Compression · Knowledge
How Image Compression Works
When you compress a photo in the browser, the tool reads the image, optionally resamples color for the target format, and writes a new file at a quality or effort setting you choose.
Quick take: Image compression re-encodes pixels. Lossy settings shrink photos the most; lossless settings protect graphics and text.
Photos (JPEG / lossy WebP)
The encoder groups similar colors and throws away subtle differences. Lower quality = smaller file and more blockiness or softness. Start mid-high on the slider for web photos.
Graphics and screenshots
Sharp edges and flat colors hate aggressive JPEG. Prefer PNG or lossless WebP when text and UI must stay crisp — or accept a format change when size is critical.
What Format Convertly’s image tools do
The Image Compressor and format tools (JPG, PNG, WebP, HEIC, AVIF) run locally. Some paths re-encode to a smaller delivery format (for example PNG→WebP) so downloads shrink meaningfully.
Key points
- Decode → re-encode is the usual image compression path.
- Photos tolerate lossy encodes; UI text often does not.
- Resize before compressing when pixel dimensions are oversized.
Open a compressor
Shrink files privately in your browser — pick a category, then a format tool when you know the extension.
Shrink photos and graphics in your browser — format-specific tools for JPG, PNG, WebP, HEIC, and AVIF.
Related compression guides
Related quality guides
Related concepts
FAQ
Should I resize or compress first?
Resize first when the image is far larger than you need on screen, then compress. Oversized dimensions waste more bytes than quality alone.
Does PNG compression stay lossless?
True PNG packing is lossless. Some “PNG compressor” tools re-encode to WebP/JPG for bigger savings — check the output format on the tool page.
Browse all compression guides, compressors, or quality guides.