CompuServe Messages

Thanks for the information – using data from a single vertical scan seems to be the only way to get sharp images of moving subjects. Being used to movie film, I find the "still" frames from a video monitor pretty strange. If you have a vertical line moving fairly quickly from left to right in the scene, a movie camera gives you a series of images with straight vertical lines at successive positions. Each one of them is an accurate "still" of the original subject. In video, the first scan produces an "almost vertical" column of pixels on alternate scan lines, with the bottom pixel displaced to the right by the amount the vertical line has moved in 1/60 second. The second scan, which is supposed to fill in the spaces between the first column of pixels, starts directly above the last pixel in the first column and does the same thing. So, instead of a straight vertical line, you end up with two slanted dotted lines. We don't notice this if the image keeps moving as it's supposed to, but it isn't a very satisfactory "still" of the original. "Grabbing" a single vertical scan may not give you broadcast quality, but at least it gives you sharper images!