MATLAB: How to detect a dark color in RGB triplet


I am plotting a map with many subdivision and colors.
I would like to automatically draw the borders with contrasting color with respect to the facecolor of the subdivision.
I am using the sum of the RGB triplet but I am not having perfect matchs.
Is there another way to do that?
My results until now:

Best Answer

  • I don't know what you do on the border between light and dark regions. But anyway, when you're drawing the boundary around a region get the mean RGB of that region -- summing the values is fine, or equvalently, taking the mean. Then you can say
    meanRGB = mean([regionsRedValue, regionsGreenValue, regionsBlueValue]);
    if meanRGB < 128
    % It's dark, so draw with white line.
    lineColor = 'w';
    % It's bright, so draw black line.
    lineColor = 'k';
    plot(x, y, '-', 'Color', lineColor, 'LineWidth', 2);