Sharpen a JPG: what changes with quality
| Estimated quality | Deblock and dering | Save quality |
|---|---|---|
| 80 and above | Off | Same as the source |
| 70–79 | On | Same as the source |
| under 70 | On, with a higher sharpen threshold | Same as the source |
Related on this site
- For a lossless PNG, screenshot or logo: sharpen a PNG.
- If the JPG is about to be resized for the web: sharpen after resizing.
- For any other picture: the sharpener.
Questions: sharpen a jpg
Why does sharpening a JPG make the blocks show?
A JPEG is stored in 8 × 8 blocks, and at lower quality the edges between blocks and the ripples beside strong edges are already there, just faint. A sharpen steepens every edge it finds, including those. This page calms them first — only where the picture is flat, only on the file's own 8 × 8 grid — and then sharpens.
How does it know the quality my JPG was saved at?
It reads the quantisation tables in the file's header and compares them with the standard tables, which gives the IJG-scale quality the encoder used. No decoder or upload is involved; the tables are a few hundred bytes near the start of the file.
Why does the save default to that quality?
Because re-encoding a quality-60 file at 92 nearly doubles its size without bringing back anything the first encode removed. Matching the source keeps the file in proportion; you can change it before saving.
Will the file get bigger?
Somewhat, even at the same quality: a sharpened picture has more edge energy, and edges are what a JPEG spends bytes on. The output panel shows the opened file's size so you can compare.
