How to change Text color based on background Image - Flutter

Question

I want to change text (and Icon) colors based on the background image for visibility.

I've tried: Using palette_generator package, to check the Dominant Color of the background Image and useWhiteForgroundForColor function (returns a bool) from flutter_statusbarcolor package to select black or white color for the my text (and Icon) colors.

The Problem: Sometimes dominant color turns out null. In my tests, this happens with black and white colors and I don't know of any ways to find out which one.

Future<bool> useWhiteTextColor(String imageUrl) async {
  PaletteGenerator paletteGenerator =
      await PaletteGenerator.fromImageProvider(
    NetworkImage(imageUrl),

    // Images are square
    size: Size(300, 300),

    // I want the dominant color of the top left section of the image
    region: Offset.zero & Size(40, 40),
  );

  Color dominantColor = paletteGenerator.dominantColor?.color;

  // Here's the problem 
  // Sometimes dominantColor returns null
  // With black and white background colors in my tests
  if (dominantColor == null) print('Dominant Color null');

  return useWhiteForeground(dominantColor);
}

I found other methods for other languages, but I don't know a way to implement the same method in dart.

Additional note: My actual code includes some additional complications. I am using a SliverAppBar and here I want to determine the title and icons colors for when the flexibleSpace is expanded. I change their colors when collapsed with the help of the community based on this.

Answer 1

the color class already has a method to calculate luminance, called computeLuminance()

Color textColor = color.computeLuminance() > 0.5 ? Colors.black : Colors.white;

Answer 2

i use the below method to find out which one to be used (either black or white).

Color getTextColor(Color color) {
int d = 0;

// Counting the perceptive luminance - human eye favors green color...
double luminance =
    (0.299 * color.red + 0.587 * color.green + 0.114 * color.blue) / 255;

if (luminance > 0.5)
  d = 0; // bright colors - black font
else
  d = 255; // dark colors - white font

return Color.fromARGB(color.alpha, d, d, d);   }