Here’s a quick and flexible way to emulate the look of fog in the background of an image. I recently used this technique in the visualization of the Agami House in Yaffo. It’s true it might not look real enough but for most cases this really looks good enough and you have the added bonus of fast render and flexible edit inside Photoshop if the client ask for tweaks.
Adding the fog layer
You’ll start with the original render without any fog in it as you see below
On top of this image you’ll add the fog layer – Full frame of pure white color masked out by the VRayZDepth render pass.
If you need to adjust the fog location relative to the camera you can play with the ZDepth image levels, instead of re-rendering the image after changing the VRayZDepth parameters, This way you can quicky move the fog in and out as i did in the example below.
But this is not that good since the beautiful sky is now covered with white color. In order to get this right, and actually more true to the way fog behaves in reality, you need to change the pure white layer to a gradient with pure white at the bottom that shifts to transparency as you move up… this way the fog will be limited to near ground areas.
You can see above the end result with the fog layer at 100%. You can decrease the impact of this layer to fine tune the general effect, or even mask out specific areas to emphasize exactly what you like.