[bjorn.syse]

Hi

I'm rendering a bottle with a coloroued liquid and having trouble defining the right workflow to create a free cut image with transparency. I've come across the following problems that I would love some help with troubleshooting:

1. When rendering without the regular alpha, but only a custom alpha channel - that custom alpha channel always comes out as opaque whether or not I've checked the opaque flag. Is this a bug?
2. my second problem is, I would like to cut out the semi-transparent parts of the png, and when using the proposed workflow in the manual, the last step, Remove black matte really cuts the entire color our of the fluid. Therefor, if possible I was aiming to render a custom alpha because by avoiding to render the regular alpha I can get an output render without a premultiplied background and get around the "remove black matte" problem.

Best regards

- Björn

[bjorn.syse]

Hi again

I'd like to clarify myself somewhat,. What I'm after is basicly to render a bottle with a liquid, on a white background with cut out alpha/transparent and semi-transparent parts, but then have a reflection underneath. Right now I have these problems which interconnected, but let's start with this one:

1. When using the embedded or separate alpha, I have problem with "remove black matte" in photoshop. It seems it removed too much of my object, not only the black fringe. Have a look here. First image before black matte, second after.

Is this a problem with the gamma? Image being 8 bit? or what's going on here?




Regards

- Björn

[MartinBrinks]

Hi Björn

Intrigued by your questions to look a bit more at the alpha channel I did notice they mention a PS action available that handles the entire process. Did you try that one?

[bjorn.syse]

I did, yes. It produces the same results..

[tom]

Could you please share the unprocessed render and alpha channels?

[bjorn.syse]

Hi Tom, thanks for having a look.

Here is a link for the entire scene and renders, this one including a regular alpha pass:
https://www.dropbox.com/sh/hbv95lvgx8k0 ... jF7Ca?dl=0

And here is another render omitting the regular alpha pass:
https://www.dropbox.com/sh/oc62xu0zqkj3 ... GflVa?dl=0

In the first one, try opening the render png (with embedded alpha) and do the Remove black matte trick. It seems to me that it deles a large part of the bottle and liquid aswell.
In the latter one, I'm surprised both of the custom alphas come out as opaque, even though only one of them have that flag set.

What I'd like to achieve in the end is a free cut image with non-opaque transparency, and the reflection on a separate layer in photoshop. Not sure which way is the best towards this.

Regards

- Björn

[tom]

Björn, Remove Black Matte is designed for removing the blackness remaining in the beauty passes which are only rendered against pure black background. Therefore, it cannot work this way properly. Actually, rendering clear objects against a transparent canvas has always been hard. Amount of reflections and the luminance of background color should be very well adjusted. Lately, I have spent a few weeks making test renders for a similar project and it was not really easy at all. I'd suggest you rendering it on a light or light grey background as you did and removing the alpha without applying remove black matte. Because, you know there is no black matte in it when you render it against a non-black background.

[bjorn.syse]

Hi again,

Thanks for your answer. But, then two questions arise:

1. How can I render it agains a grey background, since whenever I choose to also render an alpha channel, the background automatically turns black - right?

2 (related to 1),. In theory, I could perhaps use the Custom alpha pass. But if I render the custom alpha pass without the regular one, it comes out as opaque whether or not I've checked that flag. Is this correct?

Regards

- Björn

[tom]

You summarized it very well and for this reason I've also rendered these channels apart. I understand it's taking double-time but, there is no other way I know.

[bjorn.syse]

I see.

What's the reason for the Custom alpha not bein transparent in lack of a regular alpha?

Regards

- Björn

[tom]

You're right and I see no reason for it. I guess we can evaluate implementing transparent custom alphas it in the future version. But, after a lot of requests so far I started to think we also need a [x] Render Against Black option instead of forcing it. I will keep this case in mind and we will consider what could be done. Thanks for the input!

[bjorn.syse]

Ok, cool.

But as you allready know, there is allready an option whether or not to make the custom alpha transparent or opaque - the problem is it only works when the regular alpha is in effect. Therefor in the current implementation it seems more like a bug.

Thanks for the clarification though!

Regards

- Björn

[bjorn.syse]

Speaking of this, after upgrading to 3.2. This is my custom alpha:

[tom]

Could you please send me the environment map? It's missing and ends up with a different look. Also you are not using nested dielectrics feature. Is your liquid intesecting the bottle thickness?

[bjorn.syse]

Now I've put it in those dropbox-folder i shared earlier.

However, now I've also updated these files to use Nested dielectrics intersecting volumes and priorities. (Bottle has prio 0, decal prio 1, Liquid prio 2 and that tube in the middle has prio 1). Here is a new folder with this project:

The PSD is the render with channels. (Love how you can export a PSD now!)

https://www.dropbox.com/sh/j70rhfoo2lxt ... 9UO6a?dl=0

(If you for some reason run Cinema 4d R17, i could also put the original file in there)