brightness function
Implementation
void brightness(Uint8List bytes, num adj) {
adj = (adj > 1) ? 1 : adj;
adj = (adj < -1) ? -1 : adj;
adj = ~~(255 * adj).round();
for (int i = 0; i < bytes.length; i += 4) {
bytes[i] = clampPixel(bytes[i] + (adj as int));
bytes[i + 1] = clampPixel(bytes[i + 1] + adj);
bytes[i + 2] = clampPixel(bytes[i + 2] + adj);
}
}