A sharpness filter processes a video signal that is to be displayed in a windowed environment. The windowed environment may contain windows that for displaying television images derived from video standards such as NTSC, PAL, and SECAM. Displaying windowed television images results in line scan rates and spatial frequencies that differ from the line scan rate and spatial frequency specified by the original video standard. The sharpness filter of the invention emphasizes certain high frequency components of the video signal in accordance with the encountered spatial frequencies. A control circuit for the sharpness filter provides a linear correlation between a user control and the center frequency of the sharpness filter. The sharpness filter shapes the output signal to avoid saturation and overdriving of video input amplifiers. The circuit can be implemented using a low-cost CMOS process.