How do I render a material ID pass?

[DPS]

I've tried two objects and also a single object with two different material IDs, and no cigar.

[flino2004]

There is many ways to do it... But out of the box in vray ( I'm not in front of my computer right now) if I remember well is vrayelementsid or something like that.... You will get 3 materials per element in RGB colors.... Select the color that you want and change the ID. I usually have already in my workflow all the 15 numbers besides zero.

Remember to rename your render elements or you will override them.

Fernando

[DPS]

Thanks for the reply - I had forgotten that this material ID was independent from the Face material IDs. Is that the only way to do this? One material ID per node in the material editor as you choosing? This is fine, I'm just trying to learn the different possibilities.

And why did you mention "3 materials per element in RGB colours"? Is there an advantage to this? If you use all of the available 15, it picks colours/shades randomly as far as I can tell.

As you can probably tell I'm pretty fresh to rendering elements/compositing - I've done some really basic ones but feel this is an important string to add to the bow!

[Dariusz Makowski (Dadal)]

What he mean by 3 materials per element is that 1 render pass Multi Matte(or what its called) has 3 colours to it: R G B. The Red Green and Blue are primary colors there fore in photoshop you can pick them up from channels RGB. So since there is only 3 primary RGB you can have only 3 different masks in 1 render pass. So if you have 7 materials that you want your ID for then you need 3 Multi Matte passes.

1 pass with ID 1 - 2 - 3
2 pass wind ID 4 - 5 - 6
3 pass with ID 7 - x - x

I put x because you dont have 8 and 9 material so they will be just blank.

Hope this helps.

[DPS]

I take it then that magic wand wont cut it if using more than three? Hence just using three mattes per element?

I understand that they would share RGB values.

[flino2004]

If you save your rendering using Exr format you will see your elements in layers...so let's say wood has Id 1 and it's red and metal1 is ID 4 and it's red as well, but they are in different layers, so now you select them independently because you have the masks to do that.

[DPS]

Sure - but if you used more than three material IDs, wouldn't selecting the colour variations with a magic wand do the trick?

Sorry if I'm misunderstanding things.

From you reply I'm wondering if there's a way to choose what colour your IDs are? Isaw this vray feature when I did a google search but it wasn't within 3DS Max.

[DPS]

I just tried this - and I see the problem. Thanks for the replies.

Edit - I missed the MultiMatteelement suggestion on first read - this is good stuff.

[Dariusz Makowski (Dadal)]

You DO NOT use magic wand to select ur channels!

You go to channels in photoshop and either duplicate each channel and then press CTRL+Click on duplicated channel to select mask. Or just ctrl+Click on channel you want to select.

Dont use magic wand you will have more edge problems.

[DPS]

You DO NOT use magic wand to select ur channels!

You go to channels in photoshop and either duplicate each channel and then press CTRL+Click on duplicated channel to select mask. Or just ctrl+Click on channel you want to select.

Dont use magic wand you will have more edge problems.

Check.

*customises UI and hits delete on magic wand*