Introduce The Image Format Of The Video Capture Card

Introduce the image format of the video capture card

The image data of the video capture card can be compressed because there is more or less redundant information in the data, and for multimedia information such as video and audio, the redundancy of human beings can be utilized to achieve a higher compression ratio. The image formats of common video capture cards are generally CIF format and D1 format.

The following three dimensions of the three main performance indicators for measuring compression algorithms are as follows:

Compression ratio

Compression quality (distortion)

Compression and decompression efficiency

According to whether the decoded data is completely consistent with the original data, the data compression method is divided into two categories:

(1) Reversible coding (no distortion coding, lossless compression)

Such as HUF editing, arithmetic coding, run length coding, etc.

(2) Irreversible coding (with distortion, lossy compression)

Transform coding and predictive coding

The video capture card data compression method can be classified as follows according to the principle:

1. Information entropy coding (statistical coding)

2, predictive coding

3, transform coding

4, model coding

5, mixed coding

Video capture card For video coding applications, before encoding compression and transmission, you first need to convert the video image to an intermediate format (CIF format), a common intermediate grid.

The format corresponds to a common set of frame resolutions, such as CIF format with a resolution of 352*288 pixels and 4CIF resolution of 704*576 pixels. For CIF images, before uncompressed,

The number of bits required for one frame of image is as follows, assuming an 8-bit sampling depth

If using: 4:2:0 format, 352*288*12=1216512=1. 2MBIT

If adopted: 4:4:4 format, 352*288*24=2433024=2. 4MBIT

Then, if the real-time 25 frames/sec stream setting is used, the code stream needs to reach 30 MBPS in the former format, and the space required for one hour of recording is 108G. code

Stream and space requirements are unacceptable in practical applications. This is the necessity of video compression. Common image format PAL

CIF352*288

D1704*288

D1704*576

This is the result, basically the current compression technology, the image format commonly used in video capture cards, can achieve three compression formats in the PAL case, that is, the city

No matter what kind of video capture card on the field, only one of these three image formats can be realized. Most of the soft press cards can only achieve the first two, but only a few hard press cards.

The last one can be achieved, that is, image acquisition and image viewing in the D1 format.