What is this calculator?
Converts a PNG image to JPEG in your browser. JPEG is usually far smaller for photographic content, at the cost of lossless fidelity and transparency — transparent pixels are composited onto white.
Use it when:
- A photograph was saved as PNG and the file is unnecessarily large.
- An upload requirement specifies JPEG.
- You need a smaller file and the image has no transparency worth keeping.
Intended for: Anyone reducing the size of a photographic PNG or meeting a JPEG-only requirement.
How is this calculated?
- The file you choose is read only for its type and name — nothing is uploaded, and the image itself never leaves your device.
- The tool validates that the source format is supported and that the requested output format and quality are valid together, producing a deterministic conversion plan: output format, quality, output file name, and the transparency and metadata policies that will apply.
- The output file name is derived from the source name with its extension replaced, so the result is predictable rather than randomly named.
- Your browser then decodes the image, draws it to a canvas at its original dimensions, and re-encodes it in the target format using its own built-in encoder.
- Because the image is decoded to raw pixels and re-encoded, the output carries only pixel data — embedded metadata such as EXIF is not preserved.
- Because JPEG has no alpha channel, the canvas is filled with white before the image is drawn, so PNG transparency is resolved deterministically rather than left to the encoder.
Example
Converting a photographic `screenshot.png` to JPEG at quality 0.9.
- The canvas is filled white, then the PNG is drawn over it.
- The output name becomes `screenshot.jpg`.
Result: `screenshot.jpg` at quality 0.9 — typically a large size reduction for photographic content, though text and sharp edges will soften.
Frequently asked questions
Should I convert a screenshot from PNG to JPEG?
Usually not. JPEG compresses smoothly varying photographic detail well, but it produces visible ringing around the sharp edges of text and user-interface elements. Keep screenshots as PNG, or use WebP.
Why did my transparent background turn white?
JPEG has no transparency support. The tool composites transparent pixels onto white so the result is predictable. Convert to WebP if you need to keep the alpha channel and still reduce size.
What does the quality setting actually do?
It controls how aggressively a lossy encoder discards detail. Values around 0.8 to 0.92 are usually indistinguishable from the original at a fraction of the size; below about 0.7, compression artefacts become visible around edges and in flat areas.
Is my image uploaded anywhere?
No. The image is decoded and re-encoded by your own browser. It is never transmitted to a server, and nothing is stored after you leave the page.
Assumptions
What this calculator takes as given:
- Conversion happens entirely in your browser; the image is never uploaded to or stored on a server.
- Pixel dimensions are preserved exactly — the tool changes the format, not the size.
- The quality setting applies only to lossy encoders (JPEG and WebP); PNG is always lossless.
- Encoding uses your browser's own image encoder, so the exact output bytes can differ slightly between browsers.
- Transparent pixels are composited onto a white background.
Limitations
What this calculator cannot know or does not model:
- Metadata such as EXIF, GPS coordinates, and colour profiles is not carried over — useful for privacy, but a loss if you needed it.
- Resizing, cropping, rotation, and other edits are outside the tool's scope.
- Animated images are converted as a single still frame.
- Very large images may exhaust browser memory, since decoding happens in the page.
- The final file size depends on your browser's encoder and cannot be predicted before encoding.
- Transparency cannot be preserved, because JPEG has no alpha channel.
- JPEG compression visibly degrades text and sharp edges; PNG or WebP is better for such images.