JPEG-Encoder-Decoder

Encoder part

• reads raw data from a PPM image
• converts the RGB pixels to YUV pixels
• divides into 8x8 Y blocks and 4x4 U and V blocks (4:2:0 subsampling)
• performs Forward DCT (Discrete Cosine Transform) and then Quantization on an 8x8 pixels block
• performs Entropy Encoding (only ZigZag parsing and run-length encoding, NOT Huffman encoding)
• computes output entropy

Decoder part

• outputs the lists of 8x8 blocks of quatized Y/Cb/Cr coefficients
• DeQuantization phase - takes as input an 8x8 quantized block produced by the encoder and it multiplies this block (component-by-component) with the 8x8 quantization matrix
• starting from a list of 8x8 Y-values blocks and subsampled 4x4 U- and V-values blocks it composes the final PPM image