In my last article, I detailed how to orchestrate global contrast, sharpness, and local detail during the initial RAW processing phase. While I always recommend doing as much of your digital darkroom adjustment while working directly with your RAW file, if you need precise masking (selecting exactly what parts of photo you want to adjust), you will need to take advantage of Photoshop's more precise tools.
I'm going to build on the idea or directing the viewer's eye where you want it to go by explaining a great technique for greatly expanding the tonal range and apparent sharpness in specific areas of your picture. There are several steps involved, but the results are dramatic, so stick with me.
For purposes of this article, I'm going to assume that you have a basic working knowledge of layers and masks in Photoshop. If the concept of layer blending modes is new to you, this will serve as a good introduction.
1. Do as much of your processing as you can in your preferred RAW editor. This will mostly be global adjustments and tweaks by targeted color range, although some masking is also possible.
2. Export your RAW to PSD format. 8 bits per channel is fine for most color work; I recommend 16 bits for B&W, and the Adobe RGB 1998 color space. (The reasons would occupy a whole other article.)
3. Open your PSD file in Photoshop. Duplicate the background layer (Layer | Duplicate or Cmd/Ctrl-J). If you used the Smart Objects feature in Photoshop's RAW editor, you'll need to rasterize the duplicate by choosing Layer | Rasterize | Smart Object from the menu. I also highly recommending giving your layers self-explanatory names to save yourself time keeping track of what does what in complex, multi-layered files. Name this layer something like "+detail."
4. Desaturate the duplicated layer (Image | Adjustments | Desaturate). A monochrome version of your image will hide the color version for the moment.
5. Change the blending mode of the duplicated layer. Essentially what we're going to do is increase contrast very selectively—not along high-contrast edges (you know, the little halo effect of sharpening filters); instead, we're going to increase the difference between adjacent pixels that are similar in tone. If you push this too far, it will just look like noise—pixels that were almost the same tone (as in a blue sky) are suddenly very different in brightness. The trick here is to use a layer blending mode that increases contrast. There are many of them, and they're listed together in the 4th group of blending modes, as shown here. Access them by clicking on the button that usually says "Normal" at the top of the layers palette. These odd names essentially do the same thing (increase contrast), only in varying strengths. Most are much too strong. For our purposes, try Soft Light or Overlay. The monochrome image disappears, and suddenly you have a higher-contrast image. What happens is that any pixel on this layer which is brighter than middle gray darkens the pixel on the layer below it, and any pixel darker than middle gray darkens the layer below it. A pixel that is exactly 50% gray will have no effect. (If you like, prove this to yourself if you like by filling this layer with 50% gray - Edit | Fill | 50% gray at 100% opacity—and then undo.)
6. Choose Filter | Other | High Pass… The optimal radius will depend on the resolution of your image; the higher the resolution, the larger the radius you'll typically use. Tip: Make sure you look at your image at 100% zoom whenever you're evaluating sharpness. For today's digital captures in the 16-22 megapixel range, I usually find 6-12 pixels is about right. WARNING: the enhancement to detail can be so impressive at first, there is a profound tendency to overdo it. Don't!
7. To fine tune the strength of this, you can adjust the layer opacity and the blending mode. Soft Light is the most gentle, followed by Overlay. I almost never need to use the others.)
8. The last but extremely important step is to reveal this enhancement selectively—and this is where too many photographers today get lazy, and kill an image with too much of a good thing. Remember, everything is contextual. If you crank up saturation, contrast, and sharpness everywhere, it's like 1000 voices screaming for the viewer's attention. The idea is to subtly underscore your subject. Also, an unfortunate side effect of the high-pass filter (and similar tools in RAW editors, like the Clarity slider in Lightroom) is a digital halo artifact along high-contrast edges, which we want to hide. So let's add a layer mask: Layer | Layer Mask | Hide All. A black layer mask icon appears, and the effect of the entire +detail layer becomes invisible.
9. Now reveal your detail enhancements only where needed by selecting your subject (feather your selection if necessary to match the optical sharpness of its edges), and filling the selected area with white: Edit | Fill | White. You can use any selection methods you prefer (paths, lasso, marquee, Quick Select, Magic Wand)—or you can simply hand-paint on the layer mask with a white brush. Stay away from high-contrast edges.
10. As you add adjustments in Photoshop, constantly compare the original to your current state by hiding and showing your adjustment layers. I always put all of them into a layer group so I can easily hide and show the entire layer set with one click: Layer | New Group. As your eyes get used to the changes, there is a tendency to overdo it. Comparing will keep you honest!
In the example shown, I used the +detail layer to underscore what I had already done with selective focus and shallow depth of field: I accented the sharpness of the little girl and left the rest untouched. I ended up using the Overlay mode at a layer opacity of 60%. It's subtle, but effective. Try it to enhance texture in rocks, grass, etc.—not in smooth, featureless areas like skies and smooth water. Don't use it on areas that were shot out of focus.