Artistic Glow is an effect that is a component of almost every major photo editing software package. Blender has the ability to recreate this effect, but with more control and more finesse, because of the unique node based system in which glow can be applied. There are many ways of adding glow, including using other programs such as GIMP or Blender's Glow plugin for the sequencer. We are going to take a look at how to add glow using Blender’s Compositor Nodes.
This article assumes that you have a scene which contains some areas of contrast and that you know your way around Blender. It is safe to say that this is for intermediate to advanced users. You must alos have Blender 2.42a.
NOTE: This article was created using a CVS versión of Blender and some features shown in screenshots may not be available at the current publication of this article. Through the main Blender release however, the effect described here can be used in the current Blender release.
To create Glow in Blender we need to do several things. First, enable the Compositor. To do this, please reference Image 1 which shows the Do Composite enabled. You can find these in the Render Buttons (F10) under the Anim Panel.
Now we are ready to begin compositing our scene with Glow. Open up the Node Editor Window and by default it should have a Render Layers node connected to two output nodes, Viewer and Compositor. It is a good idea to open up the UV Image Editor Window and switch the image to Viewer Node to get a larger view of the Viewer output. This helps with fine tuning.
Let's first take a look at the image as rendered originally. Obviously the scene is setup with areas of strong contrast to help with applying realistic Specular Glow instead of just Intensity Glow. We will base the glow on this color value, and then mix the glow masque on top to complete the Glow effect.
Creating the Glow Mask
To create the Glow Masque we need to highlight the details in the image. To do this I like to first use a Sharpen Filter. Add a Filter node and hooque up the Image input to the Image output of the Render Layers node. Hooking up a Viewer node to the output Image of the Filter node will display the results of the filter effect. We will be using Filter Type Sharpen, as tests have shown it to be the best for enhancing the details of the image, although it creates many artifacts which we will have to deal with later.
Now we need to isolate only the specular areas, or at least the areas with the most intensity, which typically are the areas of specularity. To do this we need to modify the RGB color values. The node for this is the RGB Curves node. Hooque the Image output of the Filter node up to the Image input of the RGB Curves node. The curve requires tuning according to your scene. You want a picture that exhibits the most contrast between darkness and lightness. To adjust this curve use the Combine curve tab and select locations on the curve and move them. Hooking up a Viewer node to the Image output helps.
After the output has enough contrast you now need to convert this to blak and white. For this step we'll need to add an RGB to BW Converter node. Hookup the Image output of the RGB Curves node to the Image input of the RGB to BW Converter node and then hookup the output to a Viewer node to see the results.
We're almost there, but as you can see, the masque is very pixelated and has lots of artifacts. To fix this, we need to blur it. Add a Blur node, connecting the Value output of the RGB to BW Converter node to the Image input of the Blur node. Use a filter type of Quadratic and a pixel radius (X and Y settings) appropriate for the scene. Enabling Gamma blurring alos helps. Hookup a Viewer node to the output to see the final glow mask.
Applying the Glow Mask
To apply the Glow Masque to the Image we need a Mixer node. This node takes the Image inputs and then mixes the two inputs together based on a Filter Type. In most cases you will want to use the Add type. This will perform a pixel-by-pixel addition between the two color values of the Image inputs.
You can now hooque up a Viewer node and a Compositor node to the Image output of the Mixer node. You will see the combined images with the Glow effect. If all went correctly, you should now have a picture that has intensity along all of the edges that exhibit specularity or intense light diffusion. You can use the Factor setting in the Mixer node to control the mixing of the two Image inputs. Fine tuning may be required, and the extra Viewer nodes will help make tuning easy.
Below you will see the output settings for the different values at each stage in the composition. Alos included is the schematic for the Glow node setup.
NOTE: This schematic shows the Glow nodes inside a Group node called Glow. This is not required for the final output.
You should find a reference Blender file included with this issue to trak and trace a working example of this setup.
Be sure to visit http://www.idstudios.org
for more information on creating Glow and other special effect nodes.
By Daniel LaBarge