This photo shows a subject with average brightness. The photo is well exposed histogram, as expected, is relatively centered; the tonal range goes from black to white, but the majority of the image is composed by midtones. This is not an easy subject to expose - it is enough to overexpose or underexpose by 1 stop to lose some detail in the black or in the withes. Here, instead, the graph is close to to both the sides, but it does not touch any of them.

This is a completely overexposed photo. The dark areas are recorded as midtones, and the highlights are so overexposed that they have become a white area, without detail. The histogram, clipped on the right side, shows the loss of image data: this photo can not be recovered. If you get an histogram like that, set the exposure compensation a negative value (e.g. -1) and repeat the photo. If the dynamic range of the camera is not enough to record the scene, you have to use special techniques as blening exposures with Layers and Layer Mask.

This photo has two main areas, a very dark one and a midtone area; there are very few intermediate values between the teo areas. The dark area is very close to the black side, but it is not clipped; the second, lower, peak of the graph represent the sky and the other midtones area of the photo. This is the correct exposure when you want to create a kind of "siliouette".

This is the classic "layer" image. In the histogram, there are four main peacks that represents the four layers of the photo; each layer has a slightly different brightness. Other than that, the histogram has a lot of empty room on both sides: it mean that the photo has low contrast. It would be pretty easy to increase the contrast with PS by dragging the white and the black point to the edges of the histogram, but here I preferred to mantain the low constrast of the scene, to create a soft, relaxing mood.

This photo is taken during the night: the light on the landscape is the Moon light, not the Sun. It would have been very easy to get a brighter photo, but the scene was dark so I preferred to preserve the original darkness. The histogram is on the dark side, and here it means that the photo is correcly exposed, since it shows that a dark scene was recorded as dark tones.

In this photo, I set the exposure to get the Great White Heron properly exposed: the exposure compensation was set on -1. If I had used the defaul exposure, the background would be brighter, but the white feathers of the bird would be overexposed. Here, instead, the background is almost completely back (some areas are actually pure black, as you can see by the histogram clipped on the dark side), but the subject is properly exposed. When you have a scene like this one, don't worry about the clipped blacks; you have to expose for the subject.

During my workshops, I'm often asked if a peak like this one represents a bad exposure. The answer is no: this photo is well exposed. You have to worry only when the graph is clipped on the sides; if it is clipped on the top, it just mean that the large majority of the photo has a certain level of brightness, and the peak would be too high to be displayed entirey in the small histogram window. In this case, the majority of the photo is constituted by light midtones.

This is a clearly underexposed photo. When you get an histogram like that, it mean that the photo is very underexposed, unless you are photographing a very dark subject. Here, instead, the butterfly and the leaves were midtones, but they had been recorded as dark tones. It is still possible to recover the exposure, since the histogram is not clipped, but you would increase a lot the noise: in these situations, if it is possible, I recommend to set the exposure compensation on a positive value and to repeat the photo.

This photo looks "muddy" and flat because it lacks of contrast. The exposure is not bad - in these situations, you can do nothing to enhace the photo in-camera, you have to adjust the image with Photoshop, by dragging the white and black points close to the edges of the histogram, "trimming" the empty areas. It is easy to get histograms with empty areas (= lack of contrast) in foggy days, or when you photograph a subject in shade or soft light. By increasing the contrast with PS you get excellent colors and perfect exposure.

This photo has a wide tonal range, from pure black to almost white, so the histogram is spread on the entire graph. Note that the biggest peack of the histogram represents the dark blue sky, not the mountain - the black silouette is a completely black (clipped) area, and it is represented by the thin and high peack on that is clipped the left side. This is the correct exposure to get the mountain as a silouette; if you want to get some detail in the foreound in such contrasted scenes, instaed, you have to use the blended exposures technique.

This photo is overexposed because the midtones of the subject had been recorded as light tones, but it can be easily rescued with Photoshop, since the histogram is not clipped. Actually, this exposure could be considered the "perfect exposure" for this subject - it is the brightest exposure that you can get without clipping the highlight. By correcting it with PS, you get less noise and more dynamic range than a photo that has been already "exposed properly" in-camera.

This photo, instead, is too overexposed to be corrected with PS. The pink petals of the flowers have become completely white, without detail. The histogram shows clearly the overexposure, since it is clipped on the right side (highlights). In the Highlights screen, the petals would blink as overexposed areas.

You have to set the exposure compensation on a negative values and to repeat the photo.

This photo is exposed properly, since the bright subject (a white bird against a light grey background) has been recorded as light tones.

The high peack represents the uniform background; as already said, it is not a problem if the histogram is clipped on the top, while it would be a prolem if it was clipped on the left or right side.