Alpha Channel + Transparent Materials for Compositing

[blackwater_hollow]

Hello everybody!

I have a quick questions about using alpha channels with transparent materials (plastic) in Octane.

What I am trying to achieve is rendering out a clear plastic object in Octane with 'alphachannel' turned on, saving the render as a transparent PNG image, and then using Photoshop to place a background image behind the clear plastic object so that the background image can be seen through the clear plastic object.

I have tried to find a solution to this problem, but have not been able to find any documentation.

Any suggestions, pointers, links, or advice would be greatly appreciated!

Thanks again!

[FooZe]

Hi blackwater_hollow,

There are a couple of way of doing this depending on what you are trying to do.
One way is to set the opacity to less than one for the material you are looking through.
This will only really work if you are using some kind of glass and you are not concerned about the index of refraction.

The other way is to use your background image for the environment texture in octane. You may be able to get away with tweaking the scale and location (depending on your scene) or if this is obviously distorted or tiled, then you will need to somehow either covert or composite your background into an HDR environment map. I'm not sure how you could do this, most likely you would need some tool, and also there is the question of what else to fill the full map with (ie: what is to be displayed behind you?). Obviously this will also effect the lighting of the scene too, so depending on your scene it may or may not be feasible.

Thanks
Chris.

[blackwater_hollow]

Hi Chris,

Thanks for the quick response!

In the past, when I used cinema 4d for rendering, I would use an 'object buffer' tag on the transparent object, and alpha channels on when rendering to a PSD image file. Then, when I imported the file into photoshop, I would be able to select the outline of he object that was 'buffered' in the channels menu, and the alpha channel selection for that object would be feathered, allowing the underneath layers to show through the transparent areas that where not affected by a strong reflection or refraction.

Does octane have a similar function such as 'object buffer' for easy photoshop single object alpha layer selection?

Thanks!

[FooZe]

Hi,

Short answer is no. The closest would be option 1 in my previous post, make the objects material partially transparent with the opacity setting. For realism, this is never going to be very good. To have proper visibility of the background, effected correctly by the index of refraction on it's way through your material, the background needs to be added in octane so it can be sampled in the scene.

Thanks
Chris.

[blackwater_hollow]

Hey Chris,

Thanks again for you response!

As you suggested for option 2, is there a possible way in Octane to have alpha layer selections for specific objects assigned to certain materials? As mentioned before, C4D had this option with 'object buffer'. I mention this because I am curious if it would be possible to place a plane behind the object I am rendering from (included in the obj, exported from c4d), and putting the texture of the background on it, and then once rendered, just cut out the object from the background plane?

I tried option 1 that you had suggested, but sadly the image map took image and wrapped it around the environment, giving me a real nasty overblown lighting condition. If I decrease the power on the image, the background becomes grey rather than the cloud white I need, and really makes things difficult.

Thanks again, Chris!

-Conrad

[abstrax]

I'm not sure what you want to achieve, but you can render the image with an alpha channel and do the compositing in Gimp, Photoshop or C4D onto whatever background you want. There is no concept of an object ID in Octane and it's currently not designed for compositing. There are other tools for that.

Cheers,
Marcus

[kavorka]

I have ran through this kind of problem myself. My solution was to use the image I wanted to make transparent as an alpha mask in Photoshop. It needed a bit of modification, but it worked fairly well. This will only really work with a solid background behind the transparent object (if you can make it black, even better). I also used my modeling program (blender) to render out a couple alpha channels of other objects in the scene and composited those together with my image I wanted to make transparent so I could control what becomes transparent and what doesn't.

Depending on the complexity of the object you want transparent, this may not work, but in some cases, it will give you a nice effect.