Set dimensions before compression
If an image is 5000 pixels wide but only displayed in a 900-pixel space, resizing it may save more bytes than lowering quality alone.
Choose a target size that still works for the largest display context. Keep a higher-resolution source for later uses.
Compare one change at a time
Start with the format that fits the image. For a photograph, compare a moderate JPEG or WebP setting; for line art or transparency, check PNG or lossless options in a dedicated encoder.
Lower the quality slider gradually. Inspect small text, sharp edges, skin tones, and smooth gradients. A single file-size number does not show where artifacts appeared.
Keep the source and re-check the destination
Repeatedly saving a lossy file can accumulate visible artifacts. Re-export from the original when possible.
Check the final file in the context where it will be used. Upload limits, color profiles, metadata, and format support can differ between platforms.
Common questions
Is the smallest file always best?
No. A very small file may show banding, ringing, or smeared texture. Balance visual quality with the destination's size constraints.
Why is PNG quality unchanged?
PNG is encoded losslessly by this browser canvas workflow and the quality parameter does not apply to PNG output.
References
Sources explain browser behavior or guidance; they do not verify a particular output file.