Knowledge about the principles of digital cameras

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(1) When a digital camera is used to photograph a scene, the light reflected by the scene passes through the digital camera'sLensTransmittedCCD.

(2) When CCD is exposed,DiodeWhen stimulated by light, a charge is released to generate an electrical signal of the photosensitive element.

(3) The CCD control chip uses the control signal line in the photosensitive element to control the current produced by the light-emitting diode, Which is output by the current transmission circuit. The CCD will collect the electric signals produced by one imaging, unified outputAmplifier. (4) signals amplified and filtered are transmittedAdThe ADC converts an electrical signal (analog signal) to a digital signal. The size of the value and the intensity of the electrical signal are directly proportional to the voltage. These values are actually the data of the image.

(5) At this time, the image data cannot be directly generated or outputDSP (Digital Signal Processor)In the DSP, color correction and white balance processing will be performed on the image data, and the image format and resolution supported by the digital camera will be encoded, then it is stored as an image file.

(6) After completing the above steps, the image file will be saved to the memory and we can enjoy it.

Relationship between focal length and Angle of View

Redeye:

The so-called red eye refers to the phenomenon in which the pupil of the human eye shows red spots when a digital camera takes a close-up of a person in flash mode. To avoid the occurrence of the red eye, you can turn on the digital camera's "Remove the red eye" mode, first let the flash once or several times, so that the human eye pupil is reduced and adapted, then the formal flash and shooting

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How to remove the red eye when taking a photo

"Red Eye" refers to the appearance of red spots in the pupil of the human eye in the photo when a portrait is taken with a flashlight.

In a relatively dark environment, the pupil of the human eye is enlarged. If the optical axis of the flashlight is close to that of the camera lens, strong flashlight light is reflected into the lens through the human fundus. the fundus has abundant capillary vessels. These vessels are red, so a Red Spot is formed. This problem occurs when you use a built-in flashlight that is close to the lens.

Redeye protection is a feature of flash. It pre-flashes before the official flash, narrowing down the pupil of the human eye, thus reducing the redeye phenomenon. The "Red Eye" phenomenon often occurs when taking portraits (especially close distances and dark environments. If you do not want the eyes of the person or animal to be shot to be "red-eyed", you can use the "remove red-eyed" mode of a digital camera to first flash the flashlight one or several times, after the human pupil adapts, the main flash and shooting will be carried out. When using the flashlight to assist shooting, note that the shooting distance should be within the effective coverage of the flashlight. The built-in flash coverage of low-and middle-end digital cameras is limited. For Photography enthusiasts, The Flash index is low (generally in the range of 1 ~ Within 9 meters), but basically meets the needs of normal shooting

From: http://wenku.baidu.com/view/4432baf8770bf78a6529541f.html

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From: http://hi.baidu.com/leiziluck/item/7a4cb003eb2fa8d21ef0467f

★How to eliminate the red eye★

Nowadays, many cameras indicate that they can completely eliminate the red-eye phenomenon. Many digital cameras use the red-eye elimination mode in their flash. Can this annoying phenomenon be avoided? Unfortunately, no camera can do this now. What they can do is to reduce the effect of this phenomenon to some extent. Of course, some cameras do a good job, but the phenomenon still exists.
The term "Red Eye" is actually for people. When the flashlight shines on the human eye, the pupil will zoom in to let more light pass through, the blood vessels in the retina become reddish on the photos. If the recipient's glasses are of a darker color, the intensity of the appearance is determined by the depth of the color. Therefore, sometimes the appearance is not particularly obvious, for example, the human eye in the legend on the right.
The red eye produces different phenomena for animals. According to experts, red eyes are common in livestock. The eyes of pets usually have a reflex layer at the bottom of the retina, this can enhance their vision ability at night. Obviously, these eye mask reflective layers are different from the animal's own hair color, so they may be different under the flashlight stimulation.
　
Human redeyes are usually shot in a dark environment. Pupil enlargement allows more light to pass through, so the blood vessels in the retina will become reddish in the photo, for animals, this can happen even when there is plenty of light.

Redeye elimination series

◇ The red eye elimination system has a variety of implementation methods, but it is based on the same concept: reducing the magnification of the pupil, reducing the amount of light exposed to the retina, thus reducing the red eye phenomenon.

◇ There are two common ways to remove the red eye, one of which is to emit bright light in the same direction as the camera, another method is to enable the flashlight first and then expose it, or shorten the flashlight duration.

◇ In fact, none of the above two technologies can completely eliminate the red eye. There are also some other factors that are important to the elimination of the red eye phenomenon, which are beyond the camera itself.

◇ Lucky is one of the factors. Why do we say this? If the shooting object is exactly in the direction of the camera, the result will surprise you, and there is no red eye at all, you do not even need to perform the elimination operation with red eyes.

◇ The black dog that has seen the "Green Eye" phenomenon just now is normal, and there is no red eye in the picture. This is because when shooting, the dog's eyes are completely directed at the camera, you can understand it in practice. If you have enabled the redeye elimination function, but the glasses of the object you are shooting are staring at other places, the redeye elimination function will be completely ineffective. From the picture on the left, we can see that, when the flashlight was started, the shooting object looked above. Although the redeye elimination function was enabled, the results were disappointing. The redeye elimination system did not have any effect on the pupil, this is the result.

　

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Workflow of the DSP chip in the camera: