Region of interest coding in JPEG 2000

摘要

This paper describes the functionality in the JPEG 2000 Part 1 standard, for encoding images with predefined regions of interest (ROI) of arbitrary shape. The method described is called the Maxshift method. This method is based on scaling of the wavelet coefficients after the wavelet transformation and quantization. By sufficiently scaling the wavelet coefficients used to reconstruct the ROI, all the information pertaining to the ROI is placed before the information pertaining to the rest of the image (background), in the codestream. By varying the quantization of the image and by truncation of the codestream, different quality for the ROI and for the background can be obtained. A description is also given of how the wavelet coefficients that are used to reconstruct the ROI (ROI mask) can be found. Since the decoder uses only the number of significant bitplanes for each wavelet coefficient to determine whether it should be scaled back, an arbitrary set of wavelet coefficients can be scaled on the encoder side. This means that there is no need to encode or send the shape of the ROI. This paper also describes how this can be used to further enhance the ROI functionality. The results in this paper show that the Maxshift method can be used to greatly increase the compression efficiency by lowering the quality of the background and that it also makes it possible to receive the ROI before the background, when transmitting the image.