Perfect Color Correction in One Step

Most books and articles on digital photo processing only give basic advice for color correction, like "use Levels" or "make an S-curve."  Let's take it one step further.

[caption id="attachment_812" align="alignnone" width="336" caption="Levels - When you move the white point and black point, it changes the histogram."][/caption]

[caption id="attachment_813" align="alignnone" width="282" caption="Curves - Another way to change the histogram. This gives you more control over the relationship between light and dark."][/caption]

Note: I don't actually use Photoshop.  Partially because I don't want to pay $700 for it.  Instead, I use a free version called GNU Image Manipulation Program, or Gimp.  You can get it here. I also use a Linux-only program called DigiKam which is similar to Aperture for Mac OS X.  But in every case, Levels and Curves work the same.

Here, we're taking a portrait photograph of the bride, bridesmaids, and flower girl from Aaron & Julia's wedding.  Note the excellent scene, composition, and lighting.  You have to start with a good original, because color correction will only take you so far.  But, the shot is slightly underexposed and the skin tones look a little pale.  This is a verdant forest filled with beautiful young women, the colors should be much richer.

Another note: This photograph was shot in raw format.  Advanced cameras will shoot in raw instead of jpeg, which stores a lot more info from the CCD (and results in a much larger file).  Since more information is stored, it gives you more flexibility for adjusting the colors.  If you shoot in jpeg, your pictures will get grainy a lot faster, leaving you less room for adjustments.  There's a big debate between raw and jpeg, and it really boils down to personal preference.

Levels

What happens when we use levels?  Before we touch anything, we see how the the picture is represented by a histogram.  This shows how much of the photograph is bright, and how much of the photograph is dark.

You can see that this is a well-exposed shot, with a lot of darks and a lot of lights.  However, the darks don't quite touch black.  It looks like the shot might have too much white, but that's just because you have a giant white wedding dress in the shot.  The most important thing is the skin tones, which are underexposed.  Let's start by lowering the white point.

The skin tones look a lot better, although the bride's dress is completely washed out and the bridesmaid's dresses are faded.  Moreover, since there's not enough black, the overall picture looks a little washed out.  Let's raise the black point.

Much better!  The photo has crisp definition, but by raising the black point the whole photo seems a little too dark again.  We can solve this problem by raising the midtones:

Better, but the skin tones still aren't warm enough.  A picture like this should be rich and golden.  Let's adjust the white balance:

Very nice, but not perfect.  The dresses are over-exposed or completely bleached out.  The skin tones are well-lit but not vibrant.  This is the limit of what can be done with the Levels tool.  Let's step up to Curves.

Curves

Here we see the histogram again, this time with a line over it.  This line can be bent and stretched any way we want.  Just like before, let's start with the highlights:

Now, the skin tones are lighter, but the dresses aren't washed out.  Note that I didn't grab the top of the graph, I dragged from a point closer to the midpoint.  This brightens the entire image and kills two birds with one stone.  Make a small adjustment with the black point and you've got perfect exposure:

But, just as before, the white balance is still off.  Luckily, there's a way of adjusting that within Curves.  Rather than just looking at the overall light and dark, we have to break the photo down into its primary colors - red, green, and blue:

First, you'll notice each color has a different histogram.  This makes sense, because there are different levels of each color in the photograph.  (Lots of red from the skin tones and the yellow bridesmaids' dresses.)  Next, notice that I've stretched the red and blue highlights just a bit, increasing the red and decreasing the blue.  This gives an overall warmer color:

And we're done.  Warm, glowing skin tones, crisp shadows, perfect exposure and color balance.  Done with only the Curves tool.  Keep reading for an explanation of why this works.

(Note: The Levels tool also splits into red, green and blue.  But when it comes to something as sensitive as skin tones, the Curves tool gives you more delicate control.)

Color Theory

In my photograph, I wanted to add an orange hue because that would make the skin tones look warmer.  Orange is made up of yellow and red.  Thus, if I increase the red and yellow in the photo, I'll get the warm orange hue I want.

The red is easy; just increase the red using the Curves tool.  I focused on the red highlights (see screenshots above) because the background forest is darker and the bridesmaids in the foreground are lighter, and I want the bridesmaids to get the orange hue, not the forest.

So, how to increase yellow if there's no yellow Curves tool?  Like this:

This color circle shows "complementary" colors.  In a photograph, if you reduce one color, it will increase the complement.  So if I reduce the blue, that increases the yellow.  Again, I focused on the highlights.  Between increasing red and decreasing blue, I get yellow.  (Note: based on the color wheel, I probably could have got the same result by leaving red alone and decreasing blue and green instead.  Aren't color wheels fun?)

Meanwhile, the Luminosity curve acts independently.  So I can have a dark picture with a warm hue, or a light picture with a warm hue.  Since all the curves are contained in the same Curves tool, I can make all the adjustments at once.

The result: perfect image correction in one step, using the Curves tool.

(Another note: At the beginning of this article I mentiond the s-curve.  This is a popular curve technique because it accents the highlights and the shadows.  Personally I find it gives too much of a "goth" appearance.  A lot of these adjustments are subjective.  I encourage you to go out and find your own artistic style.)