The first image depicted in FIGS. 1A-1B includes only a small amount of image data (e.g., roughly 20-45% of the image data, depending on the image). This image data might include, for instance, all but the last two bits for the DC coefficients for all three image channels (Y, Cr, and Cb). At full size (FIG. 1A), this image is clearly of quite low quality. However, when reduced in size (FIG. 1B), the quality may be sufficient for the image to serve as a reasonable thumbnail.
The second image depicted in FIG. 1C includes additional data that supplements the data making up the thumbnail from FIG. 1A (e.g., roughly 36-67% of the image data, depending on the image). The low-quality image data might include data from several scans; in one example, this might include the remaining bits from the DC coefficients for all three image channels, as well as other data (e.g., the AC coefficients for both chroma channels and all but the last two bits of the AC coefficients from the luma channel). This image may be suitable for use as a low-quality image. The resulting image is of higher quality than the thumbnail, but the difference between this low-quality image and the full-quality image may be readily apparent.
