Troubleshooting Photos –
About Auto-Correction Tools
Traditional color correction of photos is one of the most user-hostile activities you can perform with a computer. Correcting color in CMYK for commercial printing can be tricky enough, but doing so in RGB, for desktop printers, is a skill so arcane and counter-intuitive as to justify the belief that aliens walk among us. Accordingly, software makers have put a lot of energy into auto-correction tools, functions and routines that concentrate a lot of learning into a few mouse clicks. Sort of. If you blindly trust a "one-click" fix, you can make the picture worse. To get full value, it helps to know what you're doing and how to use these tools in ways that improve your results.
Although the practice of color correction can be complicated, some of the underlying ideas are quite simple. For instance, a great many pictures are spoiled by having been taken under a strongly colored light. This may be the red of sunset, the green of fluorescent lights or the blue of winter daylight – whatever it is, it distorts the colors and spoils the picture.
The correction for a picture with an overall unwanted color – a color cast – is simple. You find an area that should be neutral (true grey, white or black, with no color other color present) and determine what color is in fact there. That color can then be presumed to be the value of the cast that covers your picture – remove that value and presto, the cast is gone and your picture is immeasurably improved. Photo-editing software uses this principal in a variety of ways. Upper end applications have tools for targeting white, grey and black. Packages that concentrate on user-friendliness, such as Photoshop Elements, combine the three into one Remove Color Cast function.
These tools can do a good job – depending on the reference point you choose (the reference point need not be large; ones used in the Dragon-boat photo below is a tiny dot of white on the water). The photo below has a number of casts in it: an overall slightly blue cast that comes of being shot in shadow with bright light behind, plus a number of weaker colorations covering limited areas (known as 'local casts'), caused by light reflecting from the Dragon-boaters' highly colored clothes. Therefore, the colors that are changed vary with the spot you pick, with interesting results for the picture.
This Dragon-boat competitor is tired, but not so exhausted that her skin should have a blue tinge. Three targets were chosen for Photoshop Elements' Remove Color Cast eye-dropper: her competitor's wristband, the white in the red-and-white side of the boat at right and the white letters on the jacket of the paddler behind her. Interestingly, if you choose the white buoy just visible at left beyond the man's neck, which is genuinely white, the picture remains bluish. Choosing the letters, which are affected by the same color cast as the people, gives a more pleasing result.
The changes are just as dramatic if you choose from the different blacks, in large part because black dyes for clothing often have a strong color component to make them visually more interesting.
Experiment, Experiment...
On occasion, it may not be clear which tool is best for the job. In fact, you may want to experiment with different tools or different combinations of tools to achieve the desired effect. The photo below is one that most auto-correction tools will have trouble with. A large part of the picture is black (but not just one black – many blacks, each based on fabric dyes that contain colors that help make the blacks visually richer and more interesting and each subtly affected by other adjacent colors in the chair and on the walls). The presence of so much darkness totally confuses automatic adjustments that assume that most of a picture's tones will be in the middle.
The original under-exposed picture was taken with flash bounced from a pale yellow ceiling, so there is a yellow cast as well as not enough light. The first remedy, in autofix, was Photoshop Elements' Auto Smart Fix command. This did a very good job, but also made the whole picture look as if it had been printed on plastic and backlit, particularly in the skintones.
sampled relies on using the black, white and grey eyedroppers in the Levels dialog (plus some hunting around different spots on which to click, as in the Paddler picture above). This improved some parts of the picture but left it too dark in the shadows. Further tinkering with the Levels histogram (see below) yielded a picture very similar to the one achieved by Auto Smart Fix without the backlit look. levels doesn't have the open shadows of autofix, but it looks more realistic overall.
The point of this tinkering is not to disparage auto-correction tools but to show that while they are capable of giving reasonable results with average pictures, they'll give better results with all pictures, even difficult ones, if you experiment and treat them as starting points for improving your photos, rather than as one-shot, take-it-or-leave-it magic wands.
Your next step, once you have a feeling for Levels, is just to jump in and edit without relying on the Auto commands. Note the Channel pulldown menu, which allows you to edit the R, G and B channels separately.Remember that you can't break a digital picture by tinkering with it, the way you could ruin a film negative – just be sure that you don't save and close it until you're completely satisfied. For extra safety, be sure you're working on a copy, not on your original. There are two areas that may cause you unnecessary concern when working on a photo.
- A JPEG is degraded to some extent every time you save and close it. Note those three words – 'save and close' because you can perform multiple actions on your image during an editing session. The resampling and compression only happens when you save and close the JPEG. If you close it without saving, nothing happens at all. The best course is to convert the JPEG to the program's native format or to TIFF.
- Moreover, the multiple undos of current-generation software give you an endless escape hatch for changes you don't like. It's a 'Get Out Of Jail Free' card you never have to give back. Even if you've saved a change, you can undo it as long as you have not closed the file.
- There is a full explanation of the whys and hows of the JPEG picture format in About JPEG. Just remember, you should always work on a copy, so if you do accidentally save and close, or close and change your mind, you've lost nothing but the few minutes it takes to make another working copy.
