If you have a digital camera or a program for editing photos, you will certainly stumble in a histogram, which is a graphical representation that allows you to precisely check certain key aspects, such as exposure or tonal range.
Reading the histogram of the images is useful at the time of shooting but it is also essential during post-production. All SLRs and compact cameras allow you to view the histogram at the time of shooting or playback of the newly captured image. This helps you in a simple and precise way to understand if you have cut some details because it is too dark or too light.
Shooting in RAW format and working in post-production, you can recover a lot but you cannot perform miracles. For this reason, it is essential to properly expose a photograph already at the time of shooting.
When you start taking pictures, especially if you are photographing digitally, you have to consider two fulcrum points. The difference between the darkest point and the lightest point in the image may exceed the limits of your camera. There are scenes that by their very nature will favor a predominance of dark pixels and others where the photo has a predominance of bright pixels;
Histogram photography
Observe the histogram and make sure that the curve of the graph does not seem to overlap on the left or right edge of the frame. The histogram makes you understand with certainty that the photo has some areas of shadow too marked because the histogram is not simply moved to the left, but literally splits on the left edge of the limits of the histogram. This is what you have to pay attention to and notice when you take the picture.
If you decide to take a photograph in a dark room, without flash, with low ISO, your histogram will inevitably be all moved to the left, because obviously you have a net prevalence of dark tones. If, on the other hand, you point your car straight up against the sun, it is obvious that the histogram of your camera squirts all to the right.
What does this suggest to you? It is simple: the histogram is your guru for the show.
It is reading those curves and those diagrams that you can know if your photograph is underexposed, overexposed or if, instead, you have centered the right exposure. Do you agree with me that this is a crazy tool, a real irreplaceable guide for our shots? I am sure that from now on you will look with a different eye that beautiful system of curves and lines that until now has intrigued you but did not conquer you but, moreover, you are here to learn how to use your car.
Range (tonal and dynamic)
With Tonal Range we refer to the amplitude of color nuances present in a photograph, while with Dynamic Range refers to the brightness levels reproduced by the camera sensor. Generally, but it is not a rule, we tend to maximize the value of gamma, going to get images with wide tone from deep black to white (avoiding absolute white). The image with little tonal range is substantially flat, with little contrast between light and dark areas. Hover over the image below to check the change.
Both the dynamic range and the tonal range can be divided into zones refer to a specific area of histogram photography. To refer to these subdivisions, the terms shadows, half tones and highlights are used. It is easy to understand that the dark areas will be the shadows, the bright ones the highlights and everything else will be confined in half-tones. Precisely for this reason the half tones are used to have the greatest tonal range, counting the most information in our photography.
Underexposure or overexposure?
The main function of the histogram is to provide us with an exact reading on the exposure of the photograph. It represents, through a statistical distribution, the brightness of the photo or, better, the number of pixels related to each tonal value.
The understanding of this tool is very simple. Along the horizontal axis we find the values relating to shadows, half-tones and highlights (from left to right). On the extreme, left we will find the value of the perfect black (RGB 0,0,0), on the extreme right instead the perfect white (RGB 255,255,255). If the highest part of the graph will be inside the light zone we will have a very bright photograph, and vice versa.
Like every histogram, the graph is constructed with a series of close columns, each of which represents a precise tonal range value. Absolute black and white are found at the ends and it is important that the respective columns are kept to a minimum because otherwise it will mean that there will be burned areas, flat and without detail. There are particular cases in which this result is aimed precisely but, in general, there should be no closed shadows or burned lights in the photographs.
These phenomena are called Clipping, that is when in a histogram there are some pixels that resides in column 0 (black) or 255 (white). For each image you can create different type histograms, as well as the color value of a pixel can be measured in different ways.
RGB histogram photography: This is the classic histogram that is displayed by most post-production programs. It is not high that the histogram that is formed by the overlapping of the Red, Green and Blue channels.
Brightness histogram: Represents the perceived brightness and even if based on the three RGB colors they are calculated with a weighted average (they do not have the same weight). It is precisely associated with a weight of 59% green, 30% red and finally 11% blue.
Color histogram photography: Shows the representation of primary colors (RGB) and secondary colors (overlapping of two or more primaries). The set of all colors is represented by the gray area. This particular histogram is also used by Lightroom.