I use my histogram all the time... I am a very much a chimper, "chimping" is a term used for a person that is always checking out the histogram and pictures on the lcd after a photo is taken.
The goal is to have the histogram stretch from the left to the right, without spiking upwards or outwards off the histogram. I would like to write something better about this but always seem to be lacking the time to put it together... trouble is it’s a technical tool and I am not a real technical person, I am very much a right brain type of person. Anyway here is my attempt...
A histogram is a visual representation of the light in an image displayed in a chart like manner. The far left are the shadows and the far right are the highlights, the sections in between represent the varying degrees of dark and light in the mid-tones read from left (darker) to right (lighter). The spikes in the histogram represent pixels from bottom (fewer pixels) to top (more pixels).
The histogram is actually a very valuable and easy tool to use and understand once you know what it means and how to manipulate the exposure with your camera settings. The darker or more underexposed your image is the more you will see the histogram represent light on the left side of the chart. A normal exposure will show the light spreading across the histogram fairly evenly. An overexposed image will show the light pushed to the right of the histogram.
Here are some images with the corresponding histogram to help illustrate:
Granted these may not be the best examples but they do help to show how the light is represented using the histogram, the colors are also not accurate due to the process used to make the graphic.
Note the normal exposure and how the light is represented across the entire histogram, with some clipping (loss of data) of the shadows showing with peaks spiking upward and flowing off the far left and right of the chart. There is further clipping shown on the under exposed imaged with even more light falling off the left end but the colors in the sky (the mid tones) are nice and rich. The over exposed image shows lots of detail in the mid tones with some clipping (loss of data) shown by the light falling off the chart on the far right. Extremely over or under exposed images tend to be useless due to the loss of data, moderate clipping is OK and most often can be corrected depending on the format the image was shot in (jpeg vs raw) and the extent of the clipping.
A histogram does not necessarily need to be in the middle all the time, it just depends on what your scene may be. A winter scene for example may be pushed to the right of the histogram vs. a scene placed against a black or dark background which may show on your histogram pushed to the left. The challenge in extreme scenes with lots of contrast is to control the clipping that may be present, a histogram is a great tool that will allow you to make changes on the fly to your exposure, which is just one of the great things about digital photography!
These three images were actually taken this way on purpose for an HDR (high Dynamic Range) image that I created with them. The three images were combined and edited using software to create one image that would take advantage of the broad range or high dynamic range of light... but this topic is a WHOLE different post.
:-)
