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These blocks can then be subjected to discrete cosine transform (DCT) to calculate the frequency components, both horizontally and vertically. [1] The resulting block (the same size as the original block) is then pre-multiplied by the quantization scale code and divided element-wise by the quantization matrix, and rounding each resultant element.
Image compression is a type of data compression applied to digital images, to reduce their cost for storage or transmission. Algorithms may take advantage of visual perception and the statistical properties of image data to provide superior results compared with generic data compression methods which are used for other digital data.
The macroblock is a processing unit in image and video compression formats based on linear block transforms, typically the discrete cosine transform (DCT). A macroblock typically consists of 16×16 samples, and is further subdivided into transform blocks, and may be further subdivided into prediction blocks.
The DCT-II is an important image compression technique. It is used in image compression standards such as JPEG, and video compression standards such as H.26x, MJPEG, MPEG, DV, Theora and Daala. There, the two-dimensional DCT-II of blocks are computed and the results are quantized and entropy coded.
The most common form of lossy compression is a transform coding method, the discrete cosine transform (DCT), [2] which was first published by Nasir Ahmed, T. Natarajan and K. R. Rao in 1974. [3] DCT is the most widely used form of lossy compression, for popular image compression formats (such as JPEG ), [ 4 ] video coding standards (such as ...
Block Truncation Coding (BTC) is a type of lossy image compression technique for greyscale images. It divides the original images into blocks and then uses a quantizer to reduce the number of grey levels in each block whilst maintaining the same mean and standard deviation.
The discrete cosine transform (DCT) image compression algorithm has been widely implemented in DSP chips, with many companies developing DSP chips based on DCT technology. DCTs are widely used for encoding , decoding, video coding , audio coding , multiplexing , control signals, signaling , analog-to-digital conversion , formatting luminance ...
The techniques MozJPEG uses to achieve high compression include optimising Huffman trees, using progressive coding to optimally split the spectrum of DCT coefficients into separate scans, and through the use of trellis quantisation. Additionally, the presets are aggressively tuned towards the minimisation of file sizes.