Video compression, how it works
Video – This is essentially a three dimensional pixel color matrix. Two measurements indicate the vertical and horizontal resolution of the frame, and the third dimension, this time. Frame – is an array of pixels, visible camera at this moment of time, or just an image. Video is also possible so-called half images (see: Interlace Scan System).
Compression might be impossible, if I would each frame was unique and the pixel placement was completely random, but it’s not so. Therefore, you can compress, in – first, the image itself – for example, the sky blue photo without sun will actually be reduced to the outline dotted description and a gradient fill. In – Second, you can compress a similar neighboring frames. Ultimately, the algorithms for image and video compression are similar, if you consider video as a three-dimensional image with time as the third coordinate.
Lossless compression
In addition to lossy video compression, it can also be compressed and lossless. This means that when the decompression result will be a precision (bit bits) that matches the original’s. However, when lossless compression is impossible to achieve high compression ratios in real (not artificial) video. For this reason, almost all commonly used videos are lossy compressed (by that number on consumer digital video discs, video sharing, on satellite broadcast). On the web – sites for small clips without sound sometimes use simple GIF and APNG formats.
Compress technology and video compensation motion
One of the most powerful technologies, which allows to increase the degree of compression, this compensation movement. When any modern video compression system later frames in the sequence uses the similarity of regions in the previous frames to increase the degree of compression. However, since – for any traffic – any objects in the frame (or the camera itself), the use of adjacent frame similarity was incomplete. Motion compensation technology allows you to find similar sites, even if they move from the previous frame.
The current state of affairs
РЕКЛАМА
Cm. See also: HTML5 video
At the end of 2011 the year almost all algorithms compress the video (for example, the standards, adopted by the ITU – T and ISO) using a discrete cosine transform (DCT) or its modification to eliminate spatial redundancy. Other methods, such as a fractal compression and discrete wavelet- transform, have also been the subject of investigation, but are now generally used only for compression of still images.
The use of most compression methods (such as the discrete cosine transform and wavelet – conversion) also involves the use of the quantization process. Quantization can be like scalar, so and vector, so there are less, most compression schemes in practice use scalar quantization for its simplicity.
Television
Modern digital television broadcasting is available precisely thanks to video compression. The television station can transmit not only high definition video (HDTV), but also it and several channels on one physical channel (6 MHz).
Although most of today’s video content is broadcast with the use of the MPEG – 2 video compression standard, the no less new and more efficient standards for video compression already used in broadcasting – for example, H . 264 and VC – 1.
