DCT coefficient histogram
Definition
A histogram of the discrete cosine transform coefficients across macroblocks or coding units in a frame or clip. After a single encode, the histogram has a characteristic shape with peaks at quantisation multiples. After re-encoding, additional peaks or gaps appear that reflect the quantisation grid of the first generation.
Related terms
- Double compression
- The condition in which a video has been encoded at least twice through a lossy codec. The term is also used loosely...
- Group of Pictures (GOP)
- The periodic structure of I-frames, P-frames, and B-frames in a compressed video stream. Each encoding generation imposes its own GOP structure. When...
- Intra-refresh artefact
- The elevated count of intra-coded macroblocks or CTUs at frame positions that correspond to the I-frame interval of a previous encoding generation....
- Macroblock (MB) / Coding Tree Unit (CTU)
- The basic spatial coding unit: 16x16 pixels in H.264 (macroblock) and up to 64x64 pixels in H.265 (CTU). Each unit is classified...
- Quantisation parameter (QP)
- A per-block or per-slice value that controls the coarseness of the DCT coefficient rounding step in H.264 and H.265. Higher QP means...
Explained in
- Compression History Estimation in Video StreamsA histogram of the discrete cosine transform coefficients across macroblocks or coding units in a frame or clip. After a single encode, the histogram has a cha...