Image coding/compression EE5364 DSP Project Pradeep Suthram, David - PowerPoint PPT Presentation

Image coding/compression EE5364 DSP Project Pradeep Suthram, David Hemmert, Tammo Heeren All Mathcad files [MCD/PDF] can be found on: http://webpages.acs.ttu.edu/theeren

Overview l Quantization – Linear quantization – Adaptive quantization l Compression – DCT – JPEG – Wavelet

Linear Quantization l Image intensities are quantized into equidistant quantization steps [ Mathcad 2001 File] Quantization steps 255 238 221 204 187 quantized grayscale levels 170 153 136 119 102 85 68 51 34 17 0 0 17 34 51 68 85 102 119 136 153 170 187 204 221 238 255 Grayscale levels

Linear Quantization results 1 Bit 8 Bit

Linear Quantization error

Linear Quantization SNR SNR vs. grayscale resolution 60 50 40 SNR [dB] 30 20 10 0 1 2 3 4 5 6 7 8 Grayscale resolution [Bits] 6.2dB per grayscale bit

Adaptive Quantization l Quantization steps are scaled by the characteristic image probability density function [Mathcad 2001 File] Quantization steps Quantization steps 255 255 238 238 221 221 204 204 187 187 170 170 quantized grayscale levels quantized grayscale levels 153 153 136 136 119 119 102 102 85 85 68 68 51 51 34 34 17 17 0 0 0 17 34 51 68 85 102 119 136 153 170 187 204 221 238 255 0 17 34 51 68 85 102 119 136 153 170 187 204 221 238 255 Grayscale levels Grayscale levels

Adaptive Quantization results Adaptive quantization Linear quantization

Adaptive Quantization error (adaptive vs. linear)

Adaptive Quantization SNR SNR vs. grayscale resolution 60 50 40 SNR(dB] 30 20 10 0 1 2 3 4 5 6 7 8 Grayscale resolution [Bits] 5.6dB per grayscale bit for adaptive quantization [red] 6.2dB per grayscale bit for linear quantization [blue]

JPEG Algorithm 8x8 pixel DCT Level-shift Quantizer Encoder Data block • Lenna BMP file used • Gray scale image level-shifted by – 128 • for n = 8, 2^(n-1) = 128

JPEG Algorithm Quantization Encoding using a typical normalization matrix • Zig-Zag Pattern [ 16 11 10 16 24 40 51 61 • Huffman Coding 12 12 14 19 26 58 60 55 14 13 16 24 40 57 69 56 • Run-length Coding 14 17 22 29 51 87 80 62 18 22 37 56 68 109 103 77 • Tables 24 35 55 64 81 104 113 92 49 64 78 87 103 121 120 101 72 92 95 98 112 100 103 99 ] DC AC Size | Amplitude Run/Size | Amplitude

To come: l Compression – DCT – JPEG decompression – Wavelet

References: Rafael C. Gonzalez, Richard E. Wood, “ Digital Image Processing ” , Addison 1. Wesley, 1993 Geoffrey M. Davis, Aria Nosratinia, “ Wavelet-based Image Coding: An 2. Overview ” , http://www.geoffdavis.net/ Subhasis, Saha, “ Image Compression - from DCT to Wavelets : A Review ” , 3. http://www.acm.org/crossroads/xrds6-3/sahaimgcoding.html Weidong Kou, “ Digital Image Compression Algorithms and Standards, ” Kluwer 4. Academic Publishers, 1995. “ Selected Papers on Image Coding and Compression, ” Majid Rabbani, Ed., 5. Brian J. Thompson, Gen. Ed., SPIE Milestone Series, Vol MS-48, SPIE Optical Engineering Press, 1992. “ Fractal Image Compression Theory and Application, ” Yuval Fisher, Ed., 6. Springer-Verlag New York, 1995. Bernd Jaehne, “ Digital Image Processing ” , Third Edition, Springer-Verlag, 7. New York 1995