The same image (an illustrated book cover) was scanned on the flatbed scanner (EPSON WF-2630) three times at 300dpi.
Analysis of the variation across the three scans:
| band | min | max | mean | std dev |
|---|---|---|---|---|
| red | 0 | 36 | 4.47 | 2.59 |
| green | 0 | 36 | 4.41 | 2.68 |
| blue | 0 | 37 | 4.72 | 2.95 |
Lossy compression could be considered acceptable if the pixel values changed due to compression are within these ranges. (That is, if the compression doesn't add any more error than what would be found by scanning the same image again.)