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Four curiosities about the histogram

Four curiosities about the histogram
Four curiosities about the histogram

At this stage of the game we should all know that the histogram is the best friend we can have to evaluate the exposure of a photograph. Surely we know how to interpret most of the forms that the graphic can take, but today we are going to discover some aspects that we probably do not know about the histogram.

Digital photography has a perfect ally, the histogram. If we know how to master it and interpret it, we will rarely have exposure problems when shooting. And what is more important, it will also help us to control the development of our development from start to finish. The only thing we have to do is to know the signs to know how to act when we see it. It will make the difference between perfect photos from the technical point of view.

Some of the curiosities are sure to dominate all readers of this blog, after so many years writing about its benefits, but some will only be recognized by the most experts in the field. And I hope you all get at least one new idea about the histogram.

As always we will look for a good definition to know exactly what we are talking about. The histogram is nothing more than the graphic representation of the frequency of appearance of certain values. It has multiple applications. If we focus on photography, which is what we are most interested in:

A photographic histogram has a horizontal axis in which the luminosities that go from black to white and a vertical axis that shows the number of pixels in percentage with respect to the most repeated of all are represented.

And now let’s look at some of the things we can discover just by looking at a histogram. It has many more things than we think.

The histogram is a summary

As we have pointed out above, the histogram represents on the horizontal axis the luminosities that go from absolute black to absolute white, passing through a series of grays. Well, if we had patience, we would count up to 256 levels from the darkest area to the brightest one. And it would only be true to reality if we were working with a jpeg, which effectively has those levels.

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There is everything

What if we work with a RAW ? We know that it does not have so few levels. They are 16 bits deep , and if the calculations do not fail us, they represent 65,536 levels in total. There is no screen in the world that is capable of representing such a quantity of information, so it was decided to summarize it in just 256 levels of the compressed format. If you want to see a real histogram of a RAW file, you can do it here.

There is always an inbound and an outbound histogram

When we take a picture, the histogram has an appearance. As we have seen, it is nothing more than a summary of all the information that a RAWcan capture and we can not forget that it is an interpretation of the file. What we see on the camera screen is the histogram of the jpeg file. Never from a gross file. We can not trust our camera.

But what we can not forget is that when we reveal the image in any image editor we are creating a new one with a different distribution of the luminosity values. In some extreme cases, it will be completely different because we wanted to avoid excessive contrast or expand the dynamic range of the image. It’s the exit histogram.

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Input histogram

In my case, I am a strong advocate of exposing the right. My photos always seem brighter than they really are. Then they have nothing to do after analyzing the input histogram and converting it into the output histogram due to the bad art of the development. One does not justify the other. In the first, only the area of ​​the lights is important; and in the second one, we must assess from the darkest shadows to the brightest whites. And never think that there is a single ideal histogram…

The histogram reveals the dominant color of the photograph

I always say in my classes that, in a bar bet, you can always win if someone challenges you to discover which is the dominant color of a photograph. And you can discover it just by looking at the area of ​​the lights, the right side.

When you see the input histogram in Adobe Camera RAW, always look at the color that sticks out at the far right. That, and only that, will be the dominant color of the photograph in question. And there is no doubt. It’s that simple. Even if it is only a point of color on the X axis of the histogram.

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I see warm tones

Then we will have to correct or adjust the dominant with any of the tools we have at our disposal. Next time do the test and you will see that it is true. This can be even easier, even if you are working with the screen of a laptop, to solve this problem manually, only with the Temperature and Tint parameters .

The underexposure that we see in the histogram can really be a saturation problem

This case surely you have lived on many occasions. The histogram rises vertiginously on the Y axis in the value 0. Neither short nor lazy we begin to manipulate the parameters Black and Shadows… And everything remains the same. That bar does not go down and if we work with the threshold level we always see that area marked.

That is one of the signs to discover that we are really not facing a problem of underexposure, but of saturation. The last test that needs to be done is to change the Color Space (if we are working in Adobe Camera RAW ) in Workflow Options. If we go from Adobe RGB to Prophoto and that problem disappears, the histogram is telling us something else.

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In Lightroom you can also do

The space of color influences and much in the exhibition , by the different capacity to represent the colors. And if the level 0 of the histogram goes up a lot, it’s because there is a color that it can not represent. And the solution is very simple. It is not necessary to change this space, but to lower the Saturation of said color with the help of the Destination Adjust tool in the HSL tab . With desaturating that color that gives us so many headaches, we will make it fit within the space that we have by default. And by the way we will not leave the flat image without shadows.

I hope these curiosities are useful to you and you can take advantage of them in your future work. Do you know any more curiosity that you want to share with all the readers? The histogram, as you can see, is fundamental for digital photography.


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