compress static method

CompressionResult compress(Uint8List bytes, { double quality = 0.85, bool preserveAlpha = false, })

Compresses raw image bytes using quality-based quantization and stride downsampling.

bytes — Raw image byte buffer (grayscale or RGBA pixel data). quality — Quality factor from 0.0 (max compression) to 1.0 (no compression). preserveAlpha — If true, preserves every 4th byte (alpha channel) unmodified.

Implementation

static CompressionResult compress(
  Uint8List bytes, {
  double quality = 0.85,
  bool preserveAlpha = false,
}) {
  final stopwatch = Stopwatch()..start();
  final clampedQuality = quality.clamp(0.05, 1.0);

  if (bytes.isEmpty || clampedQuality >= 0.99) {
    stopwatch.stop();
    return CompressionResult(
      compressedBytes: bytes,
      originalSize: bytes.length,
      compressedSize: bytes.length,
      compressionRatio: 1.0,
      qualityUsed: clampedQuality,
      elapsed: stopwatch.elapsed,
    );
  }

  // Step 1: Quantization — reduce color depth based on quality
  final quantizationBits = _qualityToQuantizationBits(clampedQuality);
  final quantized = _quantizeBytes(bytes, quantizationBits, preserveAlpha);

  // Step 2: Stride downsampling — skip pixels based on quality
  final step = _qualityToStride(clampedQuality);
  final Uint8List compressed;
  if (step <= 1) {
    compressed = quantized;
  } else {
    final result = <int>[];
    for (int i = 0; i < quantized.length; i += step) {
      result.add(quantized[i]);
    }
    compressed = Uint8List.fromList(result);
  }

  // Step 3: Run-length encoding for repeated byte sequences
  final rleCompressed = _applyRle(compressed, clampedQuality);

  stopwatch.stop();
  return CompressionResult(
    compressedBytes: rleCompressed,
    originalSize: bytes.length,
    compressedSize: rleCompressed.length,
    compressionRatio:
        bytes.isNotEmpty ? rleCompressed.length / bytes.length : 1.0,
    qualityUsed: clampedQuality,
    elapsed: stopwatch.elapsed,
  );
}