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I'm using one of HDRI from http://www.hdrlabs.com/sibl/archive.html. I would like to blend/merge it with scene but in a way that the HDRI content is not visible only dimmed and blurred. How to achieve that but in a way that the lighting is perserved?

vejn
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Set your HDRi images to light your scene as you'd normally would.

Enable Environment in the light passes section of the Layer Properties.

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Enable Film Transparent, so that the background will render as an alpha channel and not as the world backgrund:

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In the compositor use the output from the environment and blur it and darken it at will, then combine that result with your scene using an alpha over node.

That way the illumination for the scene will remain intact and the Background can be affected independently:

enter image description here

HDRi by GiantCowFilms

UPDATE: read this link to prevent a darker edge around the objects

(Images for version 2.7x)

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susu
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  • I am trying your technique, but in the results that I get, a dark edge (like a dropshadow) appears between the 3D objects and the HDRI background: http://imgur.com/a/VRBjC – MicroMachine Aug 29 '17 at 17:37
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    @MicroMachine. New questions should be asked in a different post. Use the Ask Question link at the top of the page. In your question you can then add a link to this question as refference. –  Aug 29 '17 at 17:39
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Blurring the HDR image used as environment, can be done by manipulating the texture coordinates:

enter image description here

Note that you might need to change the strength used for the environment.

(for info on how this works please watch Bartel Skorupa's video Manipulate texture coordinates like a boss)

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To soften/blur the HDRi use Photoshop or Gimp to blur the image (I suggest making a copy of the original ).

To control the intensity in the "Node Editor" select the "World" nodes (Attached is the most common set up I use).

Adjust the strength in the "Background" node (2).

As a side note you can adjust the rotation of the HDRi which affects the position of the light source in the "Z" rotation of the "Mapping" node (3).

Dontwalk
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    If I blur it in Gimp, wouldn't I loose it .hdr properties? I would like to have full lighting only that it can't be seen. – vejn Mar 04 '16 at 21:29
  • It would depend on the amount of blur. I've blurred them in the past to soften reflections in shiny materials. Worked great for me. I would suggest starting with a slight blur and see what it looks like. Add blur to taste. (Save the original as a back up and for future use). If you don't to see the HDRi in the final render check off the "Transparent" check box in the "Film" section of the Render Settings. – Dontwalk Mar 04 '16 at 21:59
  • Btw, how come there isn't blur node in world tag ? – vejn Mar 04 '16 at 23:08
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    Loading an HDRi in gimp will convert it into an 8 bit image. You'll for sure loose all of the advantages of High Dynamic Range. Upcoming versions of Gimp (2.9 or higher) will be able to deal with higher bit depth images. –  Mar 05 '16 at 08:07
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    @cegaton Except GIMP, much like the anachronistic leader it models itself in its image from, is strictly display referred. So, even with a deeper bit depth, correct wide dynamic range handling will still elude it. – troy_s Mar 06 '16 at 04:29
  • @Gimp... I use Photoshop. But Gimp is free. So, it's a not so perfect, perfect, alternative for people to use/experiment/learn with. – Dontwalk Mar 06 '16 at 04:55