Compression gets a bad reputation because it is often done badly. A photo that looks crisp on your desktop can turn into a blocky mess after passing through the wrong tool or the wrong settings. The good news is that most visible quality loss is avoidable. It comes from a handful of predictable mistakes, and once you know them, you can compress aggressively while keeping images looking sharp.
The quality slider is not a pass/fail switch
Most compression tools present a slider from 0 to 100. It is tempting to assume that higher is always safer, but that is not how the trade-off works. Between roughly 75 and 85, the difference in visible detail is negligible for most photographs, while the file size continues to drop. Pushing the slider to 100 often doubles or triples the file size for a difference no one will notice on a screen.
Start around 80. Look at the result at normal viewing size, not zoomed in. If edges look clean and gradients do not show banding, you can usually go lower. If you see blocky patches in smooth areas like skies or skin, raise it slightly.
Quick tip: Always check the compressed image at the size it will actually appear on screen. Zooming in to 400% will show artifacts that no viewer will ever see.
Match the format to the content
Compression settings matter less than choosing the right format for the image. JPEG is designed for photographs and handles continuous tones well. PNG is lossless and better suited to screenshots, logos, and images with sharp text or transparency. Using PNG for a photograph produces a file several times larger than necessary with no visible benefit. Using JPEG for a screenshot with text introduces fuzzy edges around the letters.
WebP is a modern option that can handle both lossy and lossless compression. For photographs, lossy WebP typically produces files 25 to 35 percent smaller than JPEG at comparable quality, and it supports transparency. The main caveat is workflow: some older desktop viewers and editors still do not open WebP files natively. For web delivery, browser support is now broad enough that WebP is a safe default in most cases.
Do not re-save the same JPEG repeatedly
Every time you open a JPEG and save it again, the compression is applied once more. Details are discarded at each pass, and the artifacts accumulate. If you need to edit an image, work from the original file and export to JPEG only once at the end. Converting a JPEG to PNG does not restore the lost data. It only makes the file larger.
Check the dimensions before compressing
A common mistake is compressing a 4000-pixel-wide photo that will display at 800 pixels. No amount of quality tuning will recover the file size wasted on pixels that are never shown. Resize to the largest size the image will actually appear at, then compress. The combination of sensible dimensions and moderate quality usually produces the biggest savings.
A quick workflow
- Start with the original file, not a copy that has already been compressed.
- Resize to the display dimensions you actually need.
- Choose the format: JPEG or WebP for photos, PNG for graphics with text or transparency.
- Set quality around 80 for lossy formats and check the result at normal size.
- If the file is still larger than you need, lower the quality by small steps rather than jumping to a low value.
You can try these steps directly with the Image Compressor, which lets you adjust quality and compare the result side by side before downloading. If you need to change formats as well, the Image Format Converter handles JPG, PNG, and WebP in one step.