Is this tool free?
Yes. Flatten PNG Transparency is free to use and runs entirely in your browser with no account needed.
Does it convert the image to JPG?
No. The output stays a PNG. The only change is that transparency is replaced with the visible background you choose before export.
Can I use a gradient instead of a solid color?
Yes. The tool supports a simple two-stop linear gradient with a few direction presets, in addition to white, black, and custom solid colors.
Does the compositing happen locally?
Yes. The source file stays in your browser the whole time, and the flattened PNG is generated on your device without any upload.
Does it work on mobile?
Yes. Because it runs in the browser, you can flatten a PNG on a phone or tablet just as easily as on a desktop.
Why would I flatten a PNG instead of just converting it to JPG?
Because you want to control what fills the transparent area. A JPG converter that discards alpha typically composites onto white or, worse, onto black, without telling you. Flattening first means you choose the color, verify the result, and then convert. It also lets you keep a lossless PNG if the artwork is flat graphics where JPG would introduce ringing around the edges.
Does flattening reduce the file size?
Not reliably. PNG compression is driven by how much repetition is in the pixel data, not by whether an alpha channel is present. Filling the transparent area with one flat color compresses well and can shrink the file. Filling it with a gradient adds thousands of distinct values and usually makes the file bigger.
Can I get the transparency back afterwards?
No. The alpha information is consumed in the composite and the exported file is fully opaque. If you later need the cutout again, you have to start from the original transparent PNG, which is why you should always keep it. Reconstructing a matte from a flattened image is a much harder problem than flattening was.
What background color should I flatten onto?
Whatever the destination surface actually is. If you do not know, white is the safe default for print and documents, and it matches most page backgrounds. Run the asset through the PNG Background Tester first if you want to see what the edge looks like on several candidates before committing to one.
Does the compositing run on my device?
Yes. The background is drawn and your PNG is composited onto it on a canvas in the page, then re-encoded locally. Nothing about the image is transmitted. The only network call is a credit counter carrying the tool name.