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Drythe

Transparency without alpha channel

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Is it possible to use a certain color in a bitmap to use transparency with different levels of opaqueness? Like if you have an image over a black background with smooth transition into the black, can you use the black values as various levels of transparency (full black being completely transparent)?

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Quote:
Original post by Drythe
Is it possible to use a certain color in a bitmap to use transparency with different levels of opaqueness? Like if you have an image over a black background with smooth transition into the black, can you use the black values as various levels of transparency (full black being completely transparent)?



shade of black are greys.

How do you smooth transition into 'black' without keeping the components of the regular colors.

maybe you mught be able to use some way to interpret the near black values, but it sould have to build an alpha channel value in memory for the graphics routines to do the transparencies blend operation.

editing the picture and controlling your 'near black' colors will be nasty. at this point you might as well do a seperate alpha mask and feather it.

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For certain effects, like explosions and fire, you can sometimes use additive blend with decent results. This always makes the image brighter and can look bad if abused, and the nVidia GPU book suggests that fire is best produced with a traditional blend. But additive blending will work with the types of images you speak of, with gradual transitions into black. Other than using alternate blend modes, the information just isn't there to do what you describe.

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