Quantitative Analysis of Image Quality of Lossy Compression Images

High resolution images acquired by an aerial digital camera and high resolution satellite images are expected to become more powerful data source of GIS. Since the large data volume of a high resolution image brings difficulties in dealing with it, lossy image compression is going to be indispensable. Image quality of a reconstructed image after decompression is usually evaluated by visual inspection. Although some numerical measures such as RMSE or PSNR are used to compare various image compression techniques, numerical evaluation of quality of a reconstructed image is seldom conducted. Therefore, we decided to carry out an empirical investigation into the effects of lossy image compression on quality of color aerial images by using color and texture measures. From the experiment results, it can be concluded that color space conversion and downsampling in JPEG compression have an effect on quality of a reconstructed image. The results supported that lossy JPEG 2000 compression is superior to lossy JPEG compression in color features. However, lossy JPEG 2000 compression does not necessarily provide an image of good quality in texture features. Moreover, the results indicated that an image of finer texture features is less compressible, and quality of the reconstructed image is worse in both color and texture features. Finally, it was confirmed that it is difficult to set an appropriate the quality factor, because the optimal setting of the quality factor varies from one image to another.