In this paper

an improved JPEG-LS algorithm is proposed to meet the needs of higher near-lossless compression ratio for remote sensing images. First

the threshold magnitude for run-length coding is increased and a prediction based on the control of local gradient is employed to extend the average run-length value

and this results in higher compression ratio. Second

because the subjective quality of the reconstructed image compressed by JPEG-LS at higher ratio degrades quickly

an error-modifying approach is added to the run-length coding area and a smoothing filter is applied to the reconstructed image. Thus the rebuilt image when observed by human eyes is much better and the objective quality measured byPSNRis higher as well. Finally

Golomb-Rice Coding method

which is a part of the original JPEG-LS

is adopted to encode residual errors. This can control the maximum absolute error of every pixel value in the rebuilt image and therefore keeps the great advantage of the original JPEG-LS in the sense of error control style. Integrating the above measures into a software package

under the same limit of ±7 for maximum absolute error of every pixel value

not only the compression ratio is somewhat increased

but also the human visual perception is obviously improved in the comparison with JPEG-LS. In our experiments

PSNRis about 1～3dB higher.