We propose a new method for JPEG2000 region of interest (ROI) coding called the background pretruncated method (BPTM). An algorithm to calculate the key parameter in the BPTM is also proposed. The published JPEG2000 ROI coding methods have difficulty in balancing ROI quality and system computation. Methods based on shifting coefficients add much computation, and they significantly penalize the coding efficiency. Implicit methods cannot obtain as high-ROI quality as the coefficient shift methods. To efficiently achieve ROI coding, the BPTM assigns a proper number of the least significant bitplanes of the background to zero, and it can not only achieve high-ROI quality but also add no computation to the other modules in JPEG2000. Additionally, the BPTM supports arbitrary shaped ROI coding, and the codestream is compatible with JPEG2000 standard.