ImageAttributes question

[C# Programming]

I'm alreay familiar with Bitmap function: MakeTransparent() which sets one color to be transparent. I would like to go a step further and enable the user to adjust the transparency range around the selected transparency color. I'm currently using the ImageAttributes class for modifying bitmaps and I was hoping to use it for setting the transparency range. I see that there is SetThreshold() and SetColorKey() but I don't know how to use these to set a color range that encompasses hue, saturation and brightness differences.

Any suggestions?

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