Hi,
I am trying to implement an id pass.
Ids are kind of working except the ids show different random numbers for some reason.I have attached the file.Please have a look and correct me.thank you

I'm a little confused what you mean here. When I first render you're file I get a grey grid with a white teapot on top of it. Looking at the values on the material shops assigned to the objects, this is what is to be expected.

Personally for an id pass I would set the opacity on both materials to 1 and change the colour values to red(1,0,0), green(0,1,0) or blue(0,0,1) for different objects, instead of changing the opacity as you have done here.

badhairday
I'm a little confused what you mean here. When I first render you're file I get a grey grid with a white teapot on top of it. Looking at the values on the material shops assigned to the objects, this is what is to be expected.

Personally for an id pass I would set the opacity on both materials to 1 and change the colour values to red(1,0,0), green(0,1,0) or blue(0,0,1) for different objects, instead of changing the opacity as you have done here.

as far as I know idpass is used to key out any objs in the comp.
if you right click in mantra ip and click on inspect you can see that grid,the teapot might have a random id in my case.my doubt is why I am getting the random ids and how to get a properly arranged numbers

you mean,you will assign different constant shaders each of different rgb colors to different objects?I think I did not change opacity.I just entered few attributes in the mantra in the image planes.
can you please share a sample file so that I can still understand what you mean?

Sorry, I didn't even notice the render plane on the mantra node, I thought that you were trying to put the id pass into the colour image plane.

Anyway, to try to save more confusion, I've taken you're file and have modified it slightly to demonstrate how I would do an id pass. Here are the things to look out for in my file:
You'll notice that both the grid and the teapot now have the same material applied to them (this doesn't have to be the case by the way, but I've done it for simplicity here). Inside the grid and the teapot I have created a vector attribute called id. This vector value represents that objects value in the id pass. If you look inside the constant shop node you'll see a yellow netbox which is where I make the shader pick up the id attribute I created at sop level. Then if you look at the mantra node, I pass the attribute coming out of the shader in as the image plane's vex variable attribute. If you render the mantra node you should see a red teapot and a green grid in the idPass image plane. You can then take this into the compositor of your choice and use the red channel or the green channel of this id pass as a mask.

hi,i seen your file! but this is more like a matte pass.what do you think? i mean its use serves the same as id pass.but this is not an actual id pass.i dont see any numbers or ids in the mantra ip

badhairday,

That scene along with your explnation was very insightful, but I do not find it very practical when you start to have a scene with many objects in it. So instead of having to create an attribute inside each and every geometry with the desired id color, it would be much more convient if you could instead adjust the id colors acording to the shader that the given geometry is using.

For others out there who wants to do id's pr shader, just go into your SOP level in your given shader and add a parameter. Name it idpass, name : idpass, Label: idpass. Type:Vecto (tyoe in your desired color in the Vector Defaults. Export: Always.

Now in your mantra output node, do as badhairday described and you will not have an idpass working.