PJ Jacobowitz issues the following image quality verdict in the review of the Canon SD970 IS / IXUS 990 IS:
In the center of the frame—typically the highest-quality section of an image—the SD970 captured an impressive 2397 lines per picture height. As you move to the image's outer edges, that number drops by an average of 33 percent, which is considerable, but still acceptable. By comparison, the Sony Cyber-shot DSC-T90 averaged 2274 lines in the center of images, but dropped by just 18 percent at the outer edges.
The SD970 does an excellent job at suppressing noise at high ISO sensitivities (which is great for shots taken in poorly lit conditions). The SD970 kept noise below noticeable levels from ISO 80 to 400, with excellent results even up at ISO 800 and 1600.