What are exposure compensation, white balance and ISO sensitivity? (photographic terminology)

Exposure compensation is also an exposure control method, generally around 2-3EV. If the ambient light source is dark, you can increase the exposure value (such as+1EV, +2EV) to highlight the clarity of the picture.

White balance is a very important concept of camera.

The so-called white balance is the restoration of white objects by the camera. When we look at the world with naked eyes, we feel the same color under different light. For example, when the sun rises in the morning, we look at a white object and think it is white. And when we see a white object in the dim light at night, we think it is still white. This is because the human brain has adapted to the color reproduction of objects in different light during its growth after birth. But as a camera, it has no adaptability to human eyes. Under different lighting conditions, due to the imbalance of CCD output, the color of the camera is distorted: the image is either blue or red, as shown in the figure.

The color of the image in the middle of the picture below returns to normal, while the image on the left is obviously blue and the image on the right is red, so the images on the left and right are all images with abnormal white balance.

In order to understand white balance, we must understand another important concept: color temperature. The so-called color temperature, in short, is to use Kelvin temperature to quantitatively represent color. When an object is heated to a certain temperature by an electric lamp or the sun, it will emit certain light, which contains not only brightness components, but also color components. The higher the color temperature, the more blue components and the bluer the image. Conversely, the lower the color temperature, the more red components, and the image will be reddish. Therefore, if the light that illuminates an object changes, its reflected color will also change, and this change will be reflected in the camera, which will produce different color reduction phenomena under different light. The following table shows the color temperature under some light.

Color temperature of light source (k)

Candle 2000

Tungsten lamp 2500-3200

Carbon rod lamp 4000-5500

Fluorescent lamp 4500-6500

Daylight (average) 5400

Cloudy sunshine 6500-7000

Cloudy sunshine 12000- 18000

As can be seen from the above table, the color temperature under different light is very different, which leads to different color reproduction of the camera under different light. In order to solve this problem, all current cameras have the function of white balance correction to compensate different color temperatures, so as to truly restore the color of the subject.

Now all cameras have the functions of automatic white balance and manual white balance. Automatic white balance enables the camera to automatically correct the white balance within a certain color temperature range, which is between 2500 K and 7000 K. Beyond this range, the camera will not be able to automatically correct the color of the shooting picture, so the manual white balance function should be used to correct the white balance. Please refer to the related articles on using skills for specific operations.

References:

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Many digital photography enthusiasts have had this experience: when they encounter a rare beauty, they press the shutter cheerfully and turn on the computer at home, only to find that some of them are scrap films; Or because of insufficient exposure, it is impossible to show nuances; Or the hand-held exposure time is too long to shake, or it may be because the high ISO is selected, resulting in serious picture noise ... These problems are difficult to detect on the small LCD behind the digital camera, but they are undoubtedly exposed on the computer screen. It is really difficult to measure the time, energy and mood wasted by photographers during this period with money.

The reason is that most digital cameras (including early film cameras) are designed according to the most common lighting environment. In such a well-lit environment, you can often choose the most suitable aperture and shutter to shoot, so as to get better shooting results. However, as a master photographer said, photography is the art of light and shadow. In this case, photography does not have to be carried out in a certain lighting environment. For example, if you want to shoot a moving object in poor light, you can't extend the shutter time, otherwise the shot object will become blurred. Therefore, the most fundamental way for your camera to cope with various shooting environments is to provide a wide range of sensitivity options.

In the film age, the way to change the sensitivity is to choose films with different ISO values. For example, ISO 100 corresponds to the basic shooting environment, so ISO200 means that the sensitivity to light is doubled and it can cope with dark environment, while ISO400 doubles the sensitivity, and so on. The photosensitive element of digital camera is CCD fixed on the fuselage, and we can adapt to different shooting occasions by adjusting the sensitivity of CCD. Originally, it is a very obvious advantage of digital camera to change ISO value at any time without completing a roll of film.

However, most digital photography enthusiasts do not enjoy this benefit: although most digital cameras offer options such as ISO200 and ISO400, they will find that these options are actually flashy in actual shooting. On the one hand, the image quality of these cameras under ISO200 and ISO400 can't be compared with ISO 100 at all, and the appearance of huge noise makes the picture horrible. On the other hand, in the case of dim external light, these cameras tend to focus slowly, and the shutter lag is serious (sometimes as long as half a second), so they can't capture fleeting moments, and the fun of photography has plummeted.

In the past, those professional players who could perform normally under high ISO conditions were all expensive digital SLR cameras. Because the CCD(CMOS) size of these cameras is relatively large, the area of each pixel is much larger than that of ordinary digital cameras, which can effectively suppress the noise. However, large-area photosensitive elements are also the fundamental reason for the high price of these cameras, which is naturally not a way that home digital cameras can imitate. In 2005, many digital camera manufacturers introduced some digital cameras with high ISO options. However, due to the simple improvement of sensitivity, the noise situation is quite serious at high ISO, so it cannot be used. Or we have to greatly reduce the resolution of digital camera under the condition of high ISO setting, as a last resort to ensure the cleanliness of the picture. However, in this era, do you still want your photos to be only 3 million pixels?

So, what direct benefits will a digital camera with "high ISO" capability bring? First of all, "high sensitivity" technology can solve the problem of night shooting. In the past, night scenes were either exposed for a long time or shot with a flash. If it is a long exposure mode, a tripod must be used to ensure the stability of the camera itself, but a heavy tripod is a great burden for travel.

The characteristics of the flash also determine that it can only solve the brightness of the foreground, but not the background, resulting in a night scene with only the foreground and no background. "High sensitivity" technology fundamentally solves this problem. Because it is more sensitive to light, in the "high sensitivity" state, it only needs normal shutter speed, that is, it does not need a tripod, and there will be no bright foreground and dark background.

Secondly, the "high-sensitivity" technology allows us to use a higher shutter speed to achieve the purpose of snapshot under the same shooting conditions. We found that children and pets are one of the most important shooting contents at present, and their similarity lies in that it is difficult for you to pose in a stable position for shooting. According to the experience of most users, if the shutter speed is lower than115 seconds, the discharged photos tend to be blurred. With "high sensitivity" technology, we can double the shutter speed. For example, in ISO400 state, it can be four times higher than ISO 100, and every vivid expression can be captured at the speed of 1/60 seconds. And if it is under ISO 1600, the speed can be as fast as 1/250 seconds, even a fast-running pet can't escape your lens.

Finally, the "high sensitivity" technology also makes shooting easier, because the high shutter speed brought by "high sensitivity" not only solves the motion of the subject, but also eliminates the slight jitter of the photographer's hand. In fact, in many cases, the slight jitter of the photographer's hand is an important factor affecting the shooting quality, especially for the thin and compact digital card machine, the action of pressing the shutter may bring camera jitter, and the only solution is to increase the shutter speed. "High sensitivity" technology can improve the shutter speed without affecting the shooting, and achieve the purpose of "anti-shake".