Volumetrics in Gimp

[evil_genius_180]

First of all, many thanks to limdeapl for his great Photoshop sunbeam tutorial.

Basically, I wanted to cheat at volumetrics using the free software GIMP, so I modified limdeapl's tutorial, as GIMP has slightly different tools than Photoshop but you can achieve basically the same result.

First, start off with an image with a single bright spot, ie: a sun. In this case, I made a quick background in GIMP with some plasma, a little color change and a flare. Then I rendered a Superman shield against the background.



The first thing you want to do with your image in GIMP is to go under the Layer menu and select Duplicate Layer. This will give you 2 layers that look like your image.

The next step is to go under the Filters menu, Blur submenu and select Motion Blur. You'll get a little box that looks something like this:



Next, click on the little circle next to Zoom and set the center of your Zoom at the center of your sun. Check the Preview box and set the Blur Parameters Length slider to whatever you want.



Click OK and it will blur your duplicated layer.



Now, for some reason, when you blend in GIMP, you need to have 3 layers. So, you can create a new transparent layer by clicking on the Layer menu New Layer tool and clicking OK without changing anything. Or, if you want a heavier look to your volumetrics, simply duplicate your blurred layer. (that's what I did for my example to make it more interesting.)

Next, go under Script Fu menu, Animators submenu and select Blend. Set the options on the blend tool box at whatever you want and click OK. This is the result.



You can also tweak your final image. For me, an image isn't an image without screwing around with the brightness/contrast tool under the Tools menu, Color submenu. I did brightness -40%, contrast + 40% to get this.

[Ozylot]

Neat stuff! im gonna have to try gimp someday.

[evil_genius_180]

Thanks. It really is a sweet program for those who can't afford pricey software.

[B.J.]

So, why did you use Blend? I got a similar result just by making the blurred layer semi-transparent.

Also, does anyone know if there's a plug-in replacement for GIMP's awful Zoom Blur? If you'll notice in evil_genius' 4th image, the Zoom Blur is not smooth at all and looks like a stuttered zoom. It's not too bad for pictures like this, but it's horrible for pictures with small features like starfields.

[Helot]

^ B.J. do you have 2.2? Supposedly some fixes were made to Blur.

Neat tutorial from a neat tutorial!

[B.J.]

I'm currently using 2.2.15. They're up to 2.2.17 on the stable releases, but I didn't see any blur fixes in the logs. Since I can't compile, I'm not touching the development versions (2.3.X) until they release 2.4.

[Taranis]

Excellent tut EG180 ... It nice to have 2 tuts on the same subject using different Programs

[evil_genius_180]

Originally Posted by B.J.

So, why did you use Blend? I got a similar result just by making the blurred layer semi-transparent.

Similar, but not the same. It's a bit different when you blend it than when you make it semitransparent. The non-blurred s-shield wouldn't show up as well if I'd done it semi-transparent as it does when I blend. I've tested both ways many times doing various projects with blended layers.

As far as "is this the only way? Probably not. I'm sure there are others. Maybe even better ways. As I said, I was adapting a Photoshop tutorial and it works pretty well so I figured I'd share with people that don't know how to do it. I agree that the zoom could be better but that's what it's got.