[tanguy]

Hi all, have you this problem to ?
When we render a scene with the alpha and ID mat and ID Mesh, the sky isn't process in the output bitmap...
The sky is processing in the light computing but not in the raterisation pipe... No sky in the render output... blurp

Some body have the same problem ?

[deadalvs]

yep, that's official.

since NL say that if an alpha is required, the sky color is «not useful for the user», thus just displayed black.
i don't get this point either

but yes, that's the way it is - at the moment.

[tom]

It's not about the sky is not useful so it's rendering black. It's a technical must in compositing. Only with using alpha you can't crop the background perfectly because the sky will always appear in the pixels where you have blur due to dof or even on AA pixels when the edge is sharp. So, it will make your composition fail. This is one of the most common mistake in compositing. Instead the RGB channels comes pre-multiplied with black so you can easily unmultiply black using alpha in compositing applications.

[deadalvs]

this clears the thought a bit more precise ...

but i think this should be an option for people that need both the alpha and the sky's color for post-work (even with this draw-back).

[tom]

It's not a draw-back, it's a real mistake which you should strictly avoid doing when doing compositing. If you still need to render the sky, you can render the channels apart. It won't take longer time in sum.*

(*) See below: http://www.maxwellrender.com/forum/view ... 341#234341

[bakbek]

It's not a draw-back, it's a real mistake which you should strictly avoid doing when doing compositing. If you still need to render the sky, you can render the channels apart. It won't take longer time in sum.

I think it's about being used to something that works fine and then changed when it can actually be kept us an option for the user.

[tom]

bakbek, technically wrong is wrong, assuming that's working fine is rejecting the ways of doing things correctly in the industry standards.

[Mihai]

Alpha wasn't working fine before, and like tom said, this is how it's supposed to be done for the alpha to composite perfectly, especially with Maxwell where dof is a natural consequence of the camera. Even if you had no dof at all, the sky would creep in on the AA edges and your composites would fail.

[mashium123]

OK, I'll go on and out myself as the slowest of this class...
I just don't get it... how do you composite the maxwell output?

I receive two files when I tick RGB & Alpha channels in the output channels tab.
This is the first file. It has the filename, I used originally...


This one is the second file. It has the original filename plus "_alpha" at its end:


And this is just an example of an artificial sky that I want to have as background:


I just can't put them together, that
a) the lower part is the plane, cube and sphere & the upper part the artificial sky
b) the lower part is the plane, cube and sphere & the upper part the maxwell sky (yes sometimes I would like to have it.)

Would anyone help me? (Is this off the topic? Sorry, if it so.)

[tom]

Here's how...
http://www.divshare.com/download/1049243-06a

[mashium123]

Wow... now how nice is that...

Thanks so much, Tom. Feels like a mighty door opened up...

[deadalvs]

hmm.

from the technical point of view it's all clear.

but to get both a «clear» alpha and color map, the image has to be rendered twice, since the alpha is also SL-dependent and needs time to clear up.

just a few days ago i had to render an image around 3400x2400 px with 6 million polys (with two large trees). so i rendered the color channnel but i also needed the alpha... so again: rendering it a few hours to get a near-non-noisy alpha.

or how did You mean «it won't take longer in sum», Tom ... ?

[Mihai]

The first render, render only the color image, no alpha. The second render, check only alpha, and uncheck the main render. This way it takes the same time as if you had rendered everything in one go.

[tom]

Well, sorry it was my mistake telling you it would be the same time. Because, during the test stage without optimizations it was taking same time and this is why Mihai confirms as well, but now I remember important optimizations have been done just before the release and yes, the interleaved mode is rendering faster than you render them apart. Sorry for the confusion.

[Mihai]

Just to be absolutely clear, if you will have this option (to render sky and alpha at the same time), don't expect your alphas to crop out the image as you expect. You are basically asking for an option which will provide an incorrect alpha cutout, which will make edges appear where the sky color blends with the edges of an object.