Fine Tuning Saturation in Photoshop
Color can make for images with added impact. Anyone who has ever shot Velvia knows that. In the digital age, the tempting thing to do is to set your camera for increased saturation, but there are better options. Too much of a good thing is not necessarily better, and you can gain a great deal more control by fine tuning things in Photoshop than by letting your camera do it. Here are a few good ways to do so.
The most obvious solution is to use the Image >> Adjustments >> Hue/Saturation dialog but this has two main drawbacks. First, it gives you no good way to affect only part of an image. And second, there's no going back once you've done it. Yes, you can use various selection tools to partially address the first problem and there's always the History palette for the second, but neither solution is wholly satisfactory. Both problems can be better dealt with by making your Hue/Saturation changes on an Adjustment Layer.
To create an Adjustment Layer, click on the small half-black half-white circle icon at the bottom of the Layers palette or use the menu equivalent at Layer >> New Adjustment Layer. In either case, select Hue/Saturation from the resulting list and you'll end up in the same place. Indeed, it's essentially the same place you get to via Image >> Adjustments >> Hue/Saturation except that now you will be performing your edits on an adjustment layer. If you are already familiar with the Hue/Saturation dialog, you will feel right at home. If you're not, you'll soon become so.
I'm not going to cover everything that Hue/Saturation can do here but will be returning to it next week to cover the rest. What's important this week is how to adjust saturation for which the slider in the middle labeled "Saturation" will come in handy. Moving it to the right increases saturation and to the left decreases it. By default, your edits will affect all colors equally, but you can also use the "Edit" dropdown list at the top of the dialog to select which channel you are modifying. You can pick not only red, green and blue, but also cyan, magenta and yellow. Each channel can have its own saturation level set so you can do multiple edits on one adjustment layer. Click "OK" when done, or select "Cancel" if you decide not to create the new layer. If instead you hold down the Alt/Option key the "Cancel" button will turn into a "Reset" button so you can start over without fully leaving the dialog.
By clicking on the Eyeball icon to the left of your new Adjustment Layer you can turn on or off your changes to see how much difference you have made. You can also use the layer Opacity control at the top of the Layers palette to adjust the degree to which your changes will affect the underlying image. Setting it to 100% will allow the full strength of what you have done to show. Setting it to 0% will make them completely invisible, and so on for opacity values in between.
To the right of the icon for the Hue/Saturation adjustment in the Layers palette you will find a white rectangle that represents what is known as a Layer Mask for that layer. By painting on it, you can control which parts of your image are affected by your changes. Painting with full-strength black will completely mask your changes. Painting with white will restore your changes. Any color between black and white will reveal your edits relative to the brightness of the color you are painting with. Black hides, and white reveals. You can paint with various shades of gray where needed, or simply vary the opacity of the brush you use to achieve your desired affect.
Another useful method of tweaking saturation is to use the Sponge tool in the Photoshop Tools palette. I don't recommend this for major edits since it directly affects the underlying pixels but it can be handy for small changes you know you will never want to undo. We'll look in a minute at how to perform a similar technique on a layer so you can more freely change things without feeling locked in.
The Sponge tool shares a spot in the Tools palette with the Dodge and Burn tools. If you see one of them instead of the Sponge, click and drag to the right with your mouse and the pop-up menu will allow you to see all three.
Once you have found the Sponge tool, the Options palette across the top of the Photoshop window will let you control what it does. The "Mode" dropdown will switch you between Saturate and Desaturate. You can also control the size and other settings of your brush here. By painting with the sponge directly on your image you can make minor saturation adjustments. Be careful though since as mentioned you will be directly altering pixel data.
To do the same thing on a layer, first create a new, blank layer on top of your image. Note that what we are creating here is a regular image layer, not an adjustment layer. Next use the Blending Mode dropdown to change from Normal to Saturation blending mode. You can instead do both of these steps at the same time by holding down the Alt/Option key while clicking on the New Layer icon at the bottom of the Layers palette. This will provide you with a dialog for setting all layer options as you create the new layer.
With the blending mode now set to Saturation, it doesn't matter what color you paint with on this new layer, only how saturated it is. The brush color itself won't show. A brush color with a high degree of saturation will saturate the actual image color where you paint, not impart the brush color. A neutral, desaturated brush color will desaturate the underlying image where you paint. Wherever you paint on this layer, you will change the saturation of the underlying image based on the saturation of your brush.
Rather than constantly trying to change the brush saturation though, it's a lot easier to pick a saturated color and adjust the opacity of the brush instead. You can pick any color you want. I've used green here, but all colors will produce identical results so long as they have the same saturation. Just go ahead and pick a fully saturated color and use the opacity of the layer and your brush to moderate the effect. You will likely find you can get the effect you want with very low opacity levels. I generally start with the layer opacity itself set to around 50% and a brush opacity under 10%. If you overdo it though, just paint over that area on your saturation layer with a less saturated color. You can do so easily if you set your foreground color to any fully saturated color such as pure red or green and your background color to a fully desaturated color such as black or white. To toggle between the two, use the Tools palette or simply press the "X" key on the keyboard, the shortcut to switch foreground and background colors. Each time you press "X" the foreground and background colors are reversed so you can easily paint for a while with one, and then switch to the other for touch ups. If you want to completely undo your changes in a portion of your image, just use the Eraser tool to erase that part of your saturation layer. Unlike with the actual Sponge tool, you can freely saturate and desaturate portions of your image again and again with no loss since you are not changing any underlying image pixels.
Whatever method you choose to tweak image saturation, be careful not to overdo it. Your intent should be to enhance the ability of the image to convey what it was like for you to be there, not create something that never was and never could be. A little can go a long way.