Why does a transparent PNG look white?

Place the PNG over a colored background. If the white area takes on that color, the viewer was showing its own white canvas through the PNG. If the area stays white, sample that pixel’s alpha to see whether white was saved into the file.

A check passes if it distinguishes the transparent background from the saved white background at pixel (10, 10) in the two supplied files.

Test dateTool and versionSame source or frameSetting changedResult
2026-11-14Node 24.22.1transparent-cutout.png and white-baked-cutout.png, pixel (10, 10)White canvasFail. Pixel (10, 10) was white in both files.
2026-11-14Node 24.22.1Same transparent-cutout.png and white-baked-cutout.png, pixel (10, 10)Blue canvasPass. Pixel (10, 10) became blue in the transparent file and stayed white in the other.
2026-11-14Node 24.22.1Same transparent-cutout.png and white-baked-cutout.png, pixel (10, 10)Read decoded alphaPass. Pixel (10, 10) was alpha 0 in the transparent file and 255 in the other.

Source files transparent-cutout.png and white-baked-cutout.png.

Download the parameter sheet, original PNGs and reproduction script.

See what the viewer is doing

Orange circle on the viewer's white canvasTransparent file on white
Orange circle with white pixels saved into the fileWhite pixels on white
The viewer's blue canvas shows around the circleTransparent file on blue
The area around the circle stays white over a blue canvasWhite pixels on blue
The same two original files shown on two canvas colors.

We built the pair with the same circle and white RGB background values. The only difference at the test coordinate is opacity. FFmpeg decoded both images to eight-bit RGBA and the test script read the same pixel in each. Compositing both on white gave the same RGB triplet, 255/255/255. Changing the canvas to blue made the transparent sample read 24/77/135. The opaque sample still read 255/255/255. Alpha inspection confirmed which input produced each result without depending on a canvas.

Check the area that actually looks wrong. Start inside the background, then take separate samples near the edge. A fully opaque white pixel stays white on any canvas. A partially transparent edge can look lighter on white than on dark blue, even when the background itself is transparent. Sampling one corner only tells you about that corner. If your export has a white rim, look just outside and just inside the subject's boundary before changing your export settings.

The PNG specification defines alpha as the fraction of full opacity. This experiment reads the decoded samples, which also works when transparency is represented by a palette in the source. W3C PNG specification