The discrete cosine transform (DCT) is a method for converting time-related signals into frequency-related ones. The difference to the Fourier transform is that in the DCT transform the conversion takes place in two dimensions, whereby not all frequencies
, aretreated differently than higher frequencies, which represent a rapid change in brightness and thus resolution
andcontour. The distinction between lower and higher frequencies is important because it can affect image sharpness.
In termsof procedure, the DCT transform breaks up the frames into 8x8 blocks
.vector of 64 pixel values containing the brightness and color values, where each block also represents a specific frequency range
. The brightness and color blocks are treated separately.
of the 8x8 block. The other values in the horizontal represent the brightness changes, starting with small changes and increasing to the shortest changes. So that the second value (2) in the horizontal is a measure of the brightness progression from left to right. The third (3) indicates whether the brightness changes to the center and then back to the edge; thus, the value reflects a bifurcated axis. Thesame criteria are applied vertically, but for the vertical axis of the image.
This data is used to create a coefficient matrix, the data of which is compressed using quantization in JPEG. The DCT transformation itself does not cause any data compression. The disadvantage is that images encoded with DCT no longer correspond to the original signal after decoding.