What a JPG to PNG conversion does, and does not, do
A JPG file stores an image as quantised DCT coefficients (ISO/IEC 10918, the JPEG standard). Once a photo has been saved that way, the fine detail that was rounded away is gone for good. This converter decodes the JPG into pixels, draws them onto a canvas of exactly the same width and height, and asks the browser to encode the canvas as PNG. PNG then stores those already-decoded pixels without any further loss, using row filters plus DEFLATE (RFC 2083, later the W3C PNG specification).
So the result is a bit-for-bit faithful copy of what the JPG looked like on screen, including its blocky edges and ringing around text. It is not a cleaner image. The real benefit is what happens afterwards: you can edit and re-save a PNG a hundred times and it will never degrade further, whereas every re-save of a JPG adds another round of loss.
Worked example
A 4032×3024 photo has 12,192,768 pixels. Decoded, that is 48.8 MB of raw RGBA data. The JPG of it might be 2 to 4 MB, because JPG throws away colour detail and high frequencies. The PNG must keep all 12 million pixels exactly, and photographic noise compresses poorly with DEFLATE, so expect roughly 15 to 25 MB. Treat these figures as ballpark; they depend on how noisy the picture is. A flat 1200×630 banner with a few solid colours behaves the other way: the PNG can be smaller than the JPG.
Things worth knowing
| Question | Answer in this tool |
|---|---|
| Is there a quality slider? | No. PNG is lossless, so the converter has nothing to tune. |
| Does the PNG get transparency? | It has an alpha channel, but every pixel is fully opaque because a JPG never had transparency. |
| Does the pixel size change? | No, the output matches the input dimensions. |
| What is the download called? | Your original name with the new extension, for example photo.png from photo.jpg. The button shows the exact byte size. |
Common mistakes
- Expecting a white background to become transparent. Converting to PNG does not cut out the subject. A JPG logo on white becomes a PNG logo on white. Removing the background needs an image editor.
- Converting to save space. For photographs, PNG is nearly always bigger. If the goal is a smaller file, stay with JPG and use the Image Compressor.
- Using it as a repair step. Upscaling or converting a heavily compressed JPG does not remove artefacts. Start from the original source file if you still have it.
- Losing the camera data. Pixels are redrawn on a canvas, so EXIF fields such as GPS position and camera model are not copied to the PNG. That is useful for privacy but means the metadata cannot be recovered from the output.
When the destination is a web page and not an editor, WebP usually gives a smaller file than either format. To go back the other way with a size cap, use PNG to JPG.