OnPaint event: Colorize zones on a bitmap with high alpha value

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.NET3.5

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?

Posted 19-Jul-12 22:32pm

Terkosh

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Christian Graus · Accepted Answer · 2012-07-20T12:20:00

Solution 1

No there isn't, you'd need to write one. You can read my image processing articles for ideas on detecting brighter pixels or writing a filter that modifies pixels with respect to their values ( per pixel filters )

Posted 20-Jul-12 12:20pm

Christian Graus

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Terkosh 24-Jul-12 9:02am

Thank you for your reply.
Very interesting articles. But I am lazy and found an easy way which works for me: I use for the Fillrectangle a PathGradientBrush with a ColorBlend and for the CenterColor I use the same color but with a fixed low alpha value. This works because the text information is in the center of colorized rectangle.