Photos stored as PNG are the main reason to convert
PNG is lossless: it records every pixel exactly, using compression that works by finding repeated patterns. That is ideal for flat graphics, but a photograph has almost no exact repetition, so a PNG photo is huge. A 12 MP image can easily take 15 to 25 MB as PNG and around 3 MB as a JPG at quality 85, with no difference you can see.
Photos end up as PNG more often than you might think:
- Screenshots of photos, video frames or maps, since most operating systems save screenshots as PNG.
- Exports from design and editing tools where PNG was the default format.
- Scans saved by scanner software in a lossless format.
- Images downloaded from sites that serve everything as PNG.
Converting these to JPG is usually the single biggest size reduction available, often 80 to 90 percent.
When PNG is the better format to keep
JPG was designed in 1992 for continuous-tone photographs. It splits the image into 8×8 pixel blocks and simplifies the fine detail in each block. On sharp edges between flat colours this produces faint ripples, often called ringing or mosquito noise.
So think twice before converting:
- Logos, icons and UI graphics. Flat colour areas with crisp edges are exactly what JPG handles worst and what PNG compresses best. The JPG may even come out larger.
- Screenshots of text or code. At moderate quality, letters pick up a grey haze around them.
- Images you are still editing. Each JPG save loses a little detail; keep a PNG master and export JPG at the end.
A quick rule: if the picture came from a camera, JPG; if it was drawn on a computer, keep PNG or consider WebP.
What the converter does with transparency
JPG has no alpha channel, so every pixel must get a solid colour. Fully transparent areas are filled with the colour you choose in the background picker, white by default. Partly transparent pixels, such as the soft anti-aliased edge around a cut-out object or a drop shadow, are blended with that colour.
This is why the choice matters. A logo with a soft edge, flattened onto white and then placed on a dark-blue banner, shows a pale halo around its outline. Pick the colour of the place where the JPG will be used:
- White for documents, marketplaces and most product listings.
- The exact page or slide colour for images going onto a coloured background. The picker accepts any colour, and a hex value can be typed in most browsers.
- Light grey for product shots, if the shop's listing page uses that shade.
If you need to keep the transparency and still want a smaller file, PNG to WebP is the better route: WebP keeps the alpha channel and usually compresses photos far better than PNG.
Picking a quality value
The slider covers 10% to 100% and defaults to 85%. Each file shows its original and new size as soon as it is done, so you can try a value and compare immediately.
- 85% is a safe default for photos. Typical savings over PNG are 80 percent or more.
- 70–80% when you are fighting an upload limit. Smooth areas like sky can start showing faint banding toward the bottom of that range.
- 92–100% for graphics with text or sharp lines that you have decided to convert anyway. Even at 100% JPG is still lossy, but artefacts become very hard to spot.
If a photo is still too large at 80%, the resolution is the problem rather than the format. A 6000 px wide PNG export does not need to stay that wide for a web page or an email: resizing it to 2000 px wide reduces the pixel count by about 90 percent.
Under the hood
Each PNG is decoded by your browser, drawn onto a canvas filled with the background colour, and encoded as JPG, in a background worker when the browser supports it. Nothing is uploaded. The pixel dimensions do not change. PNGs with 16 bits per channel are reduced to the standard 8 bits that JPG uses, which makes no visible difference for normal viewing. Text chunks and other metadata embedded in the PNG are not carried over.
You can convert many files at once, each up to 50 MB, with the same quality and background applied to the whole batch, then download them separately or in one ZIP.