Cryptomatte caused massive cost to render time.

[stezza]

Hi folks.

I had to stop my rendering due to massive cost for such a simple logo, 360 rotate.

I had sent 125 frames png sequence to render, @1024x512.px.
On my local machine each frame took 24sec to complete of a single black colour, spinning logo, with alpha BG.
I noticed that the credits spent was 47.7 and was only half way rendering so I cancelled it.

Surely the time to render the 125 frames should have been around 1-2mins max when each frame took 24 sec on my not very powerful PC.

I downloaded the zip files and noticed that the 125 frames plus cryptomatte would have been 250 files but there was 750 frames in the download zip and thats not including the jpg preview files.
The logo did render but there were 3 extra sets of cryptomatte sequences with no colour data present in the files.

If you could take a look and see what went wrong.
Company: Torpdo_Group
Scene file attached.

Many thanks
Steve

[vladie]

Hi Steve,

I asked my colleague - the PM for V-Ray for Maya to help. We had a look at the scene and nothing seems to be out of the ordinary, everything seems to be as expected.

However, there are things in your setup that are worth mentioning:
*) You're using cryptomatte with PNG output
--> Cryptomatte only works with EXR output. Other formats don't encode meaningful data that Cryptomatte plugins can use in other applications like Photoshop, Nuke or Fusion.
--> When using Cryptomatte, there are a number of additional channels (render elements) generated. There's one 'preview' channel that holds simple mask previews. The rest of the channels hold the actual cryptomatte data. In the VFB, only the preview channel is visible for convenience, while the rest of the additional cryptomatte channels are hidden. However, when writing the output images, all channels are written.
--> This explains the additional image files you're seeing. Outputting the additional channels does not add up to the render time, though.

Question: Is there a specific reason why you're using cryptomatte with PNG?

*) You're using the Blinn BRDF type of VRayMtl.
--> The default GGX is generally faster than Blinn. GGX can better represent a wide range of materials and if there's no specific reason to use Blinn, I would recommend using the defaults.

Bests,
Vladie

[francomanko]

i just got caught out with the png output and no cryptomatte...rendering in the cloud just produces black or empty matte images.

Question: Is there a specific reason why you're using cryptomatte with PNG?

I have to kind of turn the question back, would it not be possible, if you can see the cryptomatte in the VFB, you cant have it exported when using png, so what you see in the VFB is what you get, in cloud. I understand what you said about the exr having the extra data, but i dont need that, I render in 16bit PNG, i just need the same matte representation I get in the vfb, to be rendered when i send to the cloud.

[yolov]

What you see in the VFB is the cryptomatte 'preview' channel.
The Cryptomatte output requires a MultiChannel EXR file by specification, as the actual cryptomatte data is encoded as metadata in the file. The preview itself is not the actually cryptomatte masks and it doesn't get saved with the output, as it can't really be used for anything. The cloud simply outputs the same files you'll get locally for PNG output, nothing more.
Cryptomatte has a plugin for Digital Fusion and Nuke. Recently, there's EXRIO that is able to read the cryptomatte data from EXR files and construct the masks for Photoshop, so that's another way to use it.

I hope that helps.

[Neilg]

, i just need the same matte representation I get in the vfb, to be rendered when i send to the cloud.

So how do you use this in a sequence? What are you doing post production in, and how have you been getting selections?

[francomanko]

Sorry i didnt mean to hijack this thread. Im not using in it an animation, im using it for stills, in photoshop as a quicker, albeit dirtier way of avoiding setting up multiply 'multimattes' .

I get that im not using it for what its designed for. but my point is that you never know what things might be used for, if i can see it in the vfb, then, as long as its not too hard to do, ideally it should be outputted in the cloud render as well...like for like.

[yolov]

Okay, thanks for making it all clear.
Like mentioned above - the cloud simply outputs what V-Ray outputs, so this is on the V-Ray side.
We'll run some internal discussions here and as far as I understand, simply enabling an output for the preview channel will enable you to keep your workflow (with a note that the masks aren't actually proper masks in that preview channel), is that correct?