Black Dragon Viewer Guide: #5 Depth of Field

What is it?

Depth of Field is a post processing technique commonly also used in photography where it is a side effect of how the camera is configured to take the picture in question. In 3D rendering it is applied as post processing effect to simulate this effect. It is commonly used to put a certain part of the picture into focus but it can also be used to blur out less good looking parts of the image.

How does it look?

As shown above, Depth of Field blurs the area out of focus, in above's example the focus are the two metal beams in the foreground, right behind them Depth of Field starts to blur, increasing in strength the further it goes back until the configured threshold is reached. In the example above it was used to 'guide' the viewer's focus to the foreground, something out of focus is naturally less interesting to us than something that appears clear, we can use this to put emphasis on something or someone.

How can i use it ?

You can enable Depth of Field by opening 'Preferences' and selecting the 'Display' tab, here you'll find the 'Depth of Field' tab which includes all its options as well.

What can i change?

Just like with real cameras you can configure certain aspects of Depth of Field in rendering, this includes the Field of View, the F-Number, the Focal Length, Circle of Confusion and the Resolution of Depth of Field. In addition you can also customize the time it takes for Depth of Field to switch focus from one focus point to another. Further there are two interesting options to switch between a cheaper but faster Depth of Field calculation and an option to include transparent surfaces into Depth of Field. Especially including transparent surfaces can make a huge difference in how Depth of Field appears.

Caveats

The 'High Quality' Depth of Field is an extremely GPU intensive feature and will quickly drop your framerate if you use a strong blur. It is highly suggested to add Depth of Field at the end of your photography chain as it can make working and finetuning the scene further really annoyingly slow.

Not including alphas into depth can be super useful for Depth of Field, it will make Depth of Field ignore semi transparent particles and stops the 'sudden square blur' that might appear due to this.

Depth of Field stacks badly with Volumetric Lighting, often times Volumetric Lighting will produce 'sharp edges' where objects would otherwise be blurred.

Depth of Field does not scale with resolution, this means that if you take snapshots at higher or lower resolution than your current window you'll have to reconfigure Depth of Field for these resolutions, Depth of Field shares this weird behavior with 'Light Softening', 'Screen Space Reflections' , 'Screen Space Ambient Occlusion' and 'Volumetric Lighting'. Keep this in mind.