reaches a maximum value. The pseudo center weighted variance is computed by convolving the local neighborhood surrounding each image pixel with a kernel of center weights having a maximum value at the center pixel. The pseudo center weighted variance is the difference between the center weighted mean of the source of the local neighborhood of image pixels and the square of the center weighted mean. Both image sharpening and noise suppression is achieved in the same image by permitting the amplification factor to vary between a fraction of unity and greater than unity as the center weighted variance varies from a low value (uniform image) to a higher value (textured image).