When taking a photo, your camera records the different areas of light. These areas or tones of light vary from light tones to dark tones. The tool that allows you to visualize the tonal ranges of the image is called the histogram. In this article we will see what a histogram is, what it is used for and how to use it.
What is the histogram and how to use it?
The histogram allows you to visualize the distribution of pixels that make up your image. These pixels are organized according to their brightness. In other words, it is a graphical representation of the distribution of light intensity of pixels in your photo. This is one of the great advantages of digital photography compared to film photography. With just a glance, this tool lets you know whether the exposure of your image is correct or not.
It is therefore the ratio between the number of pixels (vertical plane) and the brightness (horizontal plane) defined by the different tonal ranges of your photo. This tool will be useful in two cases: for shooting and for retouching (Lightroom, Photoshop, etc.). On most cameras, you simply press the INFO or DISPLAY button to display the histogram. On hybrid cameras, the histogram is displayed when taking a photo, whereas on most SLRs, it is only displayed in playback mode, that is to say when the photo is taken.
How to use the histogram in photography
Graphical representation of the distribution of pixel light intensity in your photo.
To the left of the histogram, you have blacks (dark tones).
In the center of the histogram, you have the midtones.
To the right of the histogram, you have the whites (the light tones).
In other words, the histogram is a graph that gives you the distribution of the quantity and intensity of light in your photo. The higher the graphic representation, the more information you will have in the scale of light tones. Conversely, the lower the graph, the less information you will have about these tones.
Be careful, however, not to have a peak that protrudes from the graph, because this means that there is underexposure or overexposure depending on the position of the peak. This results in a loss of information in low or high lights. Conversely, if the peak is too low, this means that there are no or few pixels and brightness in the low or high lights.
Therefore, the histogram also tells you if there is a loss of information. This lost information cannot therefore be used on the editing software. Try to maximize the amount of information in your image when shooting.
The idea is to obtain maximum detail in the photo and thus avoid blocked pixels or burnt pixels. A blocked pixel is a completely black pixel. There is no more light information inside.
Conversely, a burned pixel is a completely white pixel. There is no longer any light intensity inside. Pay attention to both ends of the curve and look for blocked pixels and/or burnt pixels. For a well-exposed Jpeg photo, the histogram will stop just short of the right edge. For a photo in Raw format, the histogram will go to the right edge, but not beyond. Prevention is better than cure.
The ideal histogram does not exist!
The perfect histogram does not exist just like the perfect exposure does not exist. It essentially depends on the light levels (which are different from one shot to another) and also on your artistic approach. For example, if you want to do low key (underexposure) or high key (overexposure), then do not take the histogram into account. Just make sure you have the information you need to develop your image.
For example, a photo of a landscape under the snow will give a histogram which will show an overexposed photo, due to the light tones of the snow. That said, if the exhibition suits you, then great!
Misleading screen
The screen of your device can mislead you about the exposure of your photo. Indeed, depending on the brightness of the screen and where you are (indoor or outdoor, in direct sunlight), the rendering on the screen will not be faithful to the exact exposure of your image.
The histogram will always be faithful to the exposure parameters, whatever the shooting conditions.
Try to have a uniform distribution across the entire graph by playing with the exposure parameters and thus obtain a “balanced” image. The ideal is to have a histogram that is located more in the center of the frame, without extending too far to the left or too far to the right. The number one enemy in digital photography being overexposure, it is better to have a curve located too far to the left, in the low lights, than too far to the right in the highlights. It will be easier for you to correct dark tones during post-processing.
The histogram in practice
Take your photo by choosing your exposure parameters: aperture/speed pair, manual, etc.
View and view the histogram on your device screen.
If the histogram extends beyond the left side of the frame, then overexpose (slightly).
If the histogram extends beyond the right side of the frame, then underexpose (gradually).
When the histogram overflows on both sides, then underexpose to bring the right curve back into the frame.
Shoot and check again… and usually, it’s all good!
HISTOGRAM – sum up
The histogram is the graphic representation of the exposure of your photo.
Quickly see if the exposure is correct or not (blocked pixels or burnt pixels).
Left side: dark tones.
Right side: light tones.
Retouching assistance (RAW format) to correct exposure.
I hope this article will help you better understand the benefit of using the histogram.