As we’ve mentioned before, Curves is probably one of the most powerful tools in Photoshop when it comes to contrast adjustments.
One thing we don’t mention quite as much is that it is just as capable at managing colour adjustments, and allows an impressive level of control over the colours in your image. When combined with layer masks, you can selectively edit the colours of various aspects of your scene, although it takes a great deal of practice to do precisely.
Important note: when doing fine colour work, it’s absolutely essential to have a properly calibrated monitor. Monitors vary widely in terms of their default settings, and monitors can also vary in terms of their white points, brightnesses, and contrast ratios.
A small investment in a good external colour calibrator is a wise move for any serious photographer! We’ll dig into this a bit more in an upcoming post about colour profiles.
As you may know, most digital images are stored in the RGB colour mode , meaning that they are actually made of 3 separate greyscale ‘channels’ or bitmaps: one for red, one for green, and one for blue – RGB. In the red channel, the brighter a pixel is, the more it corresponds with red, and the same follows for green and blue.
You can get a better idea of how this works by opening an image and taking a closer look at your ‘Layers’ palette.
There should be tab named ‘Channels’, which will show you the 3 channels of your image and how they combine to form the RGB image you know and love. You can select each one to see their individual contents, or hold down the Shift key and click to combine just a couple of them.
The general principle for doing colour work with Curves is the same as doing general contrast adjustments, except that you can adjust each colour channel individually for maximum control. Let’s dig into the Curves panel and see how it can be used more effectively than just for global contrast adjustments.
Most important for colour work is the channels dropdown, which allows you to select which colour you’re going to be modifying. While there are only 3 colour channels, it’s possible to adjust any of the colours visible in your image by combining them. Also important are the tools on the left of the Curves panel, which offer you a number of quick ways to interact with your adjustment settings.
The tool represented by the small hand (for whatever reason, it is not named) is very useful when it comes to working with Curves, as it allows you to set points on your adjustment curve by moving your mouse over various parts of the image. Not only can you quickly set up the correct points on a curve, but you can easily identify which parts of the image correspond with particular areas of the Curves histogram.
Take a look at this example – at first, the image may seem properly colour-balanced, but a closer inspection reveals that the tint is slightly too red to be quite perfect. A lot of these decisions will depend on your personal preferences, of course, but let’s try tweaking it a bit with a Curves adjustment on the red channel.
Just a tiny downward adjustment in the midpoint of the Red channel in Curves corrects the slight tint. You’ll note that in the Curves panel, when you switch back to the RGB mode, you’ll see there is an additional adjustment line in Red, representing the specific adjustments made to that channel. If we’d modified the other channels, you’d see a corresponding line for each one.
If your image has a white point or a neutral grey point, you can try a quick and easy way to remove colour casts from your images using the eyedropper tools. You’ll see 3 of them: one for highlights, one for midtones, and one for shadows. Using these will adjust both the overall contrast values and the channel-specific colour values to try to automatically.
If you’re interested in a quick video tutorial, Steve has put together a fantastic short video about using the Curves eyedropper tools to adjust the colour tints in your photographs that often appear when shooting using automatic settings. Check it out here!
Depending on your image, they may not do the job perfectly, but they can be a great help when it comes to large-scale adjustments, and they’re a real help when you’re just getting the feel for how Curves works. If it takes you some time to get adjusted to this new method of working (sorry, I couldn’t resist), don’t worry, it will come with practice!
I had a colleague years ago who struggled with using Curves adjustments for very fine colour work. We were doing colour adjustments of various furniture product photographs using Photoshop, but he couldn’t get it quite right.
One morning he came into the office and told us that he’d had a dream about how the channels interconnected, and suddenly it all just ‘clicked’ for him. We laughed at the time, but almost immediately he became one of the best colour editors I’ve seen yet. Hopefully it won’t cause you quite that much trouble, but then again, you never know what might make it click for you too!
One last thing to be careful of when you’re doing a lot of fine colour work is just how adaptable your eyes are.
If you spend a long time staring at any part of a particular image, it can be easy to lose your sense of neutral colour balance, so you might want to keep a neutral grey card handy to ensure that your eyes aren’t overcompensating. If the card starts to shift in colour, it’s probably time to take a break from editing!