Image Compression by Segmentation and Boundary Description
Date Issued
2008
Date
2008
Author(s)
Huang, Jiun-De
Abstract
The present technique of image compression, like the JPEG standard, makes the same process to whole image and does not adjust the parameters based on the local characteristics of the image. Therefore, it has a limit to its compression ratio. However, a new compression technique called segmentation-based image compression has been developed. It segments an image to several regions with similar characteristic or color. Because each image segment has different shapes and color values, we compress these regions individually. Due to the high correlation of the color values in an image segment, we could achieve higher compression ratio in theory.The technique of image segmentation is based on two properties of color values: discontinuity and similarity. To find the discontinuity of the color values, we will intro-duce the image edge detection technique and propose an adaptive method called the short response Hilbert transform (SRHLT) which combines the traditional differential method and the Hilbert transform method. We will also discuss many other ways to segment an image. The main object is to find a suitable segmented result that can be compressed efficiency.After Segmentation, we will introduce the basic image compression algorithms in JPEG standard and apply them in our proposed methods. To record the boundary of an image segment efficiently, we will introduce some popular boundary descriptors and propose two improved boundary descriptors. To compress the color values of an image segment, we will discuss how to transform an arbitrary-shape image segment to fre-quency domain. Then we can quantize and encode the frequency coefficients to de-crease the information quantity. Finally, we will compare the result with that of JPEG standard and prove that the compression ratio could be increase a lot under acceptable distortion.
Subjects
Edge detection
Image segmenation
Image compression
Fourier description
Arbitrary-shape DCT
Type
thesis
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