Compression isn't one setting — it's a format decision first
The quality slider doesn't do the same thing for every file. JPEG and WebP are lossy formats: they throw away pixel information that's statistically less noticeable to the eye, and the quality value controls how aggressively they do that. PNG is lossless — it compresses the exact pixel data with no information loss, the same way a ZIP file does, which means there's no quality dial to turn. Choosing the right output format is therefore the first decision, and it determines whether the slider even does anything.
This is why the tool disables the quality slider for PNG output rather than showing a slider that does nothing — there's genuinely no lossy/lossless trade-off to make within PNG itself.
Which format actually compresses best, by content type
| Content type | Best format | Why |
|---|---|---|
| Photos, gradients, complex scenes | JPEG (70–80%) or WebP | Lossy compression excels at smoothing subtle color variation invisibly |
| Flat graphics, logos, screenshots with text | WebP | Handles sharp edges and flat color better than JPEG's block-based compression |
| Images needing transparency | PNG or WebP | JPEG has no alpha channel at all |
| Line art, diagrams with few colors | PNG | Lossless coding is efficient when there's little color variation to begin with |
Compressing an image step by step
Drop an image (PNG, JPG, or WebP) onto the zone.
Pick an output format and drag the quality slider — the preview updates instantly so you can see the visual trade-off in real time.
Compare the original and compressed sizes shown side by side.
Click Download compressed image to save the smaller file locally.
Finding your actual quality floor
Rather than guessing a number, use the live preview as a testing loop: drag the slider down until you can just barely start to see artifacting — blocky edges in JPEG, or soft blurring in WebP — then nudge it back up slightly. That point is usually well below where people assume; JPEG at 70–80% is frequently visually indistinguishable from 100% for photographic content while being meaningfully smaller.
The transparency trap
This is the single most common failure mode with lossy compression: JPEG has no alpha channel, full stop. If you compress a PNG with transparent areas and switch the output format to JPEG, those transparent regions get filled with a solid color — typically white or black — because JPEG has no way to represent 'no pixel here.' If your source image has any transparency you need to keep (a logo, an icon, a cutout), your output format has to stay PNG or WebP; JPEG isn't an option regardless of quality setting.
Common mistakes
Compressing a PNG logo to JPEG and being surprised the transparent background turned solid — transparency and JPEG are fundamentally incompatible.
Assuming PNG is always 'higher quality' than JPEG or WebP — PNG is lossless, but for photographic content that often just means a much larger file with no visible benefit over a well-tuned lossy version.
Re-compressing an already heavily-compressed JPEG at a low quality setting — lossy artifacts stack, so a file that's been saved as low-quality JPEG multiple times degrades further each time.
Picking WebP without checking where the file is going — most modern browsers and apps support it, but some older or third-party systems (certain print workflows, older CMS uploaders) still expect JPEG or PNG specifically.
Real use cases
Shrinking phone photos before attaching several to an email with a size limit.
Compressing product photos for a website where JPEG at 75% cuts load time with no visible quality loss.
Reducing a screenshot-heavy PNG down with WebP before embedding it in a support ticket.
Preparing a batch of photos for Images to PDF where smaller source images mean a smaller final PDF.
Frequently asked questions
Q: Is image compression really free and unlimited?
A: Yes — no accounts, no watermarks, no daily caps. Compress as many images as you like.
Q: Are my images uploaded to a server?
A: No. Compression runs entirely in your browser using the Canvas API, with zero outbound upload requests.
Q: Why is the PNG quality slider disabled?
A: PNG is a lossless format with no quality setting to adjust. Switch the output format to JPEG or WebP to use the slider.
Q: What format gives the smallest files?
A: For photos, JPEG around 70–80% quality is usually smallest. For flat graphics, WebP often wins. PNG stays lossless, so it's rarely the smallest option.
Q: Why does my PNG turn black or white in places after compressing to JPEG?
A: JPEG has no transparency support, so transparent areas get filled with a solid color. Use PNG or WebP output if you need to preserve transparency.
Q: Should I always use WebP since it's usually smallest?
A: Not always — check where the image is going first. WebP has broad support in modern browsers, but some older tools, certain email clients, and some print workflows still expect JPEG or PNG specifically.
Compress your image now
Shrink your file with the Image Compressor. Need a different file format entirely? Try the Image Converter. Need to change dimensions too? Use the Image Resizer, or apply visual adjustments first with Image Filters.
