38 lines
1.3 KiB
Dart
38 lines
1.3 KiB
Dart
import 'package:image/image.dart' as img;
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/// Removes near-white background by making pixels with high RGB values transparent.
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///
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/// - Ensures the image has an alpha channel (RGBA) before modification.
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/// - Returns a new img.Image instance; does not mutate the input reference.
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/// - threshold: 0..255; pixels with r,g,b >= threshold become fully transparent.
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///
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/// TODO: optimize through SIMD or web-ffi openCV, sadly they are not stable yet.
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///
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img.Image removeNearWhiteBackground(img.Image image, {int threshold = 240}) {
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// Ensure truecolor RGBA; paletted images won't apply per-pixel alpha properly.
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final hadAlpha = image.hasAlpha;
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img.Image out =
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(image.hasPalette || !image.hasAlpha)
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? image.convert(numChannels: 4)
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: img.Image.from(image);
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for (int y = 0; y < out.height; y++) {
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for (int x = 0; x < out.width; x++) {
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final p = out.getPixel(x, y);
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final r = p.r;
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final g = p.g;
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final b = p.b;
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if (r >= threshold && g >= threshold && b >= threshold) {
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out.setPixelRgba(x, y, r, g, b, 0);
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} else {
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// Keep original alpha if input had alpha; otherwise force fully opaque.
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final a = hadAlpha ? p.a : 255;
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if (p.a != a) {
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out.setPixelRgba(x, y, r, g, b, a);
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}
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}
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}
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}
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return out;
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}
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