Black fog is used in SketchUp to indicate where you want a depth-of-field effect. Two images are exported from SketchUp and composited in Photoshop, where you convert the fog image into an alpha channel. The lens blur filter uses this grayscale alpha channel to simulate photographic depth of field.
- [Scott] This week, I'd like to explain how you can create a depth of field effect using SketchUp and Photoshop. The technique hinges upon strategic use of fog to indicate where you want to blur the image. I'm using this kitchen model which comes from my SketchUp: Kitchen Design course in the library. And I've added a vase of flowers here in the foreground. I've done that to give us something interesting to look at which will be in sharp focus, and then, we will progressively blur the image as it goes back in-depth.
Let's go up to the Window menu and open up Fog or expand Fog in the default tray if you're using the Windows version of SketchUp. And then check Display Fog, and uncheck Use Background Color, and then change the color of the fog to pure black. Now we have to adjust these two sliders. There's a near distance and a far distance, let's begin with the far distance which currently right now is set to infinity.
I'll drag that back and you can start to see this black fog appear. What we wanna do is blur most of everything out using this black color in the background, and then I'll use the near slider and pull that forward, and that kind of pushes the fog back a little bit. What we wanna do is have these two sliders close together so that the transition happens relatively quickly but not really, really sharply.
We wanna have a gradient in between there. What I wanna do is kind of adjust this until we blur out maybe some of the sink, but not the flowers. Something like that will work well. Now I'll go up to the File menu and choose Export, 2D Graphic. And I'll give this the name Kitchen-Fog. I'm using the PNG format.
I'll go to Options here and I've set the width to be 4000, and then, let SketchUp calculate the height, which will vary depending upon the aspect ratio of your display. Choose Anti-alias and OK, and then Export. When that's done, let's reopen the Fog window. Uncheck Display Fog. And export a second image without the fog. This time I'll just call it Kitchen and Export.
When that's done, go into Photoshop and open the two kitchen images. Now take the fog image, use the Move tool, hold down the Shift key, and drag and drop it into the other window. This makes sure that they line up. Then you can close the fog image. So this technique requires that we transfer this information into an Alpha Channel.
To do so, Select, All. Copy this information to the Clipboard. Deselect, and then throw layer one in the trash. We don't need it. Then go to the Channels tab and create a new channel by clicking here. This creates a blank Alpha Channel, and then go up and choose Edit, Paste. This copies the information from the Clipboard into the Alpha Channel, which is a gray scale channel so it automatically desaturates the image.
Let's now Deselect. Go back to the RGB channels by clicking up here, and switch back to the Layers panel. Now open the Filter menu and choose Blur, Lens Blur. Select the source as Alpha 1 if it's not already selected. And then, you can control the depth of field effect using this slider. You can have more or less.
I'd like to see part of this blur out, I think that's a nice touch. Somewhere in the middle here looks pretty good, and of course you can fine-tune it with all of these additional parameters. I'll click OK. And I'll press F a couple of times to go full screen, then I'll zoom in and we can appreciate now that we have an attractive depth of field effect using SketchUp Fog and Photoshop's Lens Blur filter.