Coefficient Scanning and Segmentation Techniques for Shape Adaptive Image Compression
Date Issued
2010
Date
2010
Author(s)
Lin, Pao-Yen
Abstract
Nowadays, coding of arbitrarily shaped image region is becoming an important feature in many visual coding applications. The advantage of shape-adaptive coding is that it can employ the information of arbitrarily-shaped region to exploit the high correlation of the color values within the same image segment in order to achieve a higher compression ratio. Compared to the conventional block-based image coding, shape-adaptive image coding produces significantly less blocking artifacts and distortions in other forms which typically emerges in block-based image coding since its negligence of the image content and characteristics.
Traditionally, shape adaptive image coding relies on the Gram-Schmidt process the obtain orthonormal bases for an arbitrarily-shaped image segment. However, this method causes severe complexity issue. On the contrary, other methods may take low computation complexity but are not efficient in shape adaptive image coding.
In this thesis, a new approach of object coding based on the two dimensional orthogonal DCT expansion in triangular and trapezoid regions is proposed. In general, any image segment can be viewed as a polygon and a polygon can be decomposed into several triangular or trapezoid regions. In this thesis, we propose a triangular and trapezoid segmentation algorithm to achieve the trapezoid approximation of an image segment.
Besides, like the other shape adaptive transformations, applying the 2-D DCT expansion on these trapezoid regions leads up to irregular-shaped coefficient block. However, the existed zigzag scanning order does not concern the shape of the coefficient block. Solutions of scanning these irregular-shaped coefficients according to its shape are proposed on this thesis. The proposed coefficient scanning scheme can easily be implemented in existing image compression scheme.
Results show that the trapezoid approximation of any image segments can be found and it nearly matches the shape of the image segments. Moreover, the proposed coefficient scanning scheme for generalized shaped can improve the coding efficiency. Finally, the proposed image compression scheme achieves better performance than the conventional JPEG image compression standard.
Index terms— JPEG, Shape adaptive transform, coefficient scanning, image segmentation.
Subjects
MPEG
JPEG
Image compression
Shape adaptive
Coefficient scanning
Image segmentation
object-based video coding
Type
thesis
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