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Bair Art Edition's Tutorial on:
Adjusting Color & Exposure
In Adobe Photoshop
Solving Exposure Problems:
Using Curves For Contrast
The last module discussed why and when an increase in contrast is needed, this module explores how curves allows for better, more precise, and more "lossless" adjustment to contrast.
Curves is not available in Photoshop Elements, so Contrast/Brightness would be the default method in that case. And still, some find curves confusing and difficult compared to the linear sliders of Levels and Contrast/Brightness. For most applications, curves will give you better results, but the linear tools will also give you easier, acceptable results.
For basic use and definition of this tool, read Using Curves to Correct Exposure.
First lets see how the Contrast/ Brightness compresses the values in order to create that depth. We'll use a curves graph to simulate this compression.
Of course this is exaggerated for demonstrative effect
You can see that as the slope is increased in order to make the lights lighter and the darks darker, values are lost as many areas turn completely white or black (these areas are flat against the top and bottom). This linear scale dangerously loses values.
Curves can be used to compress the values as well, without completely clipping off information. The method is a non-linear "bending" the information. Again the curve is exaggerated to demonstrate the difference
You can see that the values are "bent" in order to compress them, but no values are completely lost into the shadows or highlights. A contrast curve always takes on a typical "s" shape.
A realistic curve is only bent to this degree:
This is only a very subtle curve, and that is best. A little goes a long way.
Here is the before and after applying the curve:
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Before
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After
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These are the other sections of this module:
- Main Exposure Page - Discusses basic exposure issues in digital images, including histograms.
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Using Levels to Correct Exposure - Covers the power of levels as an adjustment layer to correct underexposed and slightly over exposed images. This is my favorite method.
- Using Curves to Correct Exposure - This method is favored by many who like te freedom to move the adjustment in all directions. (I like the controlled, linear levels, but then again I'm not that artsy). It is also most powerful in lightning/darkening only certain ranges (highlights, midtones, or shadows).
- Using Curves to Add Contrast - A better, more controlled approach to adding contrast. It "pinches" shadows and highlights rather than clipping off information.
- Dodging and Burning - There are many known ways to do this in photoshop, including using the tool of the same name. However, we won't discuss that tool, we'll be using a more powerful method that involves layers. This allows it to be turned up or down and on or off!
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- Stephen Bair, Utah Wedding Photographer, Bountiful Utah Wedding Photographers
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© 2008 Masterlab
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