I am new on an old software project. A part of this is to display a grey scaled bitmap (scanned documents). I have an own ImageControl I do not really understand yet but I have a OnPaint event and I use the graphics.FillRectangle(SolidBrush) to colorize some zones of the Bitmap.
The problem is this works only for colors with low alpha values. With a full alpha value, the dark (black) text information is colorized too and hidden then.
My question is: is there a brightness dependent fill option? That bright pixels are more affected than dark pixels?