实现感兴趣区域编码的通用部分位平面偏移法

New Region-of-Interest Image Coding Method:Generalized Partial Bitplanes Shift

提出一种通用的部分位平面偏移方法(GPBShift),可克服JPEG2000中定义的两种标准感兴趣区域(ROI)编码方法的局限性。与标准方法中将全部位平面用统一的偏移值进行移位不同,该方法将ROI系数和背景(BG)系数的位平面分别划分成两部分,进行不同的位平面偏移,以控制ROI和BG区的相对重要性。GPBShift方法兼容Maxshift、GBbBShift和PSBShift3种方法,并提供比上述3法更大的灵活性。它不仅能够在不传输任何形状信息的情况下,对任意形状的ROI进行编码,而且通过选择偏移值,能灵活调整ROI和BG区的相对压缩质量。此外,它能够根据不同的优先级,编码多个ROI区域。实验结果显示:该方法在低码率时,能提供比Maxshift方法更好的视觉质量,且比标准中的一般偏移方法(generalscalingbasedmethod)具有更高的编码效率。

Region-of-interest (ROI) image coding is a new feature in JPEG 2000, which allows for encoding the ROI in an image with better quality than the background (BG). Considering the limitations of two standard ROI coding methods defined in JPEG 2000, a new improved ROI coding method called generalized partial bitplanes shift (GPBShift) is presented. To control the relative importance between ROI and BG, the method divides the bitplanes of ROI and BG coefficients into two parts by using two scaling values respectively. Instead of shifting the bitplanes all at one by the same scaling value in the standard methods, GPBShift shifts part of them on the basis of the bitplane shifting scheme. The Maxshift,generalized bitplane-by-bitplane shift (GBbBShift) and partial significant bitplanes shift (PSBShift) methods are special cases of the GPBShift method, while GPBShift provides more flexibility for degree-of-interest adjustment of the ROI. The GPBShift method can code arbitrarily shaped ROI without explicitly transmitting any shape information to the decoder, and flexibly select the scaling values to adjust relative compression quality in ROI and BG. Additionally, the method can efficiently code multiple ROI with different priorities in an image. Experiments show that it can provide significantly better visual quality than the Maxshift method at low bit rates, and higher coding efficiency than the general scaling based method.