This filter is found in Image>Filters/Enhance/Deinterlace

Images captured by videocards, especially when fast movement is recorded, may look blurred and stripped, with splitted objects. This is due to how cameras work. They don't record 25 images per second, but 50, with half vertical resolution. There are two interlaced images in one frame. First line of first image is followed by first line of second image followed by second line of first image... etc. So, if there have been an important move between the two images, objects will appear splitted, shifted, stripped.

The Deinterlace filter keeps only one of both images and replaces missing lines by a gradient between previous and following lines. The resulting image, or selection, will be somewhat blurred, but can be improved by enhance filters

A test image can be found at www.alparysoft.com