Real Cool Alpha

[jules_gaillard]

Hi,

i’m getting a bit crazy here as I cant never have real alpha cutout on my renders.
Whatever I try I always get an edge all around, even when using Cache>Remove Stroke (that is for me a non-solution : they shouldnt be here).

Am I the only one here getting tropuble with alpha cutout ?

Thank you !

[cecofuli]

You have to render with black background.

[jules_gaillard]

@cecofuli

You have to render with black background.

Really ?

[maru]

Yes, really:
https://forum.corona-renderer.com/ Alfa channel isn't completely transparent #msg107040

[Jadefox]

i’ve noticed with volumetrics on the black overide is not completely black, obviously it has a haze to it
Would this impact the above ?

[jules_gaillard]

@maru

Yes, really:
https://forum.corona-renderer.com/ Alfa channel isn't completely transparent #msg107040

Thanks to both of you, i’m trying right now (on a final render )

[njen]

And remember if you need to grade or colour correct an image with alpha, first you must unpremultiply the image, then grade, the premultiply the image, otherwise you will be colour correcting the partially transparent pixels incorrectly.

[jules_gaillard]

@Njen

And remember if you need to grade or colour correct an image with alpha, first you must unpremultiply the image, then grade, the premultiply the image, otherwise you will be colour correcting the partially transparent pixels incorrectly.

Mmm not sure to understand…

But, actually rendering on a black BG worked well, thank you !
It’s not very convenient (imo) because :

• it adds a setting to get what the alpha is made usually for
• when using a black BG, it’s visually disturbing while rendering to have a black sky for example (and much more to use Lightmix as a correct exposure of the sky is imo important for an overall correct exposure)
• if a client want finally to change your sky but you rendered without a black BG, you’re trapped.

[Juraj_Talcik]

Imho this was always a very poor limitation that could possibly be bypassed by introducing a pass that will act as if black override exists in the background but is at same time replaced by the actual Sky.
This would also alleviate the issue with Bloom&Glare which doesn’t exist with black override. The current work-around forces you to choose and brings in ton of drawbacks. It’s poor.

The second issue than Njen writes can be bypassed if you use mask as opposed to multiplication. (So for example in Photoshop, load you image as “with alpha” option and then use that alpha as mask, not opacity).

[jules_gaillard]

@Juraj Talcik

Imho this was always a very poor limitation that could possibly be bypassed by introducing a pass that will act as if black override exists in the background but is at same time replaced by the actual Sky.
This would also alleviate the issue with Bloom&Glare which doesn’t exist with black override. The current work-around forces you to choose and brings in ton of drawbacks. It’s poor.
>>> this is typically what Alpha channel is made for no ?

The second issue than Njen writes can be bypassed if you use mask as opposed to multiplication. (So for example in Photoshop, load you image as “with alpha” option and then use that alpha as mask, not opacity).
>>> I always work with alpha as a mask, I don’t even know how to use it as opacity…