How to read a histogram and when to be afraid of overexposure? What is a histogram? Histogram in photography: how to use? Mishima histogram

Digital technologies make the work of a photographer much more efficient and faster. Today, digital cameras can not only show the result of shooting immediately on the camera display, but also analyze these photos - show overexposed areas of the frame and a histogram (general and separate for each of the three RGB channels).

The histogram allows the photographer to analyze the frame and make adjustments to the shot instantly. And thereby save you from unnecessary processing in the RAW converter and Photoshop.

is a graphical representation of the distribution of halftones in a photograph. The brightness scale goes horizontally, and the relative number of pixels with a given brightness goes vertically.

The histogram is read from left to right, from black to white.

Look at the following examples and you will understand how to read a histogram.

The histogram shows that there are no completely black areas in the photo. On the right you can see that there are small overexposed areas in the photo.

The histogram as a whole is distributed evenly over the entire brightness range. There are small zones of over- and underlight, but they are not critical.

The following example shows how to see under- and overexposure from the histogram.

The display will not make it clear how white the background is. The histogram shows a complete dip on the laptop screen, light gray body tones and a white background around the object.

Looking at the camera screen, it is difficult to understand whether there are losses on the body of the car. The histogram clearly shows that there are no absolutely black areas, but overexposure is clearly visible on white objects.

The histogram also helps with processing in Photoshop in the Levels mode. See how the histogram and photo look after increasing the contrast.

On the left is the original photo, on the right is the result after a slight increase in contrast. As you can see, the work of contrast stretches the histogram, adding dark and light areas.

Why do you need a histogram?

All modern cameras are equipped with sufficiently large and high-quality displays. Why do we need a histogram then?

Displays have their own level of brightness, the perception of which also depends on the ambient light. If you look at the display at night, the picture will seem very bright, and during the day, on the contrary, it will be very faded. Due to the fact that the histogram shows the image in the form of a graph, it is independent of any viewing conditions.

The quality of displays in cameras is really high, but not enough to show the difference between almost white and absolutely white, as well as the difference between almost black and absolutely black.

Look at the following photo:

http://www.flickr.com/photos/bigfrank/368734607/

This is just the perfect photo for our situation. Of course it was processed in Photoshop, but it does not matter.

As you can see in the photo there are no overexposures or dark areas. The histogram shows us the same. There are not high bars along the edges, which indicate overexposure from lighting lamps and dark areas on the showcase. Otherwise, as you can see, the histogram shows that most of the information is in the midtones.

One glance at the histogram is enough to make sure that the exposure is correct and go on shooting.

As you already understood, each image has its own histogram, so there is no right or wrong histogram.

The histogram should be considered as a tool for quickly analyzing a photo during shooting (or during processing).

When to Use a Histogram

Night shooting
In the absence of external light sources, it is especially difficult to determine the brightness and contrast of a photo.

Studio photography
If you're shooting in a studio and don't have a light meter to measure the power of your fixtures, you have to work at random, adjusting your camera based on the result on the display. The histogram will more accurately show the situation in the picture.

Object shooting
Items are usually photographed against a white background. The photo can only show areas of overexposure. And the histogram will help you understand how white is really white.

Outcome

As you can see, the histogram is a very powerful and handy tool for a photographer. This is an absolute must for creating technically high-quality images. And in our next articles, we will continue to talk about interesting and effective tools for working with photos.

Graphs and diagrams

bar chart

What is a histogram?

A histogram, also known as a frequency distribution, is a visual representation of the distribution of data (for example, the height of 36 employees in inches). Information on a histogram is displayed using a series of rectangles or bars of equal width. The height of these bars indicates the amount of data in each class.

The frequency of events is indicated on the vertical axis, and the data group, or classes, are indicated on the horizontal axis. To evaluate a histogram, we need to know the central trend as well as the scatter of the data.

Measuring Central Tendency

• Mean (average value) - the sum of all measured or calculated data divided by the total amount of data; for example, add up all the data, get 2482, divide by 36 and get 68.9 inches.
• The value that appears most frequently in the raw data. In our example, this is 70 inches. If the data is presented as a group frequency, then we are talking about a modal class. The modal class is the interval with the highest frequency. In this example, the modal class is 68.5 - 71.5.
• Median - the middle of all measured or calculated data (if the number of data is even, then the median will be fractional); for example, in our example with 36 measurements, the median value is the average of those measurements that are in the middle (69+70=139, divided by 2, we get 69.5 inches).

Scatter measurement

• The range is the maximum value minus the minimum value.
• Standard Deviation (SD) is a measurement that shows how widely a set of data is scattered from the middle. All data is included in the standard deviation. It is much less susceptible to the addition of other data than the range, and therefore, it is a more reliable way to measure deviation.

Height of employees for histogram

Why is a histogram useful?

It is not always easy to look at measured data and identify patterns or analyze what the data tells us. A histogram can provide information about the degree of heterogeneity in the data and indicate the pattern of the distribution. By drawing a curved line across the tops of the histogram bars, we can get the big picture.

Scattering data can result in a wide variety of histograms, depending on the process or object you have collected data on. The following are some typical types of histograms.

Types of histograms

• Symmetrical (example A)
  Most values ​​are on either side of the center of the distribution (central trend) with deviation balanced on either side of the center.
• With slope (example B)
  Most of the values ​​are to the left of the central trend. This type of data distribution can happen if there is a natural obstruction, or in cases where the data is sorted (products that do not meet a certain standard are removed from the data set).
• Asymmetric (example B)
  On such a chart, there is a long "tail" on one side of the central trend. There are more deviations on one side than on the other, indicating that some variable values ​​have shifted during the process.
• Bimodal (example D)
  There are two vertices in the two modal type. This usually happens when two different datasets are mixed (the category of short people is mixed with the category of very tall people). In effect, we have two histograms merged together.

How to build a histogram?

To build a histogram, draw the horizontal and vertical axes. The horizontal axis (X) displays intervals; the vertical axis (Y) displays frequencies. Draw a bar representing the frequency of the data in each class. The strips should touch each other.

When to use a histogram?

The histogram can be used in the "Current Situation" step in the UC Outline chapter when we want to get an accurate picture of the scatter or spread of the data.

- This is a diagram of the tonal distribution of pixels in the image.

From left to right (horizontally) the brightness is indicated, and from bottom to top (vertically) the amount of area of ​​the photo of one or another key. It is often said that the vertical columns simply show the ratio of the number of pixels of a particular key. That is, the diagram shows how many light or dark shades prevail in the picture, how many green or red or other shades of colors the picture has more. Histograms are different. In photography, mainly three types are used:

1. General histogram (which is in the figure below).
2. A histogram for each of the three primary colors, such a histogram is often called RGB - red, green, blue - red, green, blue (as in other examples)
3. Hybrid histogram for general and primary colors (often, just overlay RGB histogram on top of histogram).

How to use the histogram

The histogram shows how many dark or light areas are in the picture, what is the overall balance of the picture.

A photo with a huge dark area. The histogram is “shifted” to the left.

The histogram is often divided into 3-4 parts. The leftmost part of the histogram is called "shadows" or dark tones, as this area shows how strong the dark areas of the image are. The far right part with "lights" or light tones, so this part shows how many bright areas are on the histogram. The middle - "penumbra" or medium tones. The rightmost part is sometimes called the blowout area, if there is a spike in the histogram in the far right corner, then most likely the photo is overexposed.

Why is a histogram useful?

1. With its help, it is easy to control underexposure (underexposed image) and overexposure (overexposed image). When overexposed, the peak (top in the diagram) will be visible on the right side of the histogram, and when underexposed, the peak will be observed on the left side of the histogram.
2. Fine-tune the exposure
3. Control color channels in a photo. The histogram can be used to determine the color saturation of an image.
4. Control the contrast. From the histogram, you can easily guess how much contrast the picture is.

What should be the histogram?

There is no single answer to this question. Ideally, the histogram should look like bell shape(when I studied at the institute, this form was called a Gaussian). In theory, this form is the most correct - after all, there will be few very bright and very dark objects in the image, and midtones in the photo will prevail. But as practice shows, everything depends very much on the type and idea of ​​​​the photograph itself. A histogram is a purely mathematical description of photography (art), and as you know, it is very difficult to describe beautiful things mathematically, especially with the help of such a simple method as a histogram. Therefore, there is no need to bring the image to a template view according to the histogram. The histogram should be used simply as an additional tool when creating a photo.

Photo histogram. The tone is shifted to the area of ​​light tones. The contrast is not high.

When do I use a histogram?

Personally, I use the histogram in only two cases - when you need to check the exposure of a picture in bright light, when the picture itself is almost invisible on the camera display. It can be the conditions of a summer beach or bright sun in the mountains. Under such conditions, it is simply not visible what is in the picture, therefore, I look at the histogram to roughly estimate the deviations. And, secondly, I use the histogram when editing photos, it is very convenient to determine the key in which the photo was taken by the histogram, and sometimes adjust the photo by adjusting part of the histogram curve. For example, sometimes I just take the “highlights” in the histogram and move them to the left with the slider - I move in the shadows, the photo is obtained without overexposure. Such a histogram, as in the examples in this article, gives ViewNX 2.

conclusions

The histogram is a useful tool for photography. Whether or not to use a histogram is up to you, you can do fine without it, or still understand its properties and use it when processing a photo or adjusting it accurately.

Thank you for your attention. Arkady Shapoval.

Paying or not paying attention to what the bar graph shows is your personal choice. But every photographer should at least know that such a tool exists and how it can be used. From this article you will learn "read" the histogram and recognize the tone of your photo from the histogram.

What is a photo histogram?

A histogram is a graph that shows the distribution of tones in a photo. I draw your attention to the fact that we will talk about the histogram, which contains information about the tones (not colors) in the photo. If we are dealing with an image in RGB format, then in such a histogram all channels will be presented at once.

There are also histograms separately by channels, which show the distribution of the red, green and blue channels (colors) separately in the photo, but I personally don’t use them at all.

Where can I find the histogram of an image?

You can open the histogram of a photo directly in your camera or when processing it in the Histogram information window in Lightroom and Photoshop. In Photoshop, the histogram is also presented in the windows for working with Levels (Levels) and Curves (Curves).

In a camera, the histogram is usually called up by pressing the Info button 2-3 times in a row in the preview mode. At the same time, the view of the preview representation changes - instead of a photo on the full screen, additional data about the file parameters and the corresponding histograms appear.

How to read the histogram of a photo?

The histogram shows how many shadows, midtones, and highlights are in your photo. The horizontal scale controls the tonality of the pixels, from the deepest shadows on the left, to the midtones in the middle, and to the brightest areas of the image on the right.

It is important to understand that the leftmost point is black point(completely deaf, underexposed areas without details), and the rightmost point - white point(the most burnt overexposed pixels, information about which is completely lost).

The vertical scale shows the number of pixels of each key in the photo. The higher the "peak" of the histogram, the more corresponding tones in the image. For example, in the photo histogram shown in the examples above, very high peaks occur on the left side of the histogram, which indicates that dark areas (in this case, a dark background) occupy most of the photo.

How to use a histogram?

Most often, the histogram is used to orientate, how correctly exposed. I especially recommend relying on the histogram readings for novice photographers, who still find it difficult to determine “by eye” whether there is enough light in the photo.

The basic rule in this case is avoid histogram peaks at extreme points, which talk about underexposure or overexposure in the photo.

Underlight. If the histogram is heavily shifted to the left and there are high peaks at the far left, this means that the photo has a lot of underexposed areas, i.e. there is a loss of detail in the shadows.

Peresvet. If the histogram is heavily skewed to the right, with high peaks at the extreme right point, then the exposure was too high, i.e. some parts of the image went into overexposure (loss of details in the highlights).

Both situations are two extremes that should be avoided when selecting exposure settings.

Correct exposure. In most cases, a histogram in which the peaks are located in the middle of the graph indicates a correctly exposed exposure. But this does not mean that all photographs need to be brought to some standard medium gray histogram. It doesn't happen and shouldn't happen.

It is important to understand that each photo has its own set of lights and shadows, and depending on the shooting plot and the author’s artistic idea, light tones or, conversely, shadows may prevail. Accordingly, the histogram of such a photo will be shifted in one direction. But this does not mean that the exposure was set incorrectly. Let's look at a few examples.

An “ideal” histogram only indicates the presence of medium-gray tones in an image. Here's what the above photo would look like when adjusted to fit the "ideal" histogram.

As we can see, the main distribution of the histogram peaks falls in the middle (midtones). At the same time, the photo looks flat, low-contrast, it clearly lacks saturation in the shadows and highlights. But we got maximum detail in both highlights and shadows. But is it really that important from an artistic point of view?

If you are initially filming a plot in which there are a lot of dark tones(dark background, dark clothing, etc.), the histogram will naturally shift to the left. Wherein gaps in the shadows are allowed, if these gaps fall on plot-insignificant areas of the photo (background, small areas in the shadows on clothes or environmental objects).

Reverse situation - when we shoot very light story(against a white background, against the light, a model with fair skin, in light clothes, etc.), the histogram will be shifted to the right. At the same time, d overexposures (completely white pixels) are omitted in plot-less important parts of the photo(background, details in the background, etc.).

Applied to portrait photography plot-important details are, first of all, the skin (face, hands, figure of the model), hair, and to a lesser extent, the clothes of the model.

Therefore, the basic rule for checking exposure in portrait photography is no overexposure on the skin of the model. Small highlights in highlights on clothes and accessories, and even more so against the background, are quite acceptable.

For example, in the photo below, the exposure is set to get the detail on the model's face and at the same time get a clear line of light and shadow on the face. At the same time, the shooting turned out to be almost silhouette, against the light, against the background of a large window.

Why is overexposure more to be feared than dips in shadows?

In digital photography (as opposed to film photography), the biggest problem is overexposure, because when too much light hits the area of ​​the photo is completely white, which means complete lack of information about the image. Such overexposed areas cannot be restored - even the RAW format will not save, because an error was made during shooting and the necessary data for building the image was not obtained.

Information in underexposed shadows is still preserved, so details even in the deepest shadows can, in principle, be pulled out in Lightroom (with the inevitable appearance of strong noise). We are not talking about maintaining image quality now.

For clarity, I will give an example. Photo of a high-contrast scene with a large spread in illumination between the lightest and darkest areas. Some average exposure value was chosen (neither yours nor ours). As a result, the bright sky outside the window went into overexposure (overexposures are marked in red), and the deep shadows inside the room fell into blackness (dips in the shadows are marked in blue).

When trying to bring back detail in the shadows by lowering the exposure to the limit, we are essentially filling with gray in those areas where there were overexposures. No details (clouds, tree contours, tonal transitions, etc.) could be returned.

If we try to bring back the details in the shadows, then when the exposure is increased to the limit, we can quite clearly see the texture of the wood on the legs of the chairs.

Conclusion

On the one hand, it is much easier to “get” the details of the image from the shadows, but noise inevitably creeps in; detail cannot be recovered from overexposure, but a slightly overexposed (up to +1 exposure stop) photograph can be brought to a decent appearance without the risk of noise.

As I personally do (this does not mean that this is the only correct option).

1. When shooting, I avoid overexposure in plot-important areas.

2. In critical situations, I prefer to slightly overexpose the frame to avoid strong noise when trying to pull out underexposed shadows. Then, during processing, I dim the lights, returning them to the “normal”

You may also be interested

When the digital age came to photography, it brought with it many benefits for photographers: taking a huge amount of photos without the price tag of film. We can see the shot taken immediately after shooting, we can change the ISO after each shot, in film photography it was necessary to change the film. But one of the most important advantages of digital photography is something that intimidates many novice photographers at first, and that bar chart.

But there's no reason to avoid it - the histogram is actually pretty easy to use once you understand how it works. bar chart is simply a graphical representation of the tonal range of your photo to help you evaluate exposure.

In the era of film photography, we had to wait until we developed the film to know for sure if we got a good photo or not. Now, using a bar chart, this information is at your fingertips.

How to read a histogram?

It's easy: The horizontal axis of the histogram graph displays the brightness of the tones in the photo. The left part is responsible for the darkest shades, the right part is responsible for the lightest shades, and the central part is responsible for the shades of medium brightness or as they are otherwise called semitones. The vertical axis shows how many pixels of this brightness are in the photo, the higher the peak on the graph, the more pixels

The most important thing to know about the histogram is that if the peak touches the right edge of the graph, then we have a photo problem. This is most of your image overexposed or even completely white, with no detail in the highlights. And the biggest problem is that the area that is overexposed contains no data at all, so you won't be able to do anything even in post-processing and even if you shot in RAW format. This only applies if the peak touches the edge of the graph. If it's a peak just before the edge, it's ok.

If the peak touches the left edge, it means that part of your image is completely black. You can use Exposure Compensation as a plus to correct your next shot. But if you are currently busy shooting at night, for example, the starry sky, then this is a completely “healthy” histogram for such a case.

There is no such thing as a perfect histogram. It's just a graphical representation of the tonal range in your image. It is up to you, as an artist, to decide what to do with this information. The presence of a large number of dark or light areas (provided that there are no overexposures and underexposures) is not necessarily a bad thing.

Let's look at some examples of what histograms would look like for different types of photos.

Histogram Examples

Scene filmed in high key

When you shoot in high key, the picture will have a lot of highlights and few mids and darks. When you want to photograph a scene in high key, your histogram should be shifted to the right - but not to peak on the right edge. If you wanted to capture a high key image, but your histogram shows a lot of shading in the middle of the graph, your highlights in the image will probably look more gray than you would like.

Pelicans in the Salton Sea, California

Stage in high key

The histogram for the image above shows a preponderance of highlights.

Stage in low key

The low key scene is the dark scene you get when taking photos at night. In this case, your histogram plot will be shifted to the left. Also, you may have a peak at the left edge, which indicates the presence of the darkest areas.

Such a scene will have the graph shifted to the left side.

The histogram for the photo above shows a dark scene.

high contrast scene

A high contrast scene is one with a lot of very dark and very bright tones, and maybe not as many midtones. In this case, your histogram will have rises on the left and right, and in the middle there will be either a dip or a flat chart.

High contrast scene. Extreme highlights and extreme darks and very few midtones.

The histogram of the high contrast scene is above.

low contrast scene

A low-contrast scene (tonally) has mid-tones, and quite a few highlights. The histogram of such an image will be in the shape of a bell. Please note that in tonal terms this is a low-contrast scene, and in color it is high-contrast.

Again, it is up to you as the artist to decide what to do with this information, whether to use it or not. It's just another tool in your arsenal to help you turn your artistic vision into great shots.

If you're not happy with the histogram of an image, use exposure compensation. With it, you can adjust the exposure by making the image darker or lighter. Or you can influence the lighting of the scene in other ways, using a flash, a reflector, or a diffuser. The choice is yours.

Understanding Color Histogram

You probably noticed in the examples above that the histogram not only shows brightness in grayscale, but also shows colors. Yes, you can over-exposure or under-exposure the color! It happens that there is some color that comes out very bright in the photo, and sometimes this color can be so saturated that you lose detail in it. This usually happens with red flowers, for example.

How to deal with it? The easiest way is to slightly desaturate this particular color in post-processing to bring back some of the detail in the flower petals. The histogram above shows an increase in red tones in the highlight zone.

When to Use a Histogram

While shooting, you can use the histogram in conjunction with Live View (when using a DSLR) to see it before you take the shot (or just turn on the histogram on the LCD if you have a mirrorless camera). You can also view the histogram after taking the photo. In any case, it's important that you use the histogram to make sure your exposure is correct while you're shooting in the fields. Thus, you will have the opportunity to retake the frame while you are at the desired location.

Do not rely solely on a visual inspection of the captured photo on the camera's LCD screen to assess the correct exposure, turn on the histogram. This is because the brightness of your LCD has nothing to do with the brightness of your photo.

The histogram is also available to you when post-processing photos in any graphics editor. Use it to see what settings need to be adjusted to avoid over-bright or over-dark areas in the image when processed.

I hope this gives you a better idea of ​​how to use this handy tool. If you have questions about the histogram, write them in the comments.