Variations on a Theme
Photoshop is a complex program, and it takes getting used to. But sometimes people are just looking for a quick and easy way to visually make tonal corrections to an image, and for this Curves and such may be overkill. One of the underused features in Photoshop is a tool called "Variations."
Located at the bottom of the Image >> Adjustments menu, Variations allows you to quickly see how your image would look with slight color shifts in each direction, as well as what it would look like a bit lighter or darker. A small copy of your current choice sits in the middle of the window, with each of the available variations arrayed around it. By clicking on one of variations, the central image changes to match your selection, and each of the surrounding thumbnails updates accordingly.
Say you think an image would look better a bit more magenta. Click on the magenta variation and the central image will change to match what you clicked on and the magenta thumbnail will get that much more magenta. Click on the magenta thumbnail again and again to repeat the process and increase the effect. With each click, the green thumbnail variation that lies directly opposite the magenta one will change to what your main image originally looked like since green is opposite magenta on the color wheel. Everything shifts to reflect the change corresponding to its place relative to what you clicked on. Want to undo a change? Just click on the opposite color. Or click on an adjacent color to take your image in a different direction. It's all very visual and intuitive.
To provide for fine tuned control, Variations lets you control Shadows, Midtones and Highlights independently as well as adjust the degree of change for each click from fine to coarse. You can also switch to controlling saturation rather than hue. In this mode, the display changes from having six thumbnails, each with a different color cast, surrounding the main one, to having just two choices, one with less saturation on the left of the central one, and one slightly more saturated on the right. You can toggle between Shadows, Midtones, Highlights and Saturation as needed while adjusting an image. With each click on a variation, the thumbnails change and you can decide what you which you want to work on next. To keep you out of trouble, you can turn on the display of clipping in each of the variations. Although I haven't found it to be useful, you can also save and reload Variations settings for later use.
One odd thing about Variations is that, unlike pretty much everything else in Photoshop, it will remember your choices even when you switch from one image to another. Rather than looking as it should, the default for the central image will represent whatever your choice was for the last image you were working on in Variations. Closing and reopening Photoshop will reset it thankfully, but there's an easier way. At the top of the Variations window is a small version of both your original image as well as your current pick. If you find that the central image doesn't look the way you expect it too when you open the Variations dialog, just click on the Original thumbnail all everything will reset back to normal. You may find it to be a good habit to click on Original as your first step when opening Variations just to make sure you don't end up with any unexpected surprises.
Unfortunately, Variations only works on 8-bit images and if you want to get the best results out of your images you probably do all your editing in 16-bit mode. But that doesn't mean that Variations isn't still useful. Sometimes half the challenge in optimizing an image lies simply in envisioning what would look best. Once you know where you are headed with an image, making the actual adjustments is that much easier. And for this, Variations is great, with a little help. First make a copy of your image with Image >> Duplicate. Then convert your copy to 8-bit mode with Image >> Mode >> 8Bits/Channel. Now you can have all the fun you want with Variations on your 8-bit copy. When you get the look you want, click on "OK" as normal. You'll still have to use Hue/Saturation, Curves and so on (hopefully via Adjustment Layers) to achieve a similar effect in 16-bits on your original image, but at least now you know what's possible.