Taming Auto Color so it does What You Want it to
So you've played with Photoshop's Auto Color option and had some hits and some misses in terms of making your images look better. If you're intrigued by the possibilities but frustrated by the unpredictability of what you might end up with, read on to find out how to at least partially tame Auto Color so you can better control the results.
As you have no doubt noticed, invoking the Image >> Adjustments >> Auto Color menu option does not present you with any sort of dialog window. As such, it lacks any visible means of adjusting how it works. There is a way; it's just that Adobe hid it. Quite well in fact. Forget all about the actual Auto Color menu option. What you really want is hidden elsewhere.
Go to either Image >> Adjustments >> Levels and click on Options, or if you prefer, go to Image >> Adjustments >> Curves and click on Options. Both will get you to the same place and surprise — there it is. The Options window is indeed titled Auto Color Correction Options. But there are actually two buttons you need to know about to make this work: the Options button that we just clicked on, and the Auto button which you will find right above it in the Levels or Curves dialog. As its name implies, Options allows you to make your choices to influence what will happen. The Auto button will apply whatever you have Options set to without the need to open Options.
Let's look at what the Options window provides.
At the top is a section entitled Algorithms. "Enhance Monochrome Contrast" is the same as the Auto Contrast menu command. "Enhance Per Channel Contrast" does the same thing as Auto Levels, and "Find Dark and Light Colors" is where Adobe hid the equivalent of Auto Color. Ponder over why they didn't use anywhere near the same terminology as the menu command equivalents if you must, but there you have it. For our efforts at taming Auto Color, we'll want "Find Dark and Light Colors."
"Snap Neutral Midtones" tells Photoshop to locate an average color that is nearly neutral which it will then adjust to be truly neutral. This is often worth turning on as it can remove slight color casts without grossly discoloring colors further from neutral that you want to remain unchanged.
The "Target Colors and Clipping" section allows you to select what color Photoshop will use as its targets for black point, midtone and white point and how much it will allow beyond black and white to be clipped. By default, both shadows and highlights will be clipped by 0.10 percent, but you can pick any value between zero and 9.99 percent if you so choose. Generally, you will want to keep the values under one percent though to avoid harsh effects. The target Shadow, Midtone, and Highlight colors themselves can be changed from their default black, middle gray and white values by clicking on each color square. This will open the standard Photoshop color picker where you can pick your desired colors. If you change these, stick with colors not too far off their starting values or you may end up with rather odd looking results.
At the bottom of the Options window is a checkbox labled "Save as Defaults" to allow you to save your choices as the new defaults for the next time you open Options or for when you click on Auto without going to Options at all.
As to what to do with all these settings, you will probably develop your own way of working, but as a starting point, open Options and play with the Shadow and Highlight clipping points. Start at zero or nearly zero for each and increase them until you get what you like. With Preview checked in the main Levels or Curves window, the image will react to the changes you make in Options so you can see what you are doing. I generally prefer Shadows clipped a bit more than Highlights since black shadows can make for dramatic images, but don't overdo it.
After setting both Clip points, check the Snap Neutral Midtones checkbox to confirm if it will do what you want it to. If colors you want to preserve change too much, uncheck it. If you find checking it to be beneficial, next click on the Midtone color square and see if adjusting it improves things. A truly neutral middle gray can sometimes seem a bit cold and warming things up a tad can make for a more compelling image. This is the same reason why many film photographers routinely use a warming filter even when not technically needed.
Even with the ability to tweak the options used for Auto Color this way, you may still need to manually tweak Levels, Curves and use other image adjustment tools to get the best image possible, but you can often get closer more quickly with this tamed version of Auto Color than with any other means. It's well worth exploring.