What is the difference between interlaced and progressive scan of video conference cameras

Interlaced and Progressive are both methods of expressing moving images on the display device. The interlaced method is that each frame is divided into two fields and displayed alternately. The progressive method is to display all the images in each frame. Simultaneous display. The usual scanning method of LCD TV displays is from left to right and top to bottom, scanning a fixed number of frames per second.


Interlaced scanning means that each frame is divided into two fields. Each field contains all the odd or even scan lines in a frame. Usually, the odd lines are scanned first to get the first field, and then the even lines are scanned to get the second field. Due to the persistence of vision effect, the human eye will see smooth motion instead of flickering half-frame images. But at this time, there will be flickers that are hardly noticed, which makes the eyes tired. When the content of the screen is horizontal stripes, this flicker is particularly easy to notice.
Progressive scan displays the entire scan frame every time. If the frame rate of progressive scan is the same as the field rate of interlaced scan, the human eye will see a smoother image than interlaced scan, and the flicker is smaller than interlaced scan. The progressive scanning method makes the frequency spectrum of the signal and the channel bandwidth for transmitting the signal reach high requirements. The operating principle is to divide a 625-line image into two fields to scan. The first field is called the odd field, and only the odd lines of 625 lines are scanned (scanning 1, 3, 5, … lines in turn), and the second field (even field ) Only scan the even-numbered lines of 625 lines (scanning 2, 4, 6, … lines in sequence), and complete the number of lines scanned by the original frame of image through two-field scanning, which is interlaced scanning. For the interlaced scanning with 625 lines per frame, each frame is scanned in two fields, each field only scans 312.5 lines, and only 25 frames of images per second are scanned, so a total of 50 fields per second are scanned ( The odd field and the even field each have 25 fields), that is, the frame frequency is 25 Hz and the field frequency is 50 Hz during interlaced scanning.

Post time: Oct-12-2020