What does the straight side think?

In the histogram of a picture, the horizontal axis represents the brightness in the image, from left to right, from all black to all white; The vertical axis represents the relative number of pixels in the image within this brightness range. In this two-dimensional coordinate system, we can have an accurate understanding of the brightness of a picture. In Photoshop, click "image → adjustment → color scale (shortcut key: Ctrl+L)" to open the color scale adjustment box, and adjust the histogram of the image, thus controlling the light and dark changes of the image.

Figure 1 histogram legend

Characteristics of histogram

The histogram function in DC is the same as that in Photoshop. When the black color block in the histogram is to the left, it means that the overall tone of this photo is dark, which can also be understood as an underexposed photo. When the black color blocks are concentrated on the right side, it means that the overall tone of the photo is bright, which can be understood as overexposure unless it is necessary for special composition. Let's use a few photos to intuitively understand the image characteristics reflected by the histogram.

Figure 2 Precise exposure

Fig. 2 is a normal exposure photograph of a building and its corresponding histogram. We can see that in the left position of the histogram, the peaks are relatively high and dense, because there are many dark areas behind the building, and the position on the left side of the histogram reflects the distribution of dark areas. At the right position of the center of the histogram, we can see a higher peak, because the brightness corresponding to the large yellow area in the image is here. On the far right side of the histogram, we can see a small and prominent peak, which corresponds to the strong reflection of the cylinder on the building in the image. Because the brightness is too large, it is beyond the range that the histogram can express, so a peak is formed on the far right.

Judging from the content expressed by the histogram, the brightness of this picture is basically within its range, and there is not much overflow. More importantly, the brightness of every object in this picture accords with our general understanding, so we can think that the exposure of this picture is more accurate.

Figure 3 Overexposure Figure 4 Underexposure

In the same situation, if we increase or decrease the exposure when shooting, we will get the results as shown in Figure 3 and Figure 4 respectively.

In figs. 3 and 4, we can clearly see that. If the exposure increases, the dark part on the left side of the histogram is almost blank. If the exposure is reduced, the opposite result will appear in the histogram. In this way, if we see a histogram, we can have an accurate understanding of its brightness even if we don't look at the image.

It should be pointed out that it is not the image whose peak is centered and relatively uniform in the histogram that is suitable for exposure. The key to judge whether the exposure of an image is accurate depends on whether it accurately reflects the photographer's intention. For example, in the usual night scene pictures, the peaks of dark areas are mostly in the histogram.

Taking Figure 5 as an example, there is a large area of black in the histogram concentrated in the left area, which shows that there are many shadow parts in the image, which is also in line with people's general concept of night scene. There is also a relatively small peak at the right end of the histogram, which corresponds to the highlight caused by light in the image. Although the lines in this histogram are not evenly distributed in the center, it is also an example of correct exposure because of the special scenery. This situation is rare in daily life photos, but I believe it will be very helpful for everyone to understand the concept of histogram.

Figure 5 Night exposure

Actual combat histogram

After understanding the basic concepts and information of histogram, how to apply relevant knowledge to daily photo shooting? After all, DC's EVF viewfinder and LCD viewfinder are limited by their own display characteristics such as brightness, color saturation and sharpness, and there will always be some differences in image performance, which will directly affect our accurate judgment and choice of photo brightness (exposure). The appearance of histogram just supplements this deficiency.

Specifically, the application of histogram in DC can be divided into two aspects: on the one hand, the exposure of the image can be checked after shooting; On the other hand, before the photographer presses the shutter, it provides an accurate reference for the light and dark distribution of the picture, and the photographer can adjust the exposure parameters according to the actual needs to ensure the exposure accuracy of the photo.

Then, let's explain in detail how to use the histogram function more reasonably in shooting to get accurate exposure photos.

How to use 1. histogram?

At present, most mainstream cameras have histogram function. Take Sony F828 digital camera as an example. Before shooting, the camera can display the corresponding histogram information on the LCD screen of the camera according to the different viewing angles (see Figure 6). If the current histogram shows too much dark information, it means that the image is underexposed, and the photographer can appropriately increase the exposure to make the curve in the histogram shift to the right as a whole, so as to obtain the correct exposure. According to the histogram that changes at any time, it can be determined whether the appropriate exposure parameters have been adjusted. or vice versa, Dallas to the auditorium

Fig. 6 is a view showing a histogram.

So we can know the exposure of the picture according to the built-in histogram function of the camera. Then, how can we see the histogram with uniform color level distribution by further adjustment?

2. Exposure adjustment

In order to get a photographic work with suitable exposure, we can change the exposure parameters in various ways until the color scale distribution of the image displayed by histogram reaches our shooting purpose. The following three examples will show you how to use different shooting techniques to achieve accurate exposure (note: in order to show the histogram more clearly, this example will be represented by histogram in Photoshop).

Method 1: Use the exposure compensation function to directly adjust the exposure.

Fig. 7 Underexposure

Figure 7 shows the lively night market lights in Causeway Bay, Hong Kong. The whole picture is dominated by various light box signs and neon lights. The two peaks of the histogram are concentrated on both sides and overflow, indicating that if the contrast between light and dark is too high, the details of the light and dark parts of the picture will be irreversibly lost. Analyzing the situation at that time, it is easy to see that many scenes are "hidden" in the dark area of the histogram and are not shown.

Figure 8 Moderate exposure

At this time, the exposure compensation (+EV) of 0.3 ~ 0.7 can be added, and the effect of Figure 8 can be obtained. As you can see, the dark field just now adds a lot of details, and the performance of the whole image is closer to the naked eye.

At this time, if the exposure compensation (+EV) of 0.3 ~ 0.7 is added, the effect shown in Figure 9 will be obtained: the image is much brighter, but the noise in the dark part is obviously increased, and the whole picture has no night scene atmosphere. Therefore, if it is exposed as shown in Figure 9, the details of the dark part can indeed be fully reflected, but if the bright part is overexposed, the imaging effect will be poor, which is the reason for too many reasons. Therefore, if we see the serious loss of bright details caused by overexposure as shown in Figure 9 on the histogram, we can correct it by subtracting the exposure compensation (-EV) of 0.3 ~ 0.7, and get the effect as shown in Figure 8.

Figure 9 exposure transition

Many cameras now offer shortcuts similar to the exposure compensation function. If not, you can also find the corresponding options in the camera menu.

Method 2: Flexible use of measurement methods.

The exposure of the camera is calculated by its built-in photometry program after determining the brightness and other data, combined with the exposure data in the camera. In general, the default metering scheme is central focus metering, which can get correct exposure parameters in most cases. However, there are exceptions. At this time, we can use the spot metering function of the camera to measure the area with neutral gray brightness (similar to the middle zone between light and dark), and get the appropriate exposure parameters that can meet most conditions. Similar metering methods include multipoint metering and so on. , according to the specific function of the camera, combined with experience to apply.

Method 3: Adjust the exposure parameters directly.

Experienced photographers can roughly estimate the amount of exposure that should be compensated according to the histogram data, and manually adjust the exposure parameters such as aperture and shutter. Not only can we get proper exposure, but also we can get more reasonable exposure parameters by considering the depth of field and exposure speed comprehensively according to the actual situation.

There are many ways to change the exposure, but no matter which method is adopted, the key is to understand the meaning of histogram, so as to ensure that you know your own shooting results before shooting, so as to shoot an image with reasonable color distribution.

3. The real meaning of using histogram

The real significance of determining exposure parameters by referring to histogram information is to directly see through the internal information of the image, so as to obtain the most suitable exposure parameters, which will not be affected by the difference between the display effect of EVF or LCD itself and the actual image exposure. Because the physical characteristics of the input and output devices related to the image are inconsistent, especially in the home environment, it is more difficult to get a unified color description in a strict sense, which is why we didn't get what we saw when shooting and what we browsed and printed after shooting, and the histogram abandoned the surface expression of the image and gave us a quantifiable standard for later output with real and reliable data. Therefore, if you want to be a small-scale photographer, it is essential to know the histogram.

Hope to adopt