Depth of Focus for C5 using PS CS2

[sailor-ed]

Applying depth of focus (or depth of field; DOF) to a still image render can enhance an image in several ways. It serves to add realism and also helps to concentrate interest on the main subject of the image.

Carrara 5 has a built in DOF effect but I have found it difficult to use and the results often unsatisfactory. Many have long preferred to use Adobe Photoshop with a depth alpha channel to create DOF but Adobe PhotoshopCS2 has a Lens Blur filter that makes accurate, versatile DOF very easy to do and seems to me easier than Carrara's function.

First render the still image with a Depth Alpha Channel. Carrara calls such extra channels "G-Buffers" and if you select the "Fragment Distance" option from the list in the Render room's Output tab you will get an alpha channel where grayscale relates to the distance from the camera. You can only save extra channels in .tiff files or .psd files so be sure to select on of these as the File Format.(on the same tab.)

After completing your render open it in Photoshop CS2. If you look in the "Channels" tab you will see the usual Red, Blue, and Green channels and an extra Distance channel. This channel contains the info that Photoshop will use to create the DOF illusion.

In the Filters menu under Blur you will find Lens Blur. Click on this to open your image in the Lens Blur filter window. Here you will be presented with a panel of various options. See fig. 1. You can make adjustments on the right and the image will update (sometimes slowly) on the left. We will look at only two of the options for now and you can play with the others later.

First, from the drop down menu, select the "Distance" channel as the source depth map. The Blur focal distance slider just below will set where best focus is. You can set it close to the camera (0) or far away (255) (Notice that these correspond to white to black in your Distance Channel). Even easier, you may just click with the crosshair cursor on your image where you want best focus!

Second set the Iris Radius. This corresponds to the depth of acceptable focus. In figure 1 the radius is set quite large giving a narrow depth of field. The green arrows show in focus areas, the red show out of focus areas. In the lower right, where the ship hull goes off to the distance, we can see the range of focus. (Blue bars labeled DOF).

Borrowing a guideline from macro photography, I usually set perfect focus about 1/3 of the way back from the front of the object of interest. In this example that might be somewhere around the middle upright of the right hand window. If you use "faster preview" you can watch the focal point shift as you adjust the Blur focal distance. (Or use the crosshair.) You can then move the Iris radius slider until as much or as little of the image is in focus as you want. That’s all there is to it!

Photographers will find these concepts familiar and there is really nothing hard about it. If you want to get a bit more sophisticated you can go on to adjust some of the other sliders watching their effects in the preview window. In addition to being easy this filter will get you just the depth effect you want and quickly too.

Enjoy.

[bwtr]

I use it myself Ed, brilliant.
I have been using the beta of CS3--WOW new things for the photographer-why would you ever use film or a darkroom nowadays?