WATCH THE COMPRESSION TEST

Coloring Page Maker: JPEG Input Compression Test

Three matched inputs, one unchanged tracing function. This video explains the measurements and their limits.

Read the full experiment · Download video

Transcript

Can JPEG compression add extra lines in a coloring page maker? It can change the traced edges. Start with the original file. Saving a compressed JPEG as PNG does not restore information already lost.

We drew one 600 by 400 image and saved it as PNG, JPEG quality 90, and JPEG quality 10 using Pillow. We decoded the three files and passed them through this site's unchanged Detailed tracing function. The tool interface and export stages were not tested.

The PNG trace contained 3968 pixels below gray 128. The quality 90 JPEG contained 2942. The quality 10 JPEG contained 3619. Dark-pixel counts are not accuracy scores. We also measured marks at locations that were white in the PNG trace. Some are shifted contours, so we do not call every changed pixel an artifact.

Keep the original and compare the same crop and style. If you only have a small compressed copy, request the original when possible. PNG prevents another lossy save, but cannot reconstruct lost details. Read the exact files, measurement method, and limitations in the guide.