[Security Encyclopedia] Common Video Surveillance Professional Terms (3)

Ⅰ. I frame

I frame is also called intra picture. I frame is usually the first frame of each GOP that is a video compression technology used by MPEG. After moderate compression, it can be used as a reference point for random access. The I frame can be regarded as the product of an image after compression. The I frame picture is kept intact, and only the data of this frame is needed for decoding because it contains the complete picture.

Ⅱ. P frame

Forward predictive coding frame is also called predictive-frame. It is a coded image that compresses the amount of transmitted data by fully compressing the temporal redundant information of the previously coded frames in the image sequence, also called a predicted frame. P frame represents the difference between this frame and the previous key frame (or P frame). When decoding, it is necessary to superimpose the difference defined by this frame with the previously buffered picture to generate the final picture. (That is, the difference frame, P frame does not have complete picture data, only data that is different from the picture of the previous frame).

Ⅲ. B frame

It is a two-way difference frame, that is, the B frame records the difference between the current frame and the previous and next frames. In other words, to decode the B frame, not only the previous buffered picture must be obtained, but the decoded picture, through the AND of the front and rear pictures. The superposition of this frame of data obtains the final screen. B-frame compression rate is high, but the CPU will be tired when decoding.

Ⅳ. WDR

WDR refers to Wide Dynamic Range. The Wide Dynamic Range means that the particularly bright and dark parts of the scene can be seen very clearly at the same time. The wide dynamic range is the ratio of the image can distinguish the brightest brightness signal value to the darkest brightness signal value that can be distinguished.

Ⅴ. Zoom ration

It refers to the ratio of the shortest focal point to the longest focal point of a zoom lens.