Understanding Camera Histograms While Shooting-1024programmer

Summary：

We have two previous articles on the impact of shutter speed, aperture and sensitivity on photo exposure：

【Notes】 Grasp the three elements of exposure （up ）：shutter, aperture, ISO

【Notes】Three elements of exposure （ Application of Aperture and Sensitivity

Through those two articles，We know how to achieve normal exposure by adjusting the shutter, aperture and sensitivity under overexposure or underexposure. So how do we judge whether a photo is properly exposed when shooting?? You can see it through the histogram. This article will talk about the use of the histogram in the early stage of shooting.

1. The concept of histogram

Histogram in digital photography 中 is a very useful tool，you can clearly see the brightness information on the photo through the histogram，and then judge whether the photo is underexposed or overexposed，that is to say， After a photo ， check the histogram in time， can effectively judge the exposure of the photo. We can see the photo histogram through the camera display screen, LR, ACR, PS, mobile phone APP and so on. The picture is an example of a histogram：

The picture below is the histogram we can see in the camera，We can directly view the histogram information when shooting ：

In the early stage of shooting，the information we can get by looking at the histogram is the brightness information of the photo，so we have to explain the brightness information first.

When we look at a photo or describe the brightness of a certain scene, we usually use descriptive words such as very bright, very bright, very dark, very dark, etc.，but for machines Such a description is basically a black question mark. How does the machine represent the brightness? ？ is to use numerical values ， in the numericalization ， the brightness is divided into 256 values from 0 to 255 ， the larger the value ， the brightness The brighter ， 0 means no light ， is the darkest pure black ， 255 means the strongest light ， is the brightest pure white ， and the value in the middle represents Grays of different shades. As shown below ：

Back to the histogram，We create a coordinate axis，The horizontal axis represents the brightness value of 0-255，The vertical axis represents the corresponding brightness The number of pixels，forms our histogram. As shown below ：

Second, the correspondence between histogram shape and photo brightness

Above we explained the concept of histogram&# xff0c; Next, let’s explain the correspondence between the histogram and the brightness of the photo.

We cut the histogram ， into several parts ， from left to right are black, shadow, middle tone, highlight, white ， as shown below &#xff1a ;

Corresponding to the photo is the black area, shadow area, normal brightness, highlight area, and white area. Generally speaking,，the details in the normal brightness area are the richest，and can be seen intuitively；while the shadow and highlight parts，have details，but may be seen by the naked eye It’s harder to see，We can get back the details of these areas by brightening the shadows or darkening the highlights；The black and white parts can bring more layers to the photo；while The far left of black is pure black，The far right of white is pure white，These two areas cannot be brightened or darkened，There is no way to retrieve the details， That is, these parts of the photo are missing details.

In order to better understand ， Use a few extreme pictures to show the performance of the photo brightness in the histogram （ All the histograms below are available in the mobile phone software snapseed See ）.

This is a pure black picture，In the histogram, all pixels are on the far left（It can be understood that the pure black is underexposed， Did not record any details， No matter how we increase the exposure and brighten the shadows in the later stage, we will not be able to retrieve the details，xff09;：

This is a pure white picture ， in the histogram, all pixels are on the far right （ It can be understood that the pure white area is too much The exposed & # xff0c; details are also lost & # xff0c; No matter how we lower the exposure and darken the highlights in the later stage, we will not be able to retrieve the details & # xff09;&# xff1a;

This is half of a picture Pure black and half pure white picture，high contrast between light and dark，in the histogram, half of the pixels are on the far left，half of the pixels are on the far right：

This is a picture with more shadows and dark areas of the picture，We call it a “low key” photo，in the histogram, it shows that most of the pixels are piled up on the left：

This is a picture with more highlights and bright areas of the picture，We call it a “high-key” photo，In the histogram, most of the pixels are piled up on the right&#xff1a ;

This is a high-contrast picture （ that is, the light and dark are relatively clear ， the mid-tone brightness is relatively small ， its extreme case It is half pure black and half pure white ），in the histogram, it shows that there are more pixels accumulated on the left and right sides，while the middle pixels are less（both sides are taller， Middle low ）：

This is a low contrast image ，photo will look gray，shown as stacked pixels in the middle of the histogram There are many，while the black and white areas on the left and right have almost no pixels：

At this point， we should be able to roughly know the histogram The corresponding relationship between the shape of the graph and the brightness of the photo. Look at another picture，Consolidate it：

Then let’s talk about the role of the histogram in the early stage of shooting.

Third, look at the histogram when shooting ， find the overexposure or underexposure in the photo

In our usual photoshoot&#xff0c ;Generally, there will be no extreme cases where the entire photo is pure black or pure white，More often, the histogram of the photo is distributed on the entire coordinate axis，a so-called normal exposure photo& #xff08;What needs to be noted here is that ， what we are talking about is a normal exposure histogram， does not mean that it is an iron law， nor does it mean that it is the most correct histogram&#xff0c ;There is no most correct histogram，Only the most suitable histogram！），The histogram is mainly piled up in the middle part，and slowly transitions to the sides（ It is normally distributed ）， and there are no tall columns on the far left and right （ that is, there is no histogram like the pure white or pure black photo above）&#xff0c ;As shown below ：

But generally the parameters we shoot are not set properly，It will lead to overexposure or underexposure of the photo，reflected on the histogram&#xff0c ; That is, there are tall pillars on the far left or right.

This is a severely underexposed photo ，shown on the histogram ，a lot of pixels piled up on the far left：

This It is a severely overexposed photo，shown on the histogram，a large number of pixels are piled up on the far right：

The above two examples are what we generally say There are dead white and dead black areas，that is, a considerable number of pixels are accumulated in pure black or pure white areas，These areas cannot be retrieved through post-processing，so we This should be avoided during normal shooting. If in actual shooting，the leftmost part of the histogram is seriously overflowed（underexposed）， then we may consider increasing exposure compensation, reducing the shutter speed, and opening a large aperture , increase the ISO, etc. to increase exposure ， and if you find that the far right of the histogram is seriously overflowing （overexposed）， then we have to consider reducing exposure compensation and increasing the shutter , Reduce the aperture, reduce the ISO and other ways to reduce the exposure.

Some people may think that ，our human eyes can usually judge whether a photo is overexposed or underexposed by looking at the photo，in actual shooting, we rarely look at the histogram. To be honest，During my shooting，I haven’t developed the habit of checking the histogram after taking photos，but in fact, due to the effect of the display screen, the ambient light is too glaring and other reasons ，We may not be able to accurately see the brightness information of the whole photo， Only through the histogram can we accurately grasp whether there is dead black in the dark part ， whether there is dead white in the bright part， in order to improve our shooting Success rate.

Of course，It is not to say that only the normal distribution histogram with high middle，low sides is correct，The histogram is only a guide，In the early stage It is limited to allow us to know the brightness information of the picture in a timely and accurate manner. Sometimes ， in order to express our theme， we have to deliberately overexpose or underexpose the photo （like the high-key and low-key photos above），The point is you Now I can use the histogram to understand the exposure of a photo， and learn how to adjust it.

�This happens. If in actual shooting，the leftmost part of the histogram is seriously overflowed（underexposed）， then we may consider increasing exposure compensation, reducing the shutter speed, and opening a large aperture , increase the ISO, etc. to increase exposure ， and if you find that the far right of the histogram is seriously overflowing （overexposed）， then we have to consider reducing exposure compensation and increasing the shutter , Reduce the aperture, reduce the ISO and other ways to reduce the exposure.