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How could I render part of my image at a higher amount of samples then the rest in Blender using Cycles Renderer?

What I want to do is render a certain portion of the image at a higher amount of samples (400) than the rest of the image (200). Is this possible in blender?

I know that there are multiple questions regarding only rendering one square of the image, however I am not sure how to render the border only?

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  • 2
    $\begingroup$ In camera view press Ctrl+B and drag your cursor to define the portion, which will be rendered. $\endgroup$ – Paul Gonet Oct 24 '15 at 21:56
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There are two ways to do this.

1. Two Pass Render and Combine
One way is to render the whole image at 200 and then render just the selected area using border render to render the 400 sample area, and then combine them with the compositor or an image editor.

Pros: Good for small areas of an object, or large swaths of the scene involving multiple objects. Cons: requires extra rendering to a small degree.

enter image description here



2. Use Render Layers to Set Different Sample Levels
The second solution, which would allow you to do it in one task would be to use render layers. If the objects that require 400 samples can be separated onto a different render layer than the rest of the scene, you can set a different sample amount per render layer.

Pros: Gives you more fine-tuned control over sample levels on an object level. Not limited to rectangular selections. Cons: Can't render different portions of one object with different sample levels.

enter image description here



2b. Advanced Example
Here is an answer that extends the render layer answer above. It is more specific to your blend file and allows the rendering of the text and text shadows at the higher resolution.

The main idea is to separate all the items plus a shadow catcher plane across 4 render layers. This way you can set the sample amount for each layer.

Here's the final comp plus the separate rendered layers:

enter image description here

Here's the Render Layer set up:

enter image description here

Note that the Background layer is excluding the other 3 layers, and the ShadowCatcher layer excluding the Background layer.

Here's the composite node tree to combine the layers. Please note that I used the Shadow pass of the shadow plane, not the combined layer.

enter image description here

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  • $\begingroup$ These are exceedingly good answers, however the cons on both restrict me from using any of these for my current scene. Though I may use this wonderful technique on other blends, I need to find a way to do this on one object, without rendering more than I need to, which is the goal here. Is there a way to use method #1 to just render the borders? $\endgroup$ – Rubyjunk Oct 25 '15 at 14:00
  • $\begingroup$ I'd be happy to tailor the answer more directly to your scene. However, I need more info about what you are trying to do in order to provide a better answer. Can you describe your scene more directly or post the blend file? $\endgroup$ – Todd McIntosh Oct 25 '15 at 20:31
  • $\begingroup$ Sure. Here it is --> drive.google.com/file/d/0B6D6o6-MSCMgZWRsZ29KVWhuY00/…. I want the text at higher samples than the texture. However, I want the part of the texture that has shadows and stuff on it to be rendered at higher samples as well. $\endgroup$ – Rubyjunk Oct 25 '15 at 21:09
  • $\begingroup$ What if you could render the text shadows on a separate render layer and composite it back on to the main texture plane. Would that be good enough? $\endgroup$ – Todd McIntosh Oct 25 '15 at 23:43
  • $\begingroup$ What I would do would be to separate everything on to 4 render layers. Your main plane would be on a background render layer at 200 samples. Then you would add a plane to catch the text shadows on a second render layer with 400 samples. Then your text layer at 400 samples, and then your foreground elements at 200 samples. Your shadow plane could be pure white material, or you could enable the shadow pass on it. The only tricky thing is excluding it from the main plane layer so it doesn't block light or affect the main plane. Then comp the four rendered layers together. $\endgroup$ – Todd McIntosh Oct 25 '15 at 23:49

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