Render pass 101

[N-drju]

Hannes' last image and his mention of render pass of the luminosity made me realize that... I don't really know much about render passes.

One thing I am sure of is that this is a technique of rendering various parts or effects in the image separately.

Unfortunately, I don't understand what is the benefit of using this method. Judging from Hannes' image, it might be useful to have some of the image's elements more pronounced, deeper. 

However, is it really beneficial to use a pass workflow in still images? Or is it somehing that is of more use in movies? Isn't it just better to render all image elements at once?

[KlausK]

Hi, let me try:

Control. Control over every aspect and element of the final image.
The possibility to simply re-render one or two elements to change them.
No need to render the whole image again. So, much faster turnaround in specific situations.

Sure, it might be more of a hassle to set it up for a still image at first.
But think of a Photoshop image you want to create. I don`t think anyone would attempt to do it all in one layer.

And "better"? No, the outcome of the final image would be exactely the same wether you render it in one or many passes/elements
and composite them together without altering the singele passes in any way.

If I were doing more complex scenes with imported objects e.g. I surely would go the render passes route.
If I were attempting to produce images as a professional I would be sure to get the render passes workflow in my arsenal.

Take the time and watch a few videos about render pass compositing.
That would be my advice.

CHeers, Klaus

[N-drju]

But think of a Photoshop image you want to create. I don`t think anyone would attempt to do it all in one layer.

Good point. I haven't thought of this comparison.

I think the Creative version does not have the layering component though, so it's more like a theoretical education for me now.

But to take your information into account, it seems that the elements rendered in a pass should then, generally, be the ones which render longest. Does it sound right?

[WAS]

But think of a Photoshop image you want to create. I don`t think anyone would attempt to do it all in one layer.

Hey! I was new to Photoshop once! Lol. I remember forgetting and painting on layers a lot lol

[Hannes]

But think of a Photoshop image you want to create. I don`t think anyone would attempt to do it all in one layer.

That's it! I usually try to make an image as good as possible as it is, but sometimes you may want to change things afterwards without having to rerender the whole thing.

[KlausK]

But to take your information into account, it seems that the elements rendered in a pass should then, generally, be the ones which render longest. Does it sound right?

Yes and no, in a way...I`d say.


You have to distinguish two terms here: Render Layers and Render Elements.

First, you have a Render Layer.
This layer can hold all kind of Render Elements. These are the "extra output images" in TG.Pro.
It can hold different sets of Lights or Objects, for example. I think you can have 5 Object and/or 5 Light Groups
with any number of lights and objects. So you could have five different setups of lighting for a scene
rendered out in one go - without the need to have different projects being loaded up one after the other
and applying the changes to each and every one.

You are able to create more then one Render Layer in a scene and have different outputs rendered at the same time.
Which light influences which surface, which object is visible or not, cast shadows etc.
You could use a Render Layer to override Global Illumination in a scene.
A very common use for Render Layers is to render out a Z-Depth pass to be able to change the Depth-of-Field afterwards, for example.
Very helpful might be to separate Clouds and Atmosphere from the rest of the image.
And re-use it in another - completely different - scene in a compositing program.
You can render out all the Alpha-channels for the different Elements.

It adds up to render time for sure, how much it adds up I couldn`t say.
But it might be worth it in the long run.

Here are links to the Terragen Wiki:

https://planetside.co.uk/wiki/index.php?title=Render_Layers_and_Render_Elements
https://planetside.co.uk/wiki/index.php?title=Compositing_Terragen_Render_Elements

Maybe take a look at them. You can find all I said here and much more.
Not too much to read but the TG specialities are explaind well (much better then I did ) and illustrated with examples.

CHeers, Klaus

[digitalguru]

I did some tutorials on this (7 years ago now!) for Render Elements -- shows a few tricks you can try.

https://www.youtube.com/watch?v=ihY_kp2rzxg
https://www.youtube.com/watch?v=vS21UjyQpWU
and a Photoshop based tut:
https://www.youtube.com/watch?v=LNv9iEdv4k4