DCT (Discrete Cosine Transform)
Definition
The mathematical transformation applied to each 8x8 pixel block during JPEG compression, converting spatial pixel values into a set of frequency coefficients from low (smooth) to high (detail).
Related terms
- Blocking Artefacts
- Visible rectangular discontinuities at 8x8 block boundaries, caused by independent quantisation of adjacent blocks. At splice boundaries, misaligned block grids produce a...
- Double JPEG Compression
- The situation where an image has been JPEG-encoded, decoded to a bitmap, and then JPEG-encoded again. The second quantisation step leaves a...
- JPEG Ghost
- A visualisation technique introduced by Farid (2009) that reveals regions compressed at a quality factor different from the rest of the image....
- Quality Factor
- The 1-100 scale that most JPEG encoders expose to the user, controlling how aggressively the quantisation table rounds coefficients. The factor is...
- Quantisation Table
- A matrix of 64 integer divisors, one per DCT coefficient position, that controls how much each frequency component is rounded during JPEG...
Explained in
- JPEG Compression Artefacts and Double-Compression DetectionThe mathematical transformation applied to each 8x8 pixel block during JPEG compression, converting spatial pixel values into a set of frequency coefficients f...