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Re: Map transparent image [message #35683 is a reply to message #35681]

Tue, 01 July 2003 12:22

mmiller3
Messages: 81
Registered: January 2002

Member

>>>> > "Haje" == Haje Korth <haje.korth@jhuapl.edu> writes:

> I am trying to overlay a grey-shaded mask over an image to
> indicate areas where sample data are less
> reliable. However, I want the grey shaded area to be
> transparent so that I can still see the underlying data
> points.
...
> Does anyone know, how the mask can be worked into the image
> prior to display? What is the math that one would apply?

One method that you might like is alpha blending. If you have
two images with two different colors (from two color maps say),
calculate a new color map like

RGB = BYTE( alpha * FLOAT(baseRGB) + (1.0 - alpha) * FLOAT(overlayRGB) )

where the *RGB are RGB 3-tuples. You can do this by hand, so to
speak, in your own code if you are using direct graphics, or you
can use the alpha blending that is built into object graphics.

Mike

--
Michael A. Miller mmiller3@iupui.edu
Imaging Sciences, Department of Radiology, IU School of Medicine

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[Message index]

		Re: Map transparent image By: Haje Korth on Tue, 01 July 2003 12:50
		Re: Map transparent image By: Haje Korth on Tue, 01 July 2003 12:49
		Re: Map transparent image By: Haje Korth on Tue, 01 July 2003 12:43
		Re: Map transparent image By: David Fanning on Tue, 01 July 2003 12:51
		Re: Map transparent image By: mmiller3 on Tue, 01 July 2003 12:22
		Re: Map transparent image By: Andy Loughe ( remove on Tue, 01 July 2003 07:46
		Re: Map transparent image By: David Fanning on Tue, 01 July 2003 11:12
		Re: Map transparent image By: Haje Korth on Tue, 01 July 2003 10:45
		Re: Map transparent image By: David Fanning on Tue, 01 July 2003 08:26
		Re: Map transparent image By: Haje Korth on Tue, 01 July 2003 08:04
		Re: Map transparent image By: David Fanning on Tue, 01 July 2003 06:24

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