In amongst all the other goodies in Adobe Photoshop 7, you may have missed Auto Color entirely. Or, you may have chosen it from the Image > Adjustments menu, found that it gave you a fairly unattractive, cold, contrasty image and decided it was as useful as all the other auto-adjustments -- which is to say, not terribly useful. In its fully automatic mode, Auto Color may disappoint, but if you dig a little deeper, you'll find that with a very little work, it becomes a powerful tool for making your major initial corrections -- call it "Semi-Auto Color."

Confessions of a Latter-Day John Henry
I've always been profoundly distrustful of auto-anything when it comes to working on images -- auto-corrections might be OK for amateurs and newbies, but they had no place in a professional environment. I always believed I could do a better job, faster, than any algorithm. And it's true that the auto-correction features offered by previous versions of Photoshop were pretty much image-wreckers -- Auto Levels seemed designed to destroy highlight and shadow detail while introducing massive color casts, while Auto Contrast contented itself with destroying highlights and shadows while preserving whatever color cast was present.

My first hard lesson was the harsh realization that Nikon's auto-focus did a better job, faster, than my 40-something eyes could. So when I first saw Auto Color in an early alpha version of Photoshop 7, I resisted the inclination to ignore it, and began exploring.

I've been using Auto Color ever since, and I've become sufficiently convinced of its usefulness to recommend it as the first thing to do with uncorrected images. I use it on raw scans and digital captures, and it's proved to be an enormous time-saver. But you do need to use it with some care. The guidelines laid out in this article will get your images much closer to where they need to be with a few simple tweaks. Failure to follow these guidelines will probably get you over-contrasty images with blown highlights, plugged shadows, and a color cast.

Automatic, but You Need to Press the Buttons
Don't choose Auto Color from the Adjustments submenu-it doesn't offer the control you need. Instead, use the controls that you can reach from either the Levels or Curves dialog box -- I prefer using Levels because the dialog is smaller, so I can see more of the image. To reach the controls, click Options in either dialog box to open the Auto Color Correction Options dialog box shown in Figure 1.

Figure 1: Access Auto Color Correction Options from the Levels or Curves dialog box.

Here you'll run into the first little gotcha. Unless you take steps to make it do otherwise, the Options button in Levels and Curves always defaults to Auto Levels, and to make matters somewhat worse, the options in the Algorithm section of the dialog box have a completely different, albeit more descriptive, label than the equivalent menu commands. Here's the secret decoder ring:

• Enhance Monochrome Contrast is the same as Auto Contrast.
• Enhance Per Channel Contrast is the same as Auto Levels.
• Find Dark and Light Colors is the same as Auto Color.

So the first order of business is to make the dialog default to Auto Color instead of Auto Levels -- you only have to do this once. Choose "Find Dark and Light Colors," (ignore what it does to the image for now -- you'll undo it as soon as you've closed the Levels dialog box) and check the "Snap Neutral Midtones" checkbox.

Then click the "Save as defaults" checkbox, as shown in Figure 2.

Figure 2: Choose Find Dark and Light Colors and check Snap Neutral Midtones, then Save as Defaults.

The goal of this step is simply to ensure that when you press the Options button you get Auto Color rather than Auto Levels, so click OK to close the Auto Color Correction Options dialog box, and click OK again to close the Levels dialog box (or just hit the Enter key twice). Then immediately hit Undo to undo whatever havoc the default settings wrought on your image.

Now you're ready to start using Auto Color on images. The Auto Color Correction Options dialog box allows you to adjust quite a few different parameters, but I generally only tweak three settings: the highlight percentage, the shadow clipping percentage, and the neutral midtone target color, in that order. The default clipping percentages -- 0.50% for both shadows and highlights -- seem to harken back to a bygone era where capture devices were a great deal noisier than they are today. For most images, this is much too high a setting, tending to blow out highlights and block up shadow detail. The neutral midtone target color is set by default to RGB 128 gray, which often results in a rather cold color balance. In most cases, I end up raising the red value slightly, and lowering the blue by about the same amount.

Let's look at how this works in practice. The image in Figure 3 needs serious help (this is what happens when undeveloped film winds up going through x-ray machines about twenty times because the airline lost your luggage).

Figure 3: This image needs serious help!.

If we simply accept the default settings, we get a very high contrast and rather cold rendering, even if it's a great improvement over the raw image. Highlights such as the tops of the buses are blown out to solid RGB 255 white, and the shadows are very murky, as shown in Figure 4.

Figure 4: We need to repair the blown-out highlights and murky shadows.

We can improve matters greatly by adjusting the clipping percentages. The image updates as you change the settings, and the info palette provides before-and-after values, so the whole process is quite interactive. When you're starting out, and just getting a feel for the way the controls work, I suggest setting the shadow and highlight clipping percentages to 0 (no clipping) as a starting point, and increasing them gradually from there until you get the result you want. The change from 0 to 0.01% is bigger than you might expect.

An easy way to see what's happening as you adjust the clipping percentages is to use the arrow keys instead of typing numbers into the fields. Highlight the field whose value you want to edit, then press the up or down arrows to increase or decrease the percentage in 0.01% increments: Add the Shift key to go in 0.1% increments instead. That way, you can place the cursor on a highlight or shadow in the image and watch what happens to the values in the info palette as you adjust the clipping percentages. Using this technique, it takes me about three seconds to decide that the shadow clipping percentage should be 0%, and the highlight clipping percentage should be 0.02%, producing the result shown in Figure 5.

Figure 5: Adjusting the clipping percentages to 0% for shadows and 0.02% for highlights gives much better results.

The aforementioned edits produce a decent dynamic range -- the shadows are pleasantly open, and the hottest spots in the highlights are all still below level 250 -- but the color balance is still rather cold. Adjusting the midtone target color lets you fix the color balance in the same round of edits. Click on the midtone gray swatch in the Auto Color Correction Options dialog box to open the color picker, which in turn lets you change the target color, as shown in Figure 6.

Figure 6: Now change the target color to fix the color balance.

As with the clipping percentages, changes to the target color are immediately reflected in the image, so the process is interactive. You can adjust the target color either by changing the numbers in the numerical fields (the arrow keys work here too -- up and down arrows change the value by 1, adding the Shift key changes the values by 10), or by dragging the little circle around in the color swatch, or a combination of the two. (I often find that adjusting the HSB numbers is quicker and easier than adjusting the RGB ones.)

In this case, I obtained the result shown in figure 7 by first raising the Red value and lowering the Blue, then dragging the circle in the color swatch until I obtained the visual result I wanted.

Figure 7: Changing target color is interactive so I raised the red value and lowered the blue until I got the result I wanted.

It's Not Automatic, but It IS Quick and Easy
This is one of those techniques that takes a great deal longer to explain than it does to execute, though my painstaking blow-by-blow description might lead you to believe otherwise. The quick version goes:

1. Open Levels.
2. Press Options.
3. Adjust Shadow clipping.
4. Adjust Highlight clipping.
5. Click the Midtone swatch.
6. Adjust the Midtone color.
7. Click OK to close the color picker, click OK to close the Auto Color Correction Options dialog, click OK a third time to close Levels and apply the changes to the image.

With a very little practice, this becomes a very quick and easy way to optimize the dynamic range and fix the color balance in a single step. To show you just how flexible this technique is, here are a couple of images that need less desperate intervention than the one we've been working on so far.

Figure 8: This image has too much yellow.

In this late-afternoon digital capture of San Francisco's Painted Ladies, the golden light is a bit too golden. Three quick tweaks, and the result they produce, are shown in Figure 9.

Figure 9: That's better.

Another San Francisco landmark shown in a very flat capture in Figure 10 needed a little shadow and highlight clipping to restore contrast, and a very slight midtone color adjustment to produce the result shown in Figure 11.

Figure 10: This image has no contrast.

Figure 11: Now it has better contrast.

There's only one thing I don't like about Auto Color. It's so easy that for those of us who have been used to wrestling images into shape the hard way, getting 90 percent of the way there in three quick tweaks is almost anticlimactic. But I'm getting over it!

Read more by {link http://www.creativepro.com/author/home/40.html Bruce Fraser.