Pre-multiplied alpha

[victoria_beswick]

Independent of pre-multiplied alpha being active or not, when I download an image All sky is lost because always it pre-multiplies the alpha channel anyway.

[martin_dimitrov]

Premultiplied alpha is characteristic of the exported image from VRay VFB; the toggle in Collaboration is just a hint for us on visualizing the image in the browser. When downloading the image back, we provide the original image as exported, so you will need software that can work with images with premultiplied alpha.

[victoria_beswick]

Thank you for the quick reply.
Photoshop can work with Premultiplied alpha. But I can't get any sky back, there is no alpha channel or mask or setting that I can use, the sky is just entirely gone (sky from hdri placed in dome light). I would like to have a flattened image like is displaying on the browser.
At the moment what I have to do is always save a jpeg on local machine.

Edit - one way of getting the image with the sky is by right clicking and "Save image" - this way downloads a png, but the sky is included.

[martin_dimitrov]

I look at premultiplied alpha as a "trick" that renderers use; the alpha channel contains data where actual scene objects are rendered and where only sky is visible. Because sky parts are encoded with full transparency, software that is not aware of this will "remove" the sky from the image. So the alpha channel in premultiplied alpha images should be treated as a mask and compatible software ignores it before displaying the image because all pixel colors are "premultiplied" in RGB channels. This is exactly what we do when displaying these in the browser, and right-clicking "Save image" allows you to extract it.