I’m not advocating violence here. In tradespeak, creating a knockout means removing the subject of a photo from its background…hopefully with all the transitional edges, such as flying hair, semi transparent areas, and surface reflections intact. The idea is to be able to put that subject into an entirely new background.

Lightroom 2 can be a great aid if you have objects on a plain background, such as a photographer’s seamless, in making it easy to do amazingly accurate knockouts of subjects that may have very complex edges. I find it especially useful in removing a model from the background so that a more interesting background can be substituted and lit it its place. If your subject’s edges are mostly (or, better yet, entirely) darker or lighter than the background, you can make a very clean knockout by increasing the contrast between the background and the subject. For instance, if it’s a portrait you’re knocking out, use a white or very light background (the more neutral, the better) for medium to dark-haired (and clothed) folk and a black or dark gray background for blondes and lighter-haired folk. Here’s a portrait, as it appeared after color balancing, in Lightroom:

Now, the problem is that, often there’s some slight shading in the background or subject that keeps it from contrasting with the outline of the subject. Although the original background was stark white, it wasn’t as brightly lit as her face. That makes it harder to make the precise transitional mask that would be ideal for making the knockout.

Lightroom 2 has localized corrections that make it easy to enhance that contrast. Then you just export the picture to Photoshop and use a few tricks to make the mask. In the Develop Module, I set up a Custom localized adjustment that uses both Exposure and Brightness, each boosted to about 80. I make the Brush a large size and reduce the Feathering to “next to none” and turn on Auto Mask. I make sure that the “X” in the center of the brush circle stays on the background and never touches any of the other colors. As a result, the Auto Mask selects only the shades of the background color…never the hair, blouse, or skin. Once I’ve got the whole area covered, I place the cursor right over the brush spot and the background turns red (because that was the color I chose). I can then easily see what the Auto Mask has protected. Then I just drag the Amount slider all the way to the right. Here’s the result:

Now all I have to do to make a mask is open the file in Photoshop, then duplicate the background layer and choose Image > Adjust > Threshold. Everything turns to either black or white. So then all I have to do is select inside the black area and fill with black. The result looks like this:

Next, I duplicate the background layer again and raise it above the black and white image. I then choose the Magic Wand and make sure that Contiguous isn’t checked in the Options bar, set a fairly narrow Tolerance, and click in the black part of the image with the black and white layer selected. Now everything that’s black is a selection. I choose the top layer (copy of the background) and click the Mask icon at the bottom of the Layers palette. I can fine-tune the mask by choosing Refine Edges. I find that works better if I’ve first added a new 50% gray layer just under the top layer and then choose to show the underlying layer while I’m refining the edges. When that’s done, I just replace the gray layer with a copy of the photo of the background I want to use, defocus it as makes sense, and then do any necessary retouching before I save the image back into Lightroom. Here’s what I finally ended up with, just in case you’re curious:

If you want to know how I did all the rest of it, you can check next weeks Podcast episode on www.pixelicious.info.