Sometimes photographers will deliberately underexpose or overexpose their photographs to create a desired effect. However, other times an otherwise good photo will have been ruined by improper exposure. This guide will walk you through the process of correcting incorrect exposure levels with Photoshop.
Things You Will NeedPhotoshop (I use CS4 but any version should be fine)
Underexposed PhotosCorrecting an underexposed image only takes a few quick steps. However, you may find yourself tweaking and adjusting the photo until you have the exact exposure that you want.
At this point you should have a nicely lit up image. However, as a result of correcting the exposure, you'll notice two problems. The first problem is that, as we can now properly see the image, we can notice that the photo has grainy elements on the left-hand side. The second is that the image is slightly too warm (it has a yellowish tinge).
For the graininess we're just going to use a quick fix to make it unnoticeable. Select the Blur tool with a medium size brush and set it to a low opacity (around 25%). Carefully blur all the graininess out of the image, taking care not to blur other parts of the photo. You may have to care over certain areas more than once. You'll notice that this isn't a perfect fix, but for this photo we only want to make sure that the viewer's eyes aren't immediately bothered by the large grainy patches.
For the second part, we're simply going to add another adjustment layer: a Photo Filter (Layer>New Adjustment Layer>Photo Filter). In the Photo Filter select a Cooling Filter and adjust the Density level until the image looks right. I chose a Density level of 10%.
At this point you should look over the image for any final adjustments you want to make. I ran over the soldier's bodies with the Dodge tool (set to Midtones, 14% Exposure) to brighten their features a bit more. You should now have a perfect image that you created out of a barely visible photo!
Overexposed PhotosFor images that are overexposed, we're going to try a different method.
"Shyleigh & Penny 1/2" by user shouldbecleaning from Flickr. Original URL http://www.flickr.com/photos/shouldbecleaning/155562895/
To adjust the levels, we're going to drag the midtones slider (the gray one) and start dragging it toward the right. You should now start to see color and contrast appear in the image. Be careful not to drag the slider too far to the right. When you reach the desired point, simply let go of the slider and you're done.
You can also use this method in reverse for underexposed images. Remember to always use adjustment layers instead of altering the layers themselves. This way you can always go back and alter the image without losing the original values.