In the article, Introduction to Histograms in Digital SLR Photography, we discussed what a histogram is,
Put simply, the histogram is a graphical representation of the exposure of an image. More precisely, it is a graphical representation of the tonal range of an image.
The histogram shows a set of 256 vertical bars with each bar representing a particular tonal value of grey ranging from black starting on the left side all the way to white on the right side. Each bar gives us a graphical representation of how many pixels are in the photograph for that particular tonal value.
So how can this graph help you? It helps in two ways:
- To determine if the image is properly exposed
- To determine if the image has too little or too much contrast
Histograms For Exposure
The above image is overexposed as seen by the right side clipping and the fact that the graph is heavily weighted to the right. This signifies that there are parts of the image that are too light and detail is being lost. Much of this overexposure can be seen on the hood of the car.
The above image is underexposed. This can be seen in the histogram with the left side clipping and the fact that the histogram is heavily weighted to the left. In this image, much of the underexposure is coming from the dark background as well as the back of my son’s head – you can see that part of his head gets lost in the background.
This image shows good exposure. Notice that there is no clipping and the graph is showing most of the pixels in the middle portion of the histogram and tailing off to zero at either end.
Histograms For Contrast
The other nice thing about histograms is that not only do they assist you with exposure, but they also help in gauging whether there is too much or too little contrast. It needs to be kept in mind though, that contrast tends to be more of a compositional issue and thus can be adjusted by changing the compositional elements in your photograph. In other words, if you wish to try and add contrast to a low contrast scene, very little of this can be done through adjusting exposure and instead you will likely have to change many of the compositional elements in the scene. This may involve changing your framing, changing the camera position, changing the lighting or by adding or subtracting color by way of adding or eliminating certain subjects in the scene.
Let’s explore some examples:
In the above image, you will notice in the histogram that there is no clipping. But most of the pixels are concentrated in a very narrow tonal range. This is an example of a low contrast photo. There is enough contrast in the image to make out the fact that it is sand. While a lower exposure may bring out more of the shadows and improve contrast, a larger improvement could be made (if desired) by waiting until later in the day when the sun is lower and thus creating bolder shadows throughout this scene.
The above example, shows a histogram that is relatively spread out. This pattern indicates “good” contrast.
High & Low Key
In some cases, you do not want an image with either “good” contrast or “perfect” exposure but instead you desire either a “high key” image or a “low key” image.
While the histogram is not clipped in the above image, you will notice that it is heavily concentrated towards the right (white) side which would normally indicate overexposure and low contrast. But in this case, the overexposure is intentional and is is an example of a creatively controlled “high key” image.
Here you will notice the clipping to the left which would normally indicate an underexposed image, again with low contrast. But again, this underexposure is intentional and is an example of a creatively controlled “low key” image.
Hopefully these examples will give you a better understanding as to how to read your histogram and what it can tell you about your image. It can provide you with a great tool when you are in the field allowing you to make any necessary adjustments whether they be for corrective or creative control.
If you have any further questions, don’t hesitate to contact me directly with your question!
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