Digital image compression algorithms have become increasingly popular due to the need to achieve cost-effective solutions in transmitting and storing images. In order to meet various transmission and storage requirements, the compression algorithm should allow a range of compression ratios, thus providing images of different visual quality. This paper presents a modified JPEG algorithm that provides better visual quality than the Q-factor scaling method commonly used with JPEG implementations. The quantization step sizes are adapted to the activity level of the block, and the activity selection is based on an edge-driven quadtree decomposition of the image. This technique achieves higher visual quality than standard JPEG compression at the same bit rate.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Edge-adaptive JPEG image compression

We propose a new technique for transform coding based on rate-distortion (RD) optimized thresholding (i.e. discarding) of wasteful coefficients. The novelty in this proposed algorithm is that the distortion measure is made adaptive. We apply the method to the compression of mixed documents (containing text, natural images, and graphics) using JPEG for printing. Although the human visual system's response to compression artifacts varies depending on the region, JPEG applies the same coding algorithm throughout the mixed document. This paper takes advantage of perceptual classification to improve the performance of the standard JPEG implementation via adaptive thresholding, while being compatible with the baseline standard. A computationally efficient classification algorithm is presented, and the improved performance of the classified JPEG coder is verified. Tests demonstrate the method's efficiency compared to regular JPEG and to JPEG using non-adaptive thresholding. The non-stationary nature of distortion perception is true for most signal classes and the same concept can be used elsewhere.

Adaptive rate-distortion-based thresholding: application in JPEG compression of mixed images for printing

This paper presents a modified JPEG coder that is applied to the compression of mixed documents (containing text, natural images, and graphics) for printing purposes. The modified JPEG coder proposed in this paper takes advantage of the distinct perceptually significant regions in these documents to achieve higher perceptual quality than the standard JPEG coder. The region-adaptivity is performed via classified thresholding being totally compliant with the baseline standard. A computationally efficient classification algorithm is presented, and the improved performance of the classified JPEG coder is verified.

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Classified JPEG coding of mixed document images for printing

An effective method for still image compression/decompression for transmission on PSTN lines based on modifications of Huffman coding

Adaptive DCT/IDCT apparatus based on energy and method for controlling the same. The adaptive DCT/IDCT apparatus relates to a coding unit of a MPEG4/H.263 video coder, and performs an image processing operation with a high image quality at a high speed by calculating energy values for respective blocks and a mean energy value of the whole image. The apparatus includes an energy calculator for receiving an input image, dividing the input image into blocks of predetermined size, calculating energy values for respective blocks and a mean energy value, and comparing the energy values with the mean energy value; a DCT unit for dividing the input image into predetermined blocks, and performing a DCT operation on the divided blocks; an image coefficient processor for receiving DCT coefficients for respective blocks from the DCT unit according to a result of the comparison of the block's energy value and the mean energy value, and rearranging the DCT coefficients; and an IDCT unit for receiving rearranged DCT coefficients from the image coefficient processor, performing an IDCT operation on the rearranged DCT coefficients, and creating a restored image.

Adaptive DCT/IDCT apparatus based on energy and method for controlling the same

To meet various transmission and storage constraints, it is desirable that a compression algorithm allows a range of compression ratios. In this paper we analyze the JPEG compression algorithm, the international standard for compressing continuous tone images, and show how higher compression ratios can be achieved with minimal loss in image quality. We compare three methods to achieve variable compression with JPEG. Through a comprehensive analysis using 8 standard monochrome images from the USC database, we propose a method that offers substantial visual quality advantages for high compression ratios. The comparisons have been made by using an objective distortion measure which corresponds well to subjective assessments of visual quality. The paper provides detailed motivation for the algorithms, and suggests the choice of parameters to obtain variable compression with minimal loss in visual quality. >

Agrawal

Papers

Variable compression using JPEG