PNG Background Remover

PngBackgroundRemover.cs

// > dotnet run PngBackgroundRemover.cs
// requires .NET SDK 10+
// MIT License: https://gist.github.com/saulm314/985a47c7683d0cd9429f8a2938457562

#:package [email protected]

using BigGustave;

// configure these constants as required
const string InputPngPath = "string-base.png";
const string OutputPngPath = "string-base-nobg.png";
const byte R = 42, G = 42, B = 42;

// don't touch anything from here on, unless you know what you're doing

Pixel backgroundPixel = new(R, G, B);
Png inputPng = Png.Open(InputPngPath);
PngBuilder builder = PngBuilder.Create(inputPng.Width, inputPng.Height, hasAlphaChannel: true);
for (int x = 0; x < inputPng.Width; x++)
{
    for (int y = 0; y < inputPng.Height; y++)
    {
        Pixel oldPixel = inputPng.GetPixel(x, y);
        Pixel newPixel = PixelEqualsRGB(oldPixel, backgroundPixel) ? new(0, 0, 0, 0, isGrayscale: false) : oldPixel;
        builder.SetPixel(newPixel, x, y);
    }
}
PngBuilder.SaveOptions saveOptions = new() { AttemptCompression = true };
byte[] outputPngBytes = builder.Save(saveOptions);
File.WriteAllBytes(OutputPngPath, outputPngBytes);

static bool PixelEqualsRGB(Pixel pixel1, Pixel pixel2) => pixel1.R == pixel2.R && pixel1.G == pixel2.G && pixel1.B == pixel2.B;

~LICENSE

MIT License

Copyright (c) 2025 Saulius Markevicius

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

~README.md

PNG Background Remover

This script removes the background from a PNG file. Specify the input PNG file path, the output PNG file path, and the RGB value for which background colour to remove. It sets all pixels that match that exact RGB value (and any opacity) to an RGB value of 0,0,0 and an opacity of 0. Any pixels that had even a slightly different colour are untouched.

If you find a bug feel free to drop a comment below and I'll see if I can fix it.