Nothing is uploaded, and that has a cost
None of these tools has a server that receives your files. The image compressor and the image converter draw your picture onto the browser Canvas API and re-encode it in the format you pick; image to Base64 reads the file straight into a string. No network request leaves the page, which is why these pages keep working with the connection off and why a scanned contract, an ID photo or a screenshot full of personal data is safe to drop in. Close the tab and the memory is released.
The cost is that the work runs on your own hardware. Compression and conversion accept up to 10 MB per file, Base64 is stricter at 5 MB, and all three suggest no more than 50 files in one go. A phone or an older laptop will visibly stall on a few dozen large photos. All three can package a finished batch into a single ZIP, so you are not saving files one at a time.
What compression actually changes
- Lossy (JPG, WebP): real detail is thrown away to buy a smaller file. Around 80 percent quality the difference is usually invisible, but what is discarded never comes back. Compressing an already compressed file only makes it worse, so keep your originals and re-export from them.
- Lossless (PNG): only the encoding changes, every pixel survives. That is why the quality slider is disabled once you choose PNG in the compressor. The only lever left is the maximum width.
- Not compression at all (Base64): encoding a file as text changes no pixels and saves no bytes. It adds about 33 percent.
If you want a genuinely smaller file, resize first. A phone photo is often 4000px wide while the page that displays it is 800px. Capping the width at 1920px saves far more than dragging the quality slider down.
One side effect is worth knowing before you archive anything: re-encoding through a canvas drops embedded metadata, so the capture date, camera model and GPS coordinates the camera wrote are not carried into the output. That is a quiet privacy win before you post a photo publicly, and a problem if you sort your library by those fields. Keep the original either way.
Picking JPG, PNG or WebP
- Photographs: WebP gives the smallest file, JPG is the safest. Older Office versions and some legacy systems still cannot open WebP, so send JPG when the file is going to somebody else.
- Transparency: PNG or WebP. Converting to JPG fills transparent areas with white, because JPG has no alpha channel. Nothing is broken, the format simply cannot store it.
- Screenshots, text and line art: PNG. Lossy encoding smears a halo of noise around letter edges that is very hard to unsee.
AVIF is not supported.Browser support arrived late and unevenly, so the converter stops at JPG, PNG and WebP. HEIC from an iPhone depends on whether your browser can decode it: Safari on a Mac or an iPhone generally can, while Chrome on Windows usually fails to read the file at all. If you convert HEIC often, the least painful fix is on the phone, under Settings then Camera then Formats, where “Most Compatible” makes new photos JPG from the start.
When inlining Base64 helps
A data URL is self-contained, which is the whole appeal: the image travels inside the HTML, CSS or Markdown instead of alongside it, and costs no extra request. The same property is the drawback. An inlined image is downloaded with the document every time, cannot be cached on its own, and is about a third larger than the file it came from.
The rule of thumb is simple. Small, used once, and needs to travel with the document: inline it. Large, or reused across several pages: leave it as a file and let the cache do its job. A common cut-off in build tools sits around 8 KB. HTML email and a report that has to stay a single file are the two cases where inlining earns its keep. If the string looks too long, the order matters: compress first, then encode, never the other way round.
Common questions
Are my images uploaded to a server?
No. All three tools work inside your browser. The compressor and converter re-encode through the Canvas API and the Base64 tool reads the file locally, so no network request is made and the pages still work offline. Closing the tab releases everything.
What is the difference between the compressor and the converter?
The compressor changes quality and maximum width to make the file smaller. The converter only changes the format and keeps the original dimensions. Use the compressor for size and the converter when the recipient simply cannot open your file. Image compressor
Why did my transparent background turn white when I saved as JPG?
JPG has no alpha channel, so transparent pixels are painted onto a white background during conversion. Choose PNG or WebP if the transparency needs to survive. Image converter
Can I convert AVIF or an iPhone HEIC file?
AVIF is not supported. HEIC depends on your browser: Safari on Apple devices can usually decode it, while Chrome on Windows normally fails to read the file. On an iPhone you can set Settings, Camera, Formats to Most Compatible so new photos are saved as JPG. Image converter
Why is my Base64 string larger than the original image?
Base64 turns every three bytes into four ASCII characters, which adds roughly 33 percent, plus the data:image prefix. It is an encoding, not a compression format, so shrink the image first if size matters. Image to Base64
Does compressing or converting keep EXIF data?
No. Re-encoding through a canvas drops embedded metadata, so capture time, camera model and GPS coordinates are not in the output file. Keep the original if you need that information, and treat the stripping as a bonus when you are sharing a photo publicly.
Why did my file get bigger after converting to WebP?
If the source was already a heavily compressed low quality JPG, re-encoding it as WebP can end up the same size or slightly larger. WebP saves the most when the source is a PNG or a high quality JPG.