In a digital image, every pixel is made up of multiple "channels." The RGB channels store the intensity of red, green, and blue (8 bits each, 0–255), while the alpha channel stores that pixel's opacity (0 = fully transparent, 255 = fully opaque).
A standard PNG-32 image has four channels — R, G, B, and A — at 8 bits each, for 32 bits per pixel. That's where the name "PNG-32" comes from.
| Alpha value | Opacity | Visual effect |
|---|---|---|
| 0 | 0% | Fully transparent (invisible) |
| 64 | 25% | Faint translucency |
| 128 | 50% | Semi-transparent |
| 192 | 75% | Dense translucency |
| 255 | 100% | Fully opaque |
This is the result of anti-aliasing. When an object's contour crosses the pixel grid, a single pixel may be partly foreground and partly background. To keep the result visually smooth, cutout tools assign these edge pixels an intermediate alpha value.
For example, if a pixel is 60% inside a strand of hair and 40% over the background, its alpha is roughly 153 (255 × 0.6). That's why high-quality cutout edges show a gradual gray ramp — it isn't noise, it's precise translucency information that preserves the edge detail of the original image.
This common concept in graphics programming determines how RGB and alpha are stored together:
"Removing the background" is essentially the act of generating a high-quality alpha mask. The binary mask output by a segmentation model (only 0s and 255s) is refined — with guided filtering and similar techniques — until edge pixels carry continuous alpha values, producing a smooth transition.
White pixels along the edge after a cutout usually mean the alpha values are imprecise, or that background color bled into the edge pixels. Fix: use the Edge Cleanup feature.
Some software doesn't support alpha channels (Windows Paint, for example) and fills transparent pixels with white on save. Always save in PNG-32 format.
A genuinely semi-transparent object has intermediate alpha values (say 100–200) by nature. That's physically correct, not a cutout error. Don't try to force these regions to fully transparent or fully opaque.
After removing a background, switch the preview background to the transparency checkerboard — how clearly the checkerboard shows through each edge pixel directly reflects its alpha. If you can't see the checkerboard along an edge, alpha is close to 255 (opaque); if it shows through clearly, alpha is lower.