The Perils of Photoshop’s Brightness/Contrast Command
I often tell students in my Photoshop classes that it is never a good idea to use the Brightness/Contrast command in Photoshop to adjust the brightness or contrast of a picture. But why not? Why would they have a command called Brightness/Contrast if you should never use it? Hopefully, this explanation will clarify the specific perils.
Caveat for Adobe Photoshop CS3 users: Could it be? The Brightness/Contrast was changed in Photoshop CS3 and has been vastly improved so as to be mildly decent. If you use Photoshop CS3 and want to see the ugliness dicsussed in this tutorial, click the Use Legacy checkbox in the Brightness/Contrast dialog box. I would still maintain that properly using Levels (or better yet, Curves) is still preferable to Brightness/Contrast. Okay, carry on.
We'll use a bad photo from my digital camera as an example. The picture below is a bit on the dark side. You can compare the results I achieved with the Brightness/Contrast and Levels adjustment layers by moving your cursor over the links to the left of the image.
Why Brightness/Contrast stinks
So why is Brightness/Contrast no good? In short, it is no good because it overcompensates. You see it is a universally accepted tenet of imagery that contrast is good. When your picture has good contrast, the darkest parts of the image are really dark and the brightest parts are really bright. that that a good image
When I tried Brightness/Contrast, I used these settings...
Since the original picture was too dark, I increased the brightness to compensatebut in doing so, it brightens everything., everything became more pale. To restore the darkness to the darker areas like the background stage area, I increased the contrast.
One drawback to using Brightness/Contrast
is that the image seems to lose pixel details in the highlight and
shadow areas. For example, in the first picture, while it
is a little dark, you can see shirt folds on the yellow shirt on
the left. The second Brightness/Contrast adjusted picture, while
brighter, loses detail in the yellow shirt highlights. The detail
has been washed out by overcompensated highlights. (The same can
also happen with shadows)
Now you may be thinking, "Ah, but isn't that why they added the Contrast slider? Doesn't that take care of the problem?"
Unfortunately, the Contrast slider also makes global adjustments to shades you don't want to affect... using the contrast slider basically edits the Bell curve all at once, flattening it or spiking it. Remember how I said that having all your grays at shade #128 would be "balanced" but lack contrast? Well that's exactly what the contrast slider does when it lowers contrast, it makes all the pixels closer to middle gray, causing a spike in the bell curve at value #128. It reduces the distance from the middle gray that the shades go, and pixel information is lost.
When you increase the contrast with the Contrast slider, it pushes all shades away from the middle gray value, brightening the brights and darkening the darks simultaneously. But you likely need the middle level grays, and you may not want to polarize the darks and lights simultaneously. It will flatten and even invert out Bell curve if we let it. Once again, the Contrast slider is changing more than it should.
One tool that gives you more control is a Levels adjustment layer. The original is first, the B/C version second, and third is the Levels adjusted version.
Levels adjustments allow you to isolate the area of the curve you want to change... the lights, the shadows, or the midtones. That's why they're better. With a levels adjustment, you can brighten the picture's middle tones without seeming to place a pale film over the deep dark shadows. Your range can still start at Shade #8 and go up to Shade #246. The same principles apply to color images as to the grayscale images regarding the B/C sliders... it's just that there are multiple color channels instead of just one. Not only can we see the wrinkles in the highlight of the yellow shirt, but we can even see the stripes better on the sweater on the right!
I used these settings...
We go into even more detail in the Color Correction & Printing class about how to adjust images without losing contrast. Using Levels correctly will achieve more brightness without having to polarize the contrast range.