Aliasing Info Coverage pass

[Jolbertoquini]

Hi Guys,

Just a quick question I have made a script for nuke to work with ID, In my old workflow I was using mentalray and I generate a ID pass and Coverage Pass and this script was create a alpha.
Now at my new workflow with Octane the ID is quite hard to make work because of the aliasing and before with the coverage pass was help me to create that aliasing info now I'm stuck I can get the alpha but without aliasing please have a look at the attach example of the mentalray renders with ID (no aliasing) and coverage pass (aliasing information).

with this two I can separate the color value and multiply with coverage to get a clean alpha.

Cheers
JO

[stratified]

I've replied here but let's discuss in this thread.

Hi,

Octane is a ray tracer and traces multiple rays per pixel, as a consequence, all edges will be anti-aliased. You can make the edges sharper by decreasing the filter size in the kernel node but you will still have smooth edges. If you take less samples per pixel, you will only get jagged edges and it will look weird.

I don't understand what you are trying to do. The picture on the right doesn't look like an alpha mask to me. It has the outlines of each objects but how would you use this? You can render proper alpha masks of each individual object via the render layers. Or you can use the render layers to render each isolated object and you don't need an alpha mask.

cheers,
Thomas

[Jolbertoquini]

I've replied here but let's discuss in this thread.

Hi,

Octane is a ray tracer and traces multiple rays per pixel, as a consequence, all edges will be anti-aliased. You can make the edges sharper by decreasing the filter size in the kernel node but you will still have smooth edges. If you take less samples per pixel, you will only get jagged edges and it will look weird.

I don't understand what you are trying to do. The picture on the right doesn't look like an alpha mask to me. It has the outlines of each objects but how would you use this? You can render proper alpha masks of each individual object via the render layers. Or you can use the render layers to render each isolated object and you don't need an alpha mask.

cheers,
Thomas

Hi Guys, I had some issues for videos basically as said before we use Nuke for composting the problem of the ID we have now we can separate the alphas in a perfect way (I tried many different always photoshop does but not perfect)

We use a old techniques used for many year at the industry like Coverage pass (many people stop using to create so many passes I don't know why?)
here a example of this method http://www.sigillarium.com/blog/lang/en/379/

So we use Mental ray to generate this two passes one with flat color to be easier to select and have perfect selection and then we multiply with the coverage to add the aliazing information. We still use Mentalray because we have automatic scripts on Nuke were we clic at the object and nuke generate the alpha for it quite faster and easier.

My point is the ID provide with Octane is focus to use magic wand with tolerance settings each is not excellent alpha.

[Jolbertoquini]

Also one other major problem we find with the ID is about texts overlay some case the alpha texture add at opacity on the shader is not recognize by the ID pass specially when we use double side polygon to show 0 opacity one side and the other the texture alpha. Id still render the all mesh. and material ID also doesn't work.

[stratified]

Hi Jo,

Mental ray is a scanline based so it's probably a lot easier to disable anti-aliasing. Like I already explained, because we take multiple samples per pixel, Octane always does anti-aliasing. You can get aliased edges by simply rendering only a few samples per pixel. You can use this to generate a coverage pass yourself in Nuke as explained here. I still think it's a crappy solution.

coverage_pass.png

You can generate nicer alpha masks from Octane or even better, you can render parts of the beauty pass in isolation.

logo_mask.png

logo.png

The Octane and Nuke projects are attached in the zip file.

coverage-pass.zip

cheers,
Thomas

[Jolbertoquini]

Hi Jo,

Mental ray is a scanline based so it's probably a lot easier to disable anti-aliasing. Like I already explained, because we take multiple samples per pixel, Octane always does anti-aliasing. You can get aliased edges by simply rendering only a few samples per pixel. You can use this to generate a coverage pass yourself in Nuke as explained here. I still think it's a crappy solution.

coverage_pass.png

You can generate nicer alpha masks from Octane or even better, you can render parts of the beauty pass in isolation.

logo_mask.png

logo.png

The Octane and Nuke projects are attached in the zip file.

coverage-pass.zip

cheers,
Thomas

Hi Thomas,

Thank you for the examples, one thing I can't open your Nuke script seams a wrong format could you post the python of the node so I paste on my nuke Please.
Yes, I get also weird results...if I have 1 sample I get weird spots and if I add the 4 samples still sampling little bit, so is possible to have a render of two ID in the same time on batch option? Also one other question what the best solution to make work alpha textures appear on the ID material when we use shader mix or Polygon side texture?

Cheers
JO

[Jolbertoquini]

Also, I did a lot of test but still not working well as you mentioned, the good for this type of passes we can render one go only two passes to have all alphas we need on comp and save size of file renders. for some scene where we have a lot of shaders render separate is always complicate.

Yes but I understand also about the way Octane samples. and the difference technique is not the best in Octane this case as you said we still Use Mentalray on pipe line for that but we would like to have all in one job at Octane only. for the future VR rendering (camera and other extra things) .Again is not a big problem for us because we have script which generate all on the background so we just convert Octane scenes, as I said would like have work in Octane straight of the box (also I understand the reason)

Thanks for all help Thomas

JO