The histogram is a graphical representation by bars of the gray tones of a photograph, basically it is about representing the frequency with which a tone is repeated
This famous graph has two axes, one vertical and the other horizontal. The important thing is that you remember that each axis indicates:
- The vertical axis tells us the number of pixels of each tone, that is, the higher the bar, the more tones like that there will be in the photograph.
- The horizontal axis indicates the different shades of gray there are. On the left side is pure black and on the right side of the horizontal axis pure white, in between you will find shades of gray or light.
As you will understand, the further to the left are all the bars or “mountains” the photo will be darker, with many shadows. If, on the other hand, the histogram tends to the right, the image will have many more white tones, therefore it represents an image with a lot of light.
These values also represent the amount of basic colors there are (red, green and yellow), it is a matter of selecting one histogram or another. We will focus on the lightness or gray tones histogram.
Are there perfect histograms?
Once we know how the dark and light tones are represented, we can conclude that a “correct” histogram would have information in all tones, that is, it would have a bar for each tone and the appearance of its graph will be of frequency uniform.
But BEWARE, a uniform graph does not have to be correct, the values will help you get an idea of how the light is distributed in the photograph and how to improve it, but it is not an official guide to take good photos.
It all depends on the result you are looking for , if you take a high-key photograph like the one in the example, the graph will not be uniform at all and it will still be correct, since it fits my result.
In a night photograph, the curves will tend to be in the left area, since the image is dark in itself and for that reason it is not incorrect, do you understand it?
Now, if the histogram is not a guide which must be followed as if it were the civil code, what are histograms really good for? Let’s see.
How can it help you
Once you know that the lights (white) are represented in the right part of the graph and the shadows (black) in the left part, you can “read” your photo without looking at how it has been on the LCD screen.
The LCD screen is not 100% reliable , since the external light it reflects affects it directly, also the brightness you have configured or the angle from which you look at it, therefore, using these brightness bars is the most reliable means to ensure that your photograph is correctly exposed and it is highly recommended that you start using it.
Learn to interpret it
Take a look at these examples to understand it better.
Look at the histogram of this photograph that I took in Asturias, at the time of taking I was guided by the values to make sure that the lights were not burned out and thus recover the maximum possible information from the sky and the water when developing in Lightroom .
As the objective was to achieve an underexposed image, where the dim lights were the protagonists, its histogram tends to the left, where the blacks are.
You can see how there are many areas with pure black by looking at the peak on the left, while on the right side, the white area, there are many fewer pixels.
Does the example have a correct histogram? Well, as I explained before, yes, because I have achieved the result I was looking for even with a too underexposed histogram.
I give you another example: look at this diagram, at a glance without having checked the photograph on the camera screen you can get an idea of what it will be like.
It’s backlighting, so we’ll have a lot of pure blacks, hence that pixel spike on the left side of the histogram, but as for the highlights, I didn’t want an overexposed environment, if not a photograph rich in shades of gray, like a gradient from black to white, so you can see in the graph how there is information in almost all shades of gray to white.
In this photograph, if I had overexposed the lights (a peak on the right side of the graph), I would not have achieved that melancholic atmosphere, it was a great help to guide me through the histogram.
In what situations should you use it
In the field, as much as you know how it works, you will also have to practice using it, since many times we do not use this type of function due to laziness or because we believe that what the camera screen shows is the correct thing, but you have already seen which is not so.
Imagine that you are in front of this Portuguese landscape and you take this same photo, the normal thing is that you immediately look at the LCD screen to check the result. If you have low brightness you may see it correctly or you may think it is a good shot.
Now look at your graph, do you see the pixel peak on the right side? It means that there is too much light , the values are warning you that there are burned, overexposed areas , information that you will not be able to recover in Lightroom, Photoshop or the program you use, even if you have shot in RAW .
Sure you can identify the areas of the sky that are badly exposed, to correct it as you already know, we would simply have to close the shutter, increase the shutter speed or reduce the ISO sensitivity according to each situation, but of course, this can only be done at the moment of the shot, if you go home thinking you have the correct photo for not looking at the histogram …
A few quick tips before proceeding:
- To expose correctly, I recommend using spot metering to take as a reference the areas most prone to overexposure.
- Look in your manual for how to disassociate the focus button from the exposure , so as not to change the exposure each time you press the focus button.
- The data you see on the screen is based on the Jpg file, so if you have touched these settings you should take it into account. You can take a look at the RAW vs JPG article to read more about this.
Do you understand now the importance of using it? Imagine a portrait photograph with overexposed skin, we would lose information on the skin, pores, makeup, beauty, color, etc., a true catastrophe.
How to activate the data in the camera
This option is usually disabled, I suppose so as not to scare first-time starters with weird graphics. It is best that you look in the instruction manual of your camera how to activate it, since each model may be different:
- In the vast majority of Canon cameras, it is activated by entering the preview of the photographs and pressing the “Info” button, each time you press it the screen will change to show more or less information about the image.
- In Nikon cameras you will normally have to access the menu and look for “playback display options” and check the “Histogram” option.
If you activate Live View mode and press the “Info” button in the case of Canon, you will see the bars in real time, a good trick for many situations, especially when recording video with the SLR camera.
How to activate the histogram in Photoshop
To see the histogram of an image in Photoshop, simply open the image, go to the top menu and look for Window -> Histogram.
It will now appear in the floating menu. If you look at the upper part of the graph there is an option called “Channel”, by displaying it you will be able to choose between seeing the Brightness or basic colors (Red, green and blue).
Show it in Lightroom
In Lightroom you won’t have a problem because it appears by default on the right side of the image. It works in the same way as the camera histograms and it is important that you keep it in mind while editing a photograph so as not to burn out lights.
As with the camera’s LCD screen, your monitor may not be calibrated correctly and what appears to the naked eye to be a well-exposed image may actually have burned areas. Having a properly calibrated monitor is highly recommended, since the final result of our image depends on it, we will talk about it in another article and about one of the most famous calibrators, the X-Rite i1 Display Pro.
There is a trick for Lightroom to warn you of the areas that you should correct (as long as your purpose is not to leave it like that). Simply activate the buttons at the top of the graph and the burned or underexposed areas will be colored red. So as you modify the settings, the program will warn you through the frequencies if you spend adding light to the image or underexposing areas.
- Remember that it is not about looking for the perfect histograms , but about using them to get the photo that best suits what you are looking for and thinking about post-processing.
- The overexposed or very underexposed areas are irrecoverable even if we are shooting in RAW .
- Get used to being guided by the frequencies of the camera diagram and not just by the display.
- Take the same photograph by changing the settings like ISO or aperture and compare the histograms to really understand how it affects the final result.
- Use Live View mode to see changes to the graph in real time.