Digital signal and image processing
Wait, what?
Every JPEG is secretly a sum of cosine waves
Your photos are not made of pixels
Quick check · tap an answer to continue
Lesson notes
Key points
- JPEG cuts the image into 8 by 8 pixel blocks and rewrites each block using the discrete cosine transform.
- Your eye barely notices fine stripes, so JPEG stores the strong smooth patterns and throws most fine ones away.
Definitions
- Discrete Cosine Transform
- Rewrites a block of pixels as weighted sums of 64 cosine patterns, from smooth to finely striped.
Takeaway: JPEG stores cosine weights per 8×8 block, then drops fine detail.
Quick check: What size blocks does JPEG split an image into?
- 4×4 pixels
- 8×8 pixels
- 64×64 pixels
Standard JPEG applies the DCT to 8×8 pixel blocks.
DCTQuantisation
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