Cheats Two important laws in different contrasts

Medium-tone, according to the gray exposure-why the tone is not required to arbitrarily increase or decrease exposure volume?

In digital photography is more prevalent a saying: exposure better than owe. How does the dark part of the digital image show more levels? Exposure is less of a problem, so this approach is a safer way. The problem is that "better to owe not" photos have to be adjusted to achieve the best. Every picture has to be adjusted, the workload is too big, very troublesome.

In the 1.2 section of the detailed discussion of the advantages of digital, the correct shooting can make the photo latitude at least to reach 11 levels. There are such indicators, why do we have to "better than owe" to create trouble? The shooting habits of insurance and security prevent us from making full use of the advantages of digital cameras. I have in more than a year time in particular recommended "Ning long not Over", half of the "safe" shooting way, until one day I saw Canon company to provide a group of digital original film, photo-Ming Transparent, elegant color. Out of curiosity, I took a serious look at the metadata of the photos, proving that the photos had not been adjusted for the time being. I'm heavy, the same camera why can't we get a picture that doesn't need to be adjusted and one-step? Such a small matter has promoted my understanding of digital latitude and saturation. I soon mastered this one-step shooting technique. Of course, one-step is a prerequisite, that is, for the theme of the constant tone, too high or too low contrast difficult to achieve a step in place.

Medium-tone refers to the contrast between the usual, high light and dark light ratio between 1:64 and 1:128, that is, 6~7-level aperture, soft light, Pingshun and other conditions. The key is the light is relatively small, the overall illumination is not related to a large number of digital can be in this condition "correct exposure" and get no need to adjust the quality of the picture. The "correct exposure" here refers to the principle of the gray value metering in 18%, regardless of the point measurement, bias central metering or average metering, as long as the metering point in the screen in the gray mean, you can get the exposure parameters of the bold exposure, without fear of high light loss and random exposure, Take full advantage of the best latitude and recording capabilities of the camera without suspecting the camera.

How to identify this picture is the best? Many people are accustomed to looking at photos on the camera's LCD screen and the display, and then come to the conclusion. It can be said that the vast majority of people do not put the LCD screen brightness, on-site environment and display is not allowed to solve problems, so the conclusion is often inaccurate, it is recommended that the camera LCD screen brightness to the middle of the lower point, watch the time to avoid direct sunlight. In addition, if the human eye and the camera LCD into the right angle relationship, see the screen sometimes will be light, so the camera and eyes are about 105o of the angle to see the screen, shot out of the photo exposure is often more accurate. Please refer to the section "What is a qualified photograph" in 8.2.2. The photo's high light data is between about 245, black between 0~8, the photo exposure is the best state, can flush, print, print high-quality photos.

Figure 3-39

Figure 3-39 is a photo taken by a digital camera of Canon model. The metadata shows that it has not been adjusted.

Figure 3-40

We use data and histograms to interpret this picture (Figure 3-40). First look at the histogram, hierarchical distribution of continuous, smooth convergence, there is no suspended and fault and comb-shaped notch band. The peak display coincides with the picture's tone distribution, and the corresponding sampling data in the graph is very consistent with the display view. Elegant white clouds have a hierarchical transition, not dead white 255. The average value of the gray-area data is about 126, which is very close to the absolute equilibrium Grey 128. The highlight is black, R2 G5 B4 is perfect for black, not all for 0 of dead Black, which is a good illustration. Digital is completely possible to take a shot in place, not to undergo late adjustment.

Figure 3-41

Figure 3-41 is a picture taken at five Huahai on a dam. Inspired by the analysis of the sample, this kind of often contrasting scenes, using the central average metering, do not do exposure compensation, the correct metering after the exposure value directly shot, the photo color, contrast, density are very ideal, do not need to undergo any late adjustment.

Figure 3-42

Let's take this picture for color analysis (Figure 3-42). This picture does not have the big shadow, the contrast often, the light is smooth, can maximize the latitude of the digital camera. Using the same type of camera with the sample, this photo sets the medium saturation, the level of white clouds is very rich, Baiyun area of the highest brightness of R250 G250 B255, a large area of white clouds R246 G247 B252. The recent cloud level occupies most of the high light area, so the level of white clouds is quite rich. The distant mountain R88 G90 B117, correctly corresponding to the blue-green mountains formed by the air perspective. Dark black and layered hair, not all 0 of the dead black. The medium saturation setting makes the R data in black slightly higher than expected. The color is slightly more vivid than canon sample is caused by high saturation in the setting. I took a lot of digital photos, to tell the truth, not after the adjustment of the photo shoot one-step few. The reason, or because of the early stage of various settings and the specific situation of the scene there are differences, so the digital early shooting to achieve the best effect is indeed not a very easy thing to do.

Figure 3-43

Figure 3-44

After the experiment, I think the latitude of the digital camera is not less than 10, and most of the main level of contrast screen in the 7-level light ratio (as shown in Figure 3-43, do not exclude the screen has a very small picture of the very white and extremely black). These small area structures have no fundamental influence on the main body of the picture. The "brightness" in figure 3-44 is the average of the RGB of the grayscale, and the differential of the "light ratio" for each of the 1-level EV values. A digital camera can easily record a 7-level light ratio without having to adjust it later, according to the gray value metering and exposure. Note, however, that it is critical to have the photometric and exposure of the gray value and to determine whether the gray area will be used in the correct metering mode when metering.

Let's use this picture again to see what's going on over exposure. Although the digital camera has 10 levels of latitude, but when exposed, if you choose the light gray area, it may be wrong to the gray area as a grey area and caused the error of judgment, that is, in order to ensure that the brightness of the level of the record focus on the high light, at this time the dark part of the exposure, there is no layer on the original film, these films This approach can greatly expand the digital latitude, is a major advantage of digital. This kind of filming is common in negatives of "press the dark part to expose, according to the High light development", but also a classic exposure, but in the digital camera will cause high light exposure, the formation of dead white, the death of White can not be improved and adjusted in the later, so unless special circumstances, can not use this method of filming (Figure 3-45).

Figure 3-45

There is a phenomenon of digital camera quality, which can be divided into two categories: High picture and low picture, with noise size as the limit. The noise is so small that it is difficult to detect for high quality. This level is located between the latitude 7~8 files. High-quality parts of the image, whether from the definition, color, texture and all aspects have excellent performance. And obviously can see the low quality image of noise, take ISO100 as an example, dynamic range can reach 11 level. In the more than 4, the image quality will be slightly inferior to the high-quality, mainly in the presence of larger noise. The size of the noise and the camera's brand, some brand camera pictures of the stone's noise is very small, the level of the image has little effect, completely acceptable, and some brands of the picture is more noisy, readers can be based on their own comparative experience. Generally speaking, the price of high camera noise low, a penny a penny, in line with the value of law.

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• PS Image Processing