Video Sharpening is used to enhance the subjective output video quality of video processing devices. The basic sharpening approach is based on boosting the middle and high frequencies of the progressive image in the vertical and horizontal directions. The middle frequencies have to be boosted more than high frequencies to achieve a high level of perceptual quality.
The basic sharpener is in fact a FIR. For example, SD (Standard Definition) video FIR coefficients are:
-B; -A; 1+2(A+B); -A;-B
The highest subjective quality is achieved when A≈2B.
The basic video sharpener has a number of issues:
- Diagonal sharpening may be greater than vertical or horizontal
- High frequency noise is amplified
- It may cause high overshoot and undershoot of edges