Let's return the image now to the state it was in before we applied the High Pass Filter. You can go the the history palette and click on the level just before the one that says High Pass Filter.

(If, for some reason, your history has gotten scrambled, just set up your layers as before: original on bottom, blurred layer next, and a copy of the original on top)

This time around, we're going to set our blending mode and opacity BEFORE applying the High Pass Filter.

Go to the top layer (the copy of the original) and set blending mode to Linear Light, and opacity to 50%. It should look something like this.

Open the High-Pass Filter and and pull the radius slider all the way to the left. The value is .1 pixels.

The image to the right is magnified to 400%. Note how the level of detail changes as you increase the radius. Your readings will vary somewhat, depending on the resolution of your image, but the same thing will happen as you raise the setting. Different levels of detail will become more pronounced.

What we are left with, after this somewhat complicated demonstration, is really a simple idea: Various settings of the High Pass filter emphasize different levels of detail. Some of that detail is desirable. Some, we want to get rid of. It's actually pretty simple to accomplish.

THE WORKFLOW
It's always a good idea to apply some conventional retouching to the image before embarking on this procedure; large blemishes, warts, brusies, lines and discolorations should be minimized as much as possible. But you don't need to be a fanatic about it. As I said at the outset, I performed no retouching on this image before taking it through these moves, though, as I mentioned, the skin was in good condition to start with. Sometimes, though, it helps.

• Copy the original (or merged layers) into five new layers.

• Name the first layer Blur and leave it in Normal mode at 100%.

• Change the other four layers to Linear Light mode and set their opacities each to 50%. Turn them off for now and return to the Blur layer.

BLURRING
This is the step that wipes out everything, in order that we can selectively replace only what we want. We've used Gaussian Blur so far in our examples to accomplish this.

The advantage with using Gaussian Blur is that it is precise. Knowing the radius of your blur provides you with a guide for measuring the radius for your high-pass filters. The disadvantage is that it is sloppy and hard to control. Color bleeds from one area to the next and with skin that becomes obvious next to dark backgrounds, hair, clothing and shadows.

One way to get around this has been to create a skin mask like the one to the right. Then, using it as a selection, the skin gets copied to a new layer and the blur gets applied to that. This works better, in that dark regions adjacent to skin don't bleed their colors into skin tones. But it creates a softness at those edges anyway, simply from blurring. There are ways around it, but I prefer a different method altogether.

THE LENS BLUR
The Lens Blur filter was introduced in PS7, I believe, and its primary function is to mimic depth-of-field effcts. It uses a grayscale alpha channel to determine how much blurring to apply to different parts of the image. A properly applied gradient from white to black can create a believable effect of blurring increasing with distance. It is far cleaner than trying a similar operations with the gaussian blur. It adheres to the mask precisely, with no pixel/color bleed. And we're not using gradients. Our only concern is with black and white areas—to blur or not to blur.

I've been using a Lens Blur in place of Gaussian Blur, with superior results. The downside: the radius settings don't seem to match those of the Gaussian blur, so you will need to work a bit more intuitively. This, as it turns out, is not too hard to do.

So, shiny new skin mask in place as one of your alpha channels (named, hopefully, skin mask, or something to identify it), let's see how it works.

When you open the Lens Blur Filter, there is an impressive and daunting array of parameters. I haven't found much use for any of them other than Radius, Shape and Distribution.

• At the top under Depth Map, select the alpha channel with your mask (which, if named properly, will be easy).

• Leave the Blur Focal Distance at 0. If your preview shows the blurring happening in reverse, check the Invert box.

• I use the Hexagon shape because it seems to be stronger. It's not really important. Choose to taste.

ª At the bottom I check Gaussian for Distribution.

• It's the Radius slider that is of interest. By now you should know what it is we're looking for with this step. Vary the setting until you have those smoothly blurred areas of color.

If you see that you are losing some shadow detail, or that you are getting some color drift from shadow areas into skin tones, click Cancel and return to your mask and paint them out. Notice how in the mask I drew, I excluded the nostrils.

Once your preview is to your liking, apply the filter. It takes a bit longer than a normal Gaussian Blur, and the result is a little strange. Sharp eyes and mouths in a smooth sea of washed out skin. But that will change.

ADDING DETAIL
Up until now, the steps have been pretty straight-forward, and the goals clear. Now it becomes slippery, in that there are an infinite number of ways to set the appropriate values to get the effect desired. It's a matter of taste and preference. I'll take you through the settings that I chose, and try to explain why (not always an easy thing) but it's not as important to match my approach as to become comfortable with what is actually going on. Keep in mind, your numbers will be different. In fact, were I to do this again, my numbers would probably be different. And any of these parameters can be enhanced, modified or expanded.

We have four layers to work with. The goal will be to apply the High Pass filter to each of them, with a distribution of radius settings that more or less evenly captures a full range from small to large detail. Once we determine the initial radius, we can then determine the settings for the remaining three layers by simply reducing the settings each time by an equal value. But what should that initial radius be?

Recall that with a Gaussian Blur, we knew the setting that would return the blur to its original state: it was the same as the Blur radius. We don't have the same precision here, but it's pretty easy to increase the radius of the High Pass filter until the image looks more or less like the original. Our starting radius will then be a value lower than this. (Remember, we're trying to minimize the large detail.

For this image, a radius of 30 pretty much replicated the original state. So I reduced the setting to 20 and that became my starting value, the results shown here. Compare it with the third image (the starting image) and you can see that we've already begun smoothing some of the blotchiness away.

Our ending value will almost always be a radius of 1 pixel (occasionally less, but not often), so it's simple arithmetic to figure out the intervening settings. I chose 20, 13, 8 and 1 as the settings for each of my High-Pass Layers.

This is how it looks after all four layers have had the High Pass Filter applied. Things look pretty ugly; but now we start playing with the layer opacities.

We will drastically reduce the opacities of the layers with the largest radius settings, and increase the overall effect of the layers with the smaller settings.

Here is the arrangement I ended up with. The layer names reflect the High Pass settings each used. I arrived at this by pure trial and error and might well have chosen different values. But these work. Trust your eye.

The opacities are as follows:

20: 20%
13: 80%
8: 80%
1: 100%

I then grouped the two top and two bottom layers into their own layer sets, and adjusted the opacities of these as well.

Low End: 20%
High End: 75%

Finally, I applied a Gaussian Blur to each of the High Pass Layers, to return things to a realist focus. The blur radius increases as the High Pass radius increases. I stayed conservative. Experiment to see what works.

1: .5
8: 1
13: 3
20: 6

And, finally, I grouped both layer sets, along with the blur layer into a master layer set and applied our original skin mask to everything.

NOTE: there's nothing hard and fast about using four detail layers. Any number could be appropriate. You might want to cluster detail layers towards the smaller bands. Each image will have different characteristics and requirements.

And here is the result of all this dithering with opacities. Not too shabby, I think you'll agree.