Now that we have finished with the first two Cs: Crop and Contrast, we can begin to work on overall color. Hopefully, the process of cropping and adjusting the contrast has eliminated or revealed any problems the image may have with color. Ideally, you would wish for perfect color but that is seldom the case. If it is, you and your equipment have conspired to reveal a perfect scene in all its glory. Let’s pretend things are otherwise.
The first thing I look for is any image is an overall color cast. Most of the time color casts are a result of the color of the light illuminating your subject. When you shoot in incandescent lighting, overall orange casts pervade your image. Shooting in fluorescent can produce a yellow or green cast.
In this product photo of transmissions, the light source was mixed-as it often is. There is diffuse sunlight coming from the windows behind, fluorescent overhead fixtures and incandescent spots. The tiles on the floor where mostly white so we know we have some yellow and some orange casting the image.
There are a couple of ways to correct these images. As always, ideally, you should get it right in the camera and have your white balance set as closely to the lighting conditions as possible. One way to do this, provided you shot RAW is to adjust the white balance on the RAW file by selecting a neutral item with your white balance eyedropper or moving the white balance and tint sliders.
If the cast has appeared after you’ve done quite a bit of editing or you shot the original image in JPG, you have to rely on other methods.
Conversely, the image may exhibit color casts only in certain areas or in specific color ranges. These are usually the result of subtle magnification of the lighting in a scene and/or the use of different lighting on specific areas of your subject. The cloud shot above has violet shadow areas in the clouds and needs a specific adjustment. Another example of this would be a portrait of a person shot next to a window where the person is properly balanced but the interior surroundings are cast by the interior lighting.
Thus, the task for you, as always is to evaluate your image and determine if the cast is:
- A single color cast across an entire image
- Multiple color casts across the entire image
- An unnatural color in a small area of the image
- An unnatural color in a small color range of the image
Depending upon your evaluation you will tackle the problem in different ways.
Color casts across the entire image are best handled by using a Channel Mixer type of function. There are Color Balance Tools, Target Balance Tools, Channel Mixers, Hue Saturation and Lightness, and a host of others depending upon your Image Editing application. Some programs have several methods of adjusting color.
In this dialog from Corel Paint Shop Pro Photo you can quickly adjust a color cast to a more acceptable balance.
When you have a selective area in an image where the color is off, you can usually turn, with an expectation of success, to a Hue Saturation and Lightness adjustment, hereafter referred to as HSL. I tend to prefer Adobe Photoshop‘s HSL tool.
The tool allows you to split the six color channels and then use an eyedropper to assign the color range you wish. In addition, you can use the dual sliders at the bottom to expand, contract and feather the range of the color adjustment. You can control the hue(the movement of the color in to the adjacent areas of the color spectrum), the saturation (the amount of a give color-it’s richness) and the lightness (how light or dark that color appears).
To take out those purple shadows, I selected the magenta channel as it is little used in my image and then used an eyedropper to select the purple in the clouds. I then made a course negative saturation adjustment to see if I had all my color selected. I was missing a little of the magenta area so I slid the slider to the right to expand my selected range. Then I adjusted the saturation, hue and lightness to my taste and created the color correction you see here.
Now, we have removed a cast and corrected a single color range so we that we have an image with reasonable color fidelity. Still, the color looks a little flat. I remember those greens being a lot more poignant. In the next installment, we will talk about correcting image saturation.
Rikk Flohr © 2008