Two newbie questions.. (alpha clipping info passes)

[caffe3]

I got a plane with an alpha image on it (Layer ID 1), and objects (Layer ID 2) that are behind it are visible in the beauty pass, but in AO and other info passes, the objects that are behind the plane with the alpha disappear/are clipped when rendering with Render Layer set to 2.

Also is it possible to render out multiple render layers in one go, or render out a render layer + layer masks (for color correcting each layer in post) in one render. Or must one use render layer + ObjectIDs? The problem I'm having is that only render layer can give a shadow and reflection pass. Also separating objects by layer masks will leave an empty 1-2pixel edge between each other if they overlap.

Any help is appreciated!

[aoktar]

Hi,
why do you want to get multiple render layers in one go? It only supports one render layer in one render session.

[caffe3]

I'm assuming if it was possible to render multiple render layers in one session it would take less time for octane to render the different render layers, than it would take to re-render the scene for each layer? Maybe that's wishful thinking though?

Object ID's might be enough though, but I can't figure out how to set the color for each object. Material ID's works though, I guess.

[aoktar]

Hi,
Render layer or masks is designed for different usages. Have you seen the Inlifethrill's free multi passes tutorials? It should be very informative about your questions.

[caffe3]

Yeah, I watched that. And he said Layer Masks was basically Render Layer but for multiple layers.

But there's multiple problems with Layer Masks:
1. You don't get the Shadows, Black Shadows, Colored Shadows and Layer reflections passes, which are pretty important in compositing.

2. The black and white mattes (layer masks) are not very useful when you have objects overlapping. If you mask the objects by their layer masks, you will get a roughly 1 pixel empty/transparent space between them.

3. You can't set layer mask for a group of objects (under a null) and then individually each object in the group. Why you'd want to do this is basically as a workaround for the problem above (2).

And the issues with Render Layer are:
A. You don't have any proper way of masking individual objects from the group of objects rendered as one layer. Other than Material ID's which cannot be set manually? Object ID's also not possible to set manually from what I can tell.

B. When rendering an object (like an apple for instance, set as Layer ID 1) behind an other object (like a window for instance, set as Layer ID 2) with an Opacity/Alpha, the apple is visible in the beauty render, but invisible/disappears in info passes like AO, Material ID's etc. when Render Layer is set to 1. Is this a glitch with Octane and not the plugin?

Thanks for the help!

[stratified]

Yeah, I watched that. And he said Layer Masks was basically Render Layer but for multiple layers.

But there's multiple problems with Layer Masks:
1. You don't get the Shadows, Black Shadows, Colored Shadows and Layer reflections passes, which are pretty important in compositing.

2. The black and white mattes (layer masks) are not very useful when you have objects overlapping. If you mask the objects by their layer masks, you will get a roughly 1 pixel empty/transparent space between them.

3. You can't set layer mask for a group of objects (under a null) and then individually each object in the group. Why you'd want to do this is basically as a workaround for the problem above (2).

And the issues with Render Layer are:
A. You don't have any proper way of masking individual objects from the group of objects rendered as one layer. Other than Material ID's which cannot be set manually? Object ID's also not possible to set manually from what I can tell.

B. When rendering an object (like an apple for instance, set as Layer ID 1) behind an other object (like a window for instance, set as Layer ID 2) with an Opacity/Alpha, the apple is visible in the beauty render, but invisible/disappears in info passes like AO, Material ID's etc. when Render Layer is set to 1. Is this a glitch with Octane and not the plugin?

Thanks for the help!

Hi,

Render layer masks is not a way to do multiple layers at once. It generates black and white masks that you can use in post to mask out objects from your scene. There's nothing revolutionary about them. Like you already noticed, they will give you edge artefacts with overlapping objects (And they certainly don't work with DOF and motion blur).

The idea of the layer is that each object you want to isolate on a separate layer. The advantage of render layers is that they can isolate your objects without the edge artefacts that masks have. You can render only 1 layer at once.

Regarding the info passes, the window is not on the active layer so it will be ignored by the rays regardless it's opacity. The exact behaviour depends on the visibility option configured in the render layer node.

cheers,
Thomas

[caffe3]

Thanks for the reply!

OK, so the workflow is to render using Render Layer multiple times when absolutely necessary. I can live with that. But how about adding another layer id type of setting in the object tag, so we can render out ONE Render Layer TOGETHER with multiple Layer Masks in one go? Either that or enable us to manually set the color of Object/Material ID's for each object/material individually.

The reason for that is, one might want to render a group of items using Render Layer to get the clean edges, but still need some type of masks/mattes to be able to isolate specific objects in post for simple stuff like color correction.

---------------------------

About the info passes, I've attached a screenshot to better explain the issue. Basically, the MAIN pass with Render Layer ticked on is displaying the image correctly, but the info pass does not match. It completely clips/masks anything behind an object with opacity, while the MAIN/beauty pass does it correctly. Surely this is considered a glitch, cause you can't really use the info passes with the beauty/MAIN pass if they don't match.

[stratified]

Hi,

Rendering multiple mask as a single pass is way too specific to hack into the render engine. Rendering masks itself is really fast, rendering all the masks would be a matter of seconds. For the standalone we can provide a script to do this but if you're using the plug, you should bring this up with Ahmet.

Thanks for the picture that clarifies things! You're right beauty and info passes are inconsistent. The way it is designed, the render layers should have precedence over opacity. What the info pass does is the correct behavior. We will fix this for the next release.

cheers,
Thomas

[caffe3]

English is not my first language, so bear with me please

So, for now the workaround is to render the scene one time with Render Layer enabled, to get a Main/Beauty pass + Shadows pass and then afterwards re-render the scene a second time, although with Render Layer disabled, to get Info passes (like AO) and Mattes (Layer Masks).

And in the future when Render Layers gets fixed, we will be able to render one time with it and get a Main/Beauty pass + Info passes where objects with opacity is not completely deleting/clipping objects behind it (that looks like Main/Beauty pass instead)? As for isolating individual objects to color correct in post, the mattes (layer masks) are not really needed if the Object ID's/Material ID's passes work as they should, which brings me to my last question...

Is there a reason why we can't manually set the color of Object ID's/Material ID's ourselves? Like, there should really be a color setting in each material to specify the Material ID color the material has, and a color setting in each Object Tag to specify what Object ID color the object should have. If not, I'm wondering what use the Object and Material ID's really have if you don't have control over them.

[stratified]

Hi,

Yes, you would need to render the scene twice. Luckily, the info passes are pretty fast.

When the bug is fixed, the beauty pass should be clipped as well. The render layer is a property of the geometry and should work the same regardless the material applied. What are you trying to achieve? Usually, you don't set up a scene with a wall blocking the geometry on the active layer.

Originally, the material ID and object ID were just tools for us to debug. We only made the info channels "public" later. Some users use them for masking but when we wrote them we didn't have that in mind They are extremely limited and require more work to make them configurable. Making them configurable isn't high on our priority list.

cheers,
Thomas