darken method
Change each pixel's color to be darker and return a new Image.
The amount
is a double value between 0 and 1.
Implementation
Future<Image> darken(
double amount, {
bool reversePremultipliedAlpha = true,
}) async {
assert(amount >= 0 && amount <= 1);
return transformPixels(
(color) => color.darken(amount),
reversePremultipliedAlpha: reversePremultipliedAlpha,
);
}