Deinterlacing the process of converting interlaced images of video into non-interlaced form.

Interlaced video draws only half of the lines on the screen for each frame (alternately drawing the odd and even lines for each frame), taking advantage of the time it takes for a image to fade on a CRT to give the impression of double the actual refresh rate, helping to prevent flicker.

When displaying video on a display that can support a high enough refresh rate that flicker isn't perceivable, interlaced video can be deinterlaced for better viewing. When a display cannot interlace but must draw the entire screen each time, the video must be deinterlaced before it can be displayed.

Deinterlacing Methods

There are various methods to deinterlace video, each producing different artifacts. Artifacts will always be present in deinterlaced video, as the process must deal with the fact that interlaced video has only half the information of non-interlaced video.

There are two basic methods of deinterlacing: combination, where the even and odd frames are combined into one image and then displayed, and extension, where each frame (with only half the lines) is extended to the entire screen.

Frame Combination Deinterlacing

• Weaving is when the even and odd frames are simply added together. This is fine when the image hasn't changed between frames, but any change will result in artifacts known as "mouse teeth", when the pixels in one frame do not line up with the pixels in the other, forming a jagged edge. This technique retains full vertical resolution.

• Blending is when an odd and even frame are blended, or averaged together and displayed as one frame. The mouse teeth are blurred out, resulting in a ghosting effect. The image loses vertical resolution and thus looks a little softer.

• Selective blending , or smart blending, is a combination of weaving and blending. As areas that haven't changed from frame to frame don't need any processing, the frames are weaved and only the areas that need it are blended.

Frame Extension Deinterlacing

• Half-sizing displays each interlaced frame on its own, resulting in a video with half the vertical resolution of the original, unscaled. Understandably, this is never used for regular viewing.

• Line doubling takes the lines of each interlaced frames (consisting of only even or odd lines) and doubles them, filling the entire frame. This results in the video having effectively half the vertical resolution, scaled to the full resolution. While this prevents mouse teeth, it causes a noticeable reduction in picture quality. This technique is also called bob deinterlacing, because small details appear to bob up and down as a result.