Q9Computer Graphics and Multimedia
Question
Define JPEG compression.
Answer
JPEG compression is a lossy image compression standard that uses DCT and quantization to reduce image file size significantly.
JPEG (Joint Photographic Experts Group) compression is a standardized lossy image compression method designed for photographic images with continuous tonal variation. The compression pipeline: (1) Convert RGB → YCbCr, (2) Optional chrominance downsampling (4:2:0), (3) Divide image into 8×8 pixel blocks, (4) Apply Discrete Cosine Transform (DCT) to each block, (5) Quantize DCT coefficients using a quantization table (this is the lossy step — higher quantization = more loss), (6) Entropy code using Huffman or arithmetic coding.
JPEG achieves compression ratios of 10:1 to 20:1 with little perceptible quality loss. The quality factor (1–100) controls the trade-off between file size and image quality. JPEG is ideal for photographs but introduces blocking artifacts at very high compression ratios. The newer JPEG2000 uses wavelet transforms instead of DCT for better quality.