Ikuro Ueno

Embedded block coding in JPEG2000

This paper describes the embedded block coding algorithm at the heart of the JPEG2000 image compression standard. The algorithm achieves excellent compression performance, usually somewhat higher than that of SPIHT with arithmetic coding, but in some cases substantially higher. The algorithm utilizes the same low complexity binary arithmetic coding engine as JBIG2. Together with careful design of the bit-plane coding primitives, this enables comparable execution speed to that observed with the simpler variant of SPIHT without arithmetic coding. The coder offers additional advantages including memory locality, spatial random access and ease of geometric manipulation.

Region-of-interest coding in volumetric images with shape-adaptive wavelet transform

We evaluated some arbitrary-shape ROI (Region of Interest) coding techniques for three-dimensional volumetric images, and through the observation we propose a flexible ROI coding with efficient compression performance. In arbitrary-shape ROI coding, the object in an image is coded with higher fidelity than the rest of the image, together with the shape information, which indicates the region of the object. In our proposed method (named as SA-ROI), in which shape-adaptive wavelet transform and scaling-based ROI coding are incorporated, the samples within the object are transformed with three-dimensional shape-adaptive wavelet transform according to its shape-information. If necessary, the background is also transformed by shape-adaptive wavelet transform independently. Then the samples within the object are scaled up by a certain number of bit-shifts, and encoded from the MSB (Most Significant Bit) plane by plane so that coefficients within the object are encoded earlier and have higher fidelity than the background. Compared with the scaling-based ROI coding using ordinary wavelet transform, which has almost the same ROI coding functionalities, SA-ROI outperforms by 5% in lossless compression ratio. Also in lossy coding, except at very low coding rates, SA-ROI has better compression performance.

Efficient coding of computer generated images with acceptable picture quality

Coding of computer generated (CG) images with visually acceptable quality is studied based on the lossless/near-lossless coding methods defined in the JPEG-LS standard, including their modification. First, a color transform into YCbCr is done and its lossless coding is found to reduce the lossless coding in RGB space by 20-53%. As the normal JPEG-LS near-lossless coding methods are found not to provide acceptable image quality, another compatible method to JPEG-LS is proposed and found to reduce the bit-rate of lossless coding by about 20-30%, while keeping almost acceptable picture quality. Finally, we propose a new method that can achieve a reduction of bit-rate from YCbCr lossless coding by 22-44%, keeping acceptable image quality for both. natural and CG images, though not compatible to JPEG-LS.