Orban Design

Providing the highest quality architectural rendering for Charlottesville and beyond.

DOF part II – depth of field calculated by rendering software

As mentioned in the first post on Depth of Field, there are some shortcomings to creating a DOF effect in a rendering entirely as a post-processing operation. The biggest shortcoming is that any distant reflections showing up in reflective materials in the rendering will be uneffected by the zdepth layer that the software generates. Here is an example of an interior rendering with a reflective granite countertop. As you can see, Zdepth takes care of blurring the distant subjects in this view – the dining room and the trees outside. However, the reflection of the trees in the counter is not affected at all!

Residential Interior rendering
In considering the advantages and disadvantages of rendering software generated DOF, here are some of the pros and cons:

  1. Good: depth of field effect is realistic – based on phsyical properties of the camera, and consistently affects all aspects of the image including reflections and refractions.
  2. Added difficulty: takes an understanding of camera values such as aperature and focal length to successfully tweak the amount of blur.
  3. Bad: no quick way to adjust settings on the fly – need to recalculate a new rendering for each adjustment.
  4. Bad: not as smooth as photoshop blur.

What I end up doing in my renders is to use the best of both options. Where there are reflections, I will run a rendering with DOF turned on, and at the same time generate a zdepth layer that I can use post-process to give the blur a nicer appearance. Here is the final result using a combination of both rendering engine DOF as well as post-processed DOF blur.

final rendered view of residential interior

Photorealistic rendering and depth of field (DOF)

One of my current favorite methods of enhancing the photo-realism of a rendering is by using depth of field (DOF) blur.  With my interest in photography, I like to find the ways I can blur the line (so to speak!) between a computer generated image and a photograph.

When a computer rendering is generated, it produces an infinite depth of field – everything is perfectly in focus, near and far. On the other hand with a camera, the lens’ aperture mimics human vision in permitting the camera to only have accurate focus within a specific range of distance, also known as the depth of field. The result is blurriness further away from the object that is in focus.

Many of the rendering programs have methods to add DOF to an image, with trade-offs resulting from different approaches. The method I am using for my example is to generate a map of the 3D depth in the image as a layer. This has two main advantages, and one big disadvantage:

  1. Good: speed – it’s faster to render, as the rendering software doesn’t have to also calculate the DOF.
  2. Good:  I can control the blurriness in Photoshop without having to render the image again.
  3. Bad: reflections are not blurred, nor are objects through glass.

Here is the base image I am using for my example and the “zdepth” layer shown next to it:

And without further ado, here are two versions of DOF blur – one focusing on the fireplace, and the other focusing on near objects.

As you can see, DOF can be very useful to direct the eye towards a focal point, or emphasize certain elements of an image. The first image blurs the foreground to highlight the stone fireplace. The second downplays the chimney in favor of a more photographic style where the detailed foreground is given more weight. This second approach helps give the room a sense of depth as the side walls and fireplace recede into the distance.

Used judiciously, (and once the other elements of the rendering have been accounted for – lighting, materials, contrast, etc.), depth of field can be one more tool to bring a rendering to life.