The first item you should be correcting when you bring a photo into Photoshop is the tone, or the variance of dark and light, of the image. Most people do this with the Brightness/Contrast feature. Brightness increases the overall white in a photo, while contrast increases the difference between black and white. Although they may seem effective, using this old-fashioned tool lacks precision and detail, often doing more harm than good to your photo. To become a better Photoshop user you must forget the Brightness/Contrast feature and begin using the Levels adjustment instead. Master Levels and you will master the tone of your images.
What does it mean when an image is over or under-exposed? When an image is so dark that many areas contain pure black and no detail, that portion of the image is considered to be under-exposed. This means not enough light was getting through the lens to provide enough detail to the film or digital image sensor. If too much light was getting through, portions of the image may become so bright that they lose all detail and become pure white. This is called over-exposure.
Open any image and press Ctrl-L, or better yet, add a Levels Adjustment Layer. This will bring up a graph called a Histogram. It plots the brightness of an image from dark (on the left) to bright (on the right). The curve plotted along the histogram represents the strength of the tone along that scale. The higher the peak at a point along the histogram means the more information of that image resides in that level of brightness. By observing where the peaks and dips are along the histogram graph, you can get a feel for what the tone of your image is.
If your histogram leans to the left, your image has lots of shadows or black and is possibly underexposed. If your histogram leans to the right, your image has lots of highlights or whites and is possibly overexposed. Histograms that are balanced and symmetrical often stem from images that are more pleasing to the eye and are generally considered to be exposed properly. These images are often referred to as having a balanced tone. It’s not wrong to have a histogram that leans to the left or to the right, but generally creating a vivid image requires a more balanced tone.
Open the image (Correcting-Tone-Levels.jpg) in Photoshop. You can adjust Levels in two ways. The best way to make adjustments to images is through the use of Adjustment Layers. Otherwise, the old-fashioned way can be found in the Image menu under Adjustments or by pressing Ctrl-L.
This image of the Genesee Gorge at Letchworth State Park lacks contrast and it is a little under exposed. It was taken in bright sunny conditions and I suspect the camera sensor got confused by reflections. It’s not a great photo. The tone is muted. Let’s take a look at the Histogram in the Levels adjustment.
Take note of the following controls and how they work:
What does this histogram tell me?
The first thing you need to do when you bring up Levels, is to study the histogram to find out what the issues are, and then adjust your sliders to their optimal positions. In this example the far left side of the histogram is lacking information (no black graph). This means that there are no deep shadows in this photo. It is a daylight photo of an open canyon, so there shouldn’t be overly strong shadows, but there should be some mild shadows within the trees.You can almost tell by looking at it: the darkest points in the image only reach a mild grayish green. They should be darker.
On the far right, a thinning graph shows that there are some highlights, but not many and certainly not approaching pure white. Looking at the image, the frothy water, as well as the reflections from wet surfaces, should be pretty close to pure white on a bright sunny day. They aren’t.
Luckily it appears as though almost no histogram information is being clipped off the far ends of the graph. If too much information was clipped off the far ends, it would be very difficult to fix. Any information that is clipped from the graph, cannot be recovered.
Essentially what you need to do is tell Photoshop that you want the image’s darkest shades (on the far left of the graph) to be close to the black point, and the image’s lightest shades (the far right) to become close to pure white. This will re-map all the shades in the image, giving it better contrast, detail, and making the image more vibrant.
Not every scene you capture needs to have pure white and pure black in it. A night scene for example, probably won’t benefit from having pure white remapped in it, because pure white in a dark scene is unnatural.
Levels has an AUTO feature. But I highly recommend never using it. It tends to change the color, which is never something you want to do in the Levels Adjustment. More importantly, it does not consider the conditions the photo was taken in. So if you are trying it on a photo of a dark sunset scene, for example, it may brighten the image too much and change the warm colors to a balanced tone. Once you get used to manipulating the sliders, manually adjusting Levels shouldn’t take much more time than hitting the “Auto” button.