NOTE: This article is for older versions of Photoshop
(prior to CS6/CC), but the fundamentals still apply.
Hello again, fellow photographers and Photoshop-people!
In the last article, I talked about the purpose of Curves in Photoshop, as well as where to find Curves,
how Curves works, and an explanation of some of the features. In this article, I’ll talk about how to adjust
contrast, brightness and color using Curves, and show you some real-world examples.
To Adjust Contrast/Brightness:
The easiest way to increase contrast is to create a gentle “S” shaped curve in the RGB Channel, similar to the middle diagram above. This generally consists of a Midtone point on the Baseline, with a Three-Quarter Tone point below the Baseline and a Quarter Tone point above the Baseline.
You can also give a slight increase in overall brightness by “bumping” a midtone point above the baseline (see 1st diagram), and conversely decrease the overall brightness by “bumping” a midtone point below the baseline (see 3rd diagram).
As you can see, the possibilities are endless, and can be overwhelming. Variations include:
1. Opening up (lightening) the shadows only: Move just the point closest to the “dark pixels” (Three-Quarter tone) above the baseline, leaving the others alone.
2. Bringing down (darkening) the Highlights only: Move just the point closest to the “light pixels” (Quarter tone) below the baseline, leaving the others alone.
This procedure is similar to Levels:
1. Click on the Drop-Down Menu, and pick the Color Channel you desire to add or subtract.
2. Use Points to correct your color: As an example, you want to add Yellow to offset a Blue bias to your image. Pick the “Blue” Channel (the opposite of Yellow) from the Drop-Down Menu, add points at the desired location, then move your points below the baseline to correct.
Here’s another example of where Curves differ from Levels: Let’s say that you have a Blue bias in your “Shadows” area of your image that you want to correct–the rest of the image looks great. With curves, you have the option of correcting the blue bias in the “Shadows” by moving a point down below the baseline in the shadows area only in your “Blue” Channel Curve. To keep the rest of the curve from moving (midtones and highlights), simply set “anchor” points where needed.
Here are two “real-life” examples of how to use Curves, followed by commentary as to what was done and why….
This “tiger” example is a correction for Contrast only: The uncorrected image is dark and lacking in contrast; it needs some extra “snap”, which is reflected in the histogram superimposed behind the curve (almost no “light” pixels).
The corrected image shows noticeable improvement in contrast and brightness. This was accomplished by creating a simple “S” curve in the RGB Channel, with a little extra increase in brightness in the midtones.
This “plant” example below is a correction for Color only:
The uncorrected image needs to be warmed up–the color bias is too Blue/Cyan.
The corrected image looks like the sun is shining on it. This is accomplished by adding Red and Yellow overall.
Until next month, Have Fun!!!
by John Watts