HW9_JPEG_solution

HW9_JPEG_solution - Polytechnic University, Dept....

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Polytechnic University, Dept. Electrical and Computer Engineering EE3414 Multimedia Communication System I Spring 2006, Yao Wang __________________________________________________________________________________________________ Homework 9 (JPEG Image Coding) (Solution) Written Assignment : 1. Describe briefly how JPEG compresses an image. You may want to break down your discussion into three parts: a. How does JPEG compress a 8x8 image block (three steps are involved) b. How does JPEG compress a gray-scale image c. How does JPEG compress a RGB color image The basic coding unit in JPEG is a 8x8 block. For each 8x8 block, it goes through DCT, quantization, and runlength coding. Given a gray scale image, it is divided into non-overlapping 8x8 blocks. Each block is processed as above. When the input image is RGB, each color component (R, G, and B) can be compressed directly as a gray scale image. Alternatively, the RGB values of each pixel can be changed to the YcbCr values, and the Cb and Cr images can be further downsampled by a factor of 2 in both horizontal and vertical directions. Then the Y, Cb and Cr images can be coded independently, each as a gray scale image. In the interleaved mode, a minimum coding unit (MCU) consists of 4 Y blocks, 1 Cb block and 1 Cr block. The 3 components are processed simultaneously, by coding 1 MCU at a time. 2.
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This note was uploaded on 01/22/2012 for the course EE 3414 taught by Professor Wang during the Spring '06 term at NYU Poly.

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HW9_JPEG_solution - Polytechnic University, Dept....

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