Alphablending with global alpha?

[meldaproduction]

Hi, I'm trying to optimize some graphics processing for GUI and found that things like copying images and alphablending are very fast. However what I need is alpha composition of 2 images, where the target's alpha is not important (that I think is possible), source's alpha is used, AND also a global alpha is used to multiply the source's alpha. So:

DST = DST * (1 - SRCA * GLOBALALPHA) + SRC * (SRCA * GLOBALALPHA)

I think it is pretty basic. The source image has its own alpha (like imagine a button with round borders), but I may want the button to be not completely opaque. Is there a way to do that?

There is AlphaComp, which uses image's alpha. And there is AlphaCompC which uses predefined alpha, but I need both at once.

Cheers!

[meldaproduction]

This reminds me - would it be possible to implement something like AlphaBlend in Windows API? I mean, IPP's implementation of simple alphablend is faster, but it would need the global alpha and possibility to resize the output, linear interpolation is just fine. I think this would be very handy for many people and save A LOT of CPU time...

[Ying_H_Intel]

Hello,

Thanks for let us know. I will escalte the request to our product definition database and get back to you if there are any updates.

Thanks
Ying

[meldaproduction]

Thank you Ying!

Cheers!

[gol]

I've been trying to get this to work for an hour, trying to find where my mistake was.. I didn't know it was simply not possible (while indeed pretty basic)

[Ying_H_Intel]

Hi Gol,

Could you please attach your code so we may see if there is some problem?

Best Regards,
Ying

[gol]

Hi,

well there's no code, since as I read it's not supposed to be featured.

Like the OP I needed alphablending of a premultiplied source onto a target, in which both the source's own alpha channel & a global alpha are used. This is normally the most basic use for alphablending, when you wanna draw a masked image onto another.

Weirdly everything I find on the net uses the source's alpha channel, or a global alpha, but rarely both (like the GDI's AlphaBlend does).

IPP allows doing it in 2 passes, though.

[Ying_H_Intel]

Dear All,

Just check if the feature is still interesting?   As if it is very rare used, then we may not implement it. 

Thanks

Ying