in mantra , why there's no option to render just the alpha channel only or deep raster channel only.

…hmm…. because channel managment in mantra is driven complitely by artbitrary user decision? So it's up to you which render variable you want to store in which channel… is this good answer? channel's names is only convention: rgba pz P Of etc.

So what stops you to pipe-in under VOPs so called “deep raster data” into rgb channel?

The name for this is flexibility. The price for this is that you don't have handy buttom to render only that or that. Still during shader dev. you dacide what mantra renders.


cheers!
SY.

thanx,

but still don't know how to render the alpha channel only,
i tried to render Af variable to C, but does'nt work.

Why is it so necessary to only render the alpha channel? is it disk space?
If you just make the Cf channel black then you will still get an Alpha but the file size won't be much different to just having a single channel.

You partly right! It seams to me that mantra/Houdini expects first plate to be 4channel plate. Then, other plates are whatever you want. Files from deepraster Tab are complitely arbitral on the other hand. First plate can be floating point one channel data for example.

But still you can put in your alpha to rgb just after convering it from foat to vector… for me it works like a charm. With lzw compression under tiffs, it's vary small even keeping in three channels the same data. You can output alpha to “r” and leave “gb” black to make it even smaller, if you really need it .

…or make emply shader to render black plate and use deepraster to output alpha as one channel single plate…

…or in your own shader override Cf variable to be float not vector, put in it alpha and export it. Not sure if this is possible, just can't check now…

O! no! plenty posibilites! I'm loosing my mind!


cheers,
SY.

actually not about disk space,
i've render the complete scene with all the ‘expensive’ shader.
but not happy with the result etc.
now i want to render alpha per object so then i can recomposite,
then use/input this as mask in compositing.
i don't want to re render the whole thing which will take very long.

anyway i found it already,
in deep raster, set variable P/Af then output to some flat image format.

thanx.