We propose a direction-adaptive DWT (DA-DWT) that locally adapts the filtering directions to image content based on directional lifting. With the adaptive transform, energy compaction is improved for sharp image features. A mathematical analysis based on an anisotropic statistical image model is presented to quantify the theoretical gain achieved by adapting the filtering directions. The analysis indicates that the proposed DA-DWT is more effective than other lifting-based approaches. Experimental results report a gain of up to 2.5 dB in PSNR over the conventional DWT for typical test images. Subjectively, the reconstruction from the DA-DWT better represents the structure in the image and is visually more pleasing

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Direction-Adaptive Discrete Wavelet Transform for Image Compression

This paper proposes an efficient approach for adaptive directional wavelet transform (WT) based on directional prefiltering. Although the adaptive directional WT is able to transform an image along diagonal orientations as well as traditional horizontal and vertical directions, it sacrifices computation speed for good image coding performance. We present two efficient methods to find the best transform directions by prefiltering using 2-D filter bank or 1-D directional WT along two fixed directions. The proposed direction calculation methods achieve comparable image coding performance comparing to the conventional one with less complexity. Furthermore, transform direction data of the proposed method can be used for content-based image retrieval to increase retrieval ratio.

Adaptive Directional Wavelet Transform Based on Directional Prefiltering

Adaptive directional wavelet transform is an effective alternative of the traditional 2-D wavelet transform for image coding. It is able to transform an image adaptively along diagonal orientations as well as conventional vertical/horizontal directions. However, it requires to transmit transform direction information to the decoder side. For image coding at very low bitrates, the bit budget of the direction information degrades a reconstructed image quality. In this paper, a method to construct a scalable bitstream for transform directions is presented. We utilize the fact that the matrix yielded by transform direction indices still contains the original image characteristics. The matrix is transformed by a block-lifting based DCT, then encoded by SPIHT to yield a scalable bitstream. Our method is effective for very low bitrate image coding, and is comparable to the non-scalable one for middle-to-high bitrates.

Direction scalability of adaptive directional wavelet transform: An approach using block-lifting based DCT and SPIHT

We present a scalable registration algorithm for aligning large-frame imagery compressed with the JPEG2000 coding standard. Unlike traditional approaches, the proposed method registers the images in the compressed domain, which eliminates the need to reconstruct the full image prior to performing registration. Two forms of scalability are exploited during registration: resolution and quality. Resolution scalability results from the native multiresolution image representation of the discrete wavelet transform utilized as a building block in JPEG2000. Quality scalability relates to the embedded block coding with optimal truncation (EBCOT) used for compressing the wavelet coefficients. This combination allows registration on selectable resolution levels and quality layers, which enables registration of large-frame imagery at low bit rates over constrained bandwidth channels. Furthermore, the hierarchical nature of the algorithm provides a trade-off between registration accuracy and computational complexity. Experimental results show that the proposed algorithm exhibits consistent registration performance across a range of quality levels (3.5 to 0.5 bpp) for frames sizes of 2 K×4 K. We present simulation results with imagery collected from a prototype persistent surveillance system to demonstrate the feasibility of the proposed algorithm in real-world scenarios.

Scalable image registration with JPEG2000

The direction-adaptive discrete wavelet transform (DA-DWT) locally adapts the filtering direction to the geometric
flow in the image. DA-DWT image coders have been shown to achieve a rate-distortion performance superior
to non-adaptive wavelet coders. However, since the direction information must always be signalled regardless of
total bit-rate, performance at very low bit-rates might be worse. In this paper, we propose two scalable direction
representations: the layered scheme which is similar to the scalable motion vector representation in scalable
video coding and the level-unit scheme which provides finer granularity upon the layered scheme. Experimental
results indicate that we can achieve the desirable performance at both low and high bit rates with our proposed
level-unit scheme. Significant improvement in image quality (about 3-5 dB) is observed at very low bit rate,
relative to non-scalable coding of the direction information.

/pdf/scalable-direction-representation-for-image-compression-with-3ubnni3gup.pdf

Scalable direction representation for image compression with direction-adaptive discrete wavelet transform

The direction-adaptive discrete wavelet transform (DA-DWT) locally adapts the filtering direction to the geometric flow in the image. DA-DWT image coders have been shown to achieve a rate-distortion performance superior to non-adaptive wavelet coders. However, since the direction information must always be signalled regardless of total bit-rate, performance at very low bit-rates might be worse. In this paper, we propose two scalable direction representations: the layered scheme which is similar to the scalable motion vector representation in scalable video coding and the level-unit scheme which provides finer granularity upon the layered scheme. Experimental results indicate that we can achieve the desirable performance at both low and high bit rates with our proposed level-unit scheme. Significant improvement in image quality (about 3-5 dB) is observed at very low bit rate, relative to non-scalable coding of the direction information.

Tao Xu

Papers

Scalable direction representation for image compression with direction-adaptive discrete wavelet transform

Scalable direction representation for image compression with direction-adaptive discrete wavelet transform