I forgot to say that changing the resolution didn't change much. When the scanner lowers the resolution, it also reduces the optical resolution (lower the spatial cutoff frequency) to avoid aliasing problem.(posted 8096 days ago)I realized that those JPEG files don't look as nearly good as other JPEGs of similar file sizes. I think the mottled tones act as "details" to be preserved by the compression algorithm and they inflate the file size!!