Bair Art Edition's Tutorial on:
Adjusting Color & Exposure
In Adobe Photoshop
Solving Exposure Problems: Using Levels
The levels tool is a powerful way to redefine the tonal values of an image. It displays a histogram of those tonal levels. The levels tool can be found under the menu Image/ Adjustments/ Levels. Never use "Auto Levels"!!! Unless you like to gamble that much!
We will be using this same tool, but, of course, applying it as an adjustment layer. Adjustment layers are always preferred (learn more about ajustment layers).
Either go under Layer/ New Adjustment Layer/ Levels
Or on the layers palette (accessable in Window/ Layers) click on the half white & Black circle and choose "Levels"
A Histogram will show up (click here for more info on histograms and exposure). You are now ready to correct the exposure without losing any information from the file, because you are using an adjustment layer.
Correcting Flat Exposure
Some images aren't blown-out or too dark. These images have most of their value in the midtones, and only lack true highlights or shadows. This is easily fixed, and has lost the least amount of information.
Simply pull in the white and black points to the areas of the histogram where information is begining to appear. This will give the image more contrast.
I admit that I didn't pull the black point all the way to the begining of the info, but when you see the result, you might agree that I added enough black for a good contrast:
Now, you may notice that the Levels tool can be broken down into channels of Red, Green, and Blue, we'll discuss that application further in Correcting Color Balance Using levels.
Correcting Under/Over Exposure
We will only cover correcting underexposure, however, the same technique used here can be used with overexposed images, just in reverse.
In an under exposed image, the values are mostly in the Black to midtone range, and still contain most of the information, but that info is compressed. Simply take the white-point slider and clip off where there is no information.
Now I need to dodge around their eyes!
Bringing out the shadows
If the image is still too dark overall, you'll need to further bring out the shadows. To do this without destroying the highlights (as much as possible) use the mid-point and drag it towards the black point until the image obtains the correct exposure.
The image may go flat, losing much of it's contrast; this is normal, and will be fixed in the contrast/ brightness section, but you should read adding contrast using the curves tool.
What occurs when you slide the midpoint is an interpolation of the values before and after that point. You have told photoshop that everything before that mid-point is in the shadows half of the range. By compressing that space on the histogram, the software will proceed to stretch out the values, lightening them overall.
You've also told photoshop that everything beyond the midpoint is in the highlight half of the range. Since you stretched the values out by moving the mid-point, the software will compress that information so it will evenly fit in the highlight portion.
Here is an example, seeing the histogram and the image, you notice that there are already highlight values that are blown out. You don't want to totally destroy them further by clipping them off, so I pulled the mid-point over:
You may notice that I also brought up the black just a bit as well. The images look as follows:
In the next section we'll fix the contrast.
These are the other sections of this module:
- Main Exposure Page - Discusses basic exposure issues in digital images, including histograms.
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 Contrast/Brightness to Fix Exposure Corrections - Having used one of the above methods to correct exposure, the image may become flat and without contrast. This will fix it!
- 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!