Why do people report that their eyes turn red when taking pictures?

The word "red eye" is actually aimed at people. When the flash illuminates the human eye, the pupil will enlarge to let more light pass through, and the blood vessels in the retina will turn red in the photo. Because the degree of red-eye phenomenon is determined by the depth of pigment in the subject, if the subject's eyes are darker, the red-eye phenomenon will not be particularly obvious. The phenomenon of human red eye is usually that when shooting in a dark environment, the pupil will expand to let more light pass through, so the blood vessels in the retina in the photo will be dyed red, but for animals, this phenomenon will occur even when shooting in sufficient light. ※ ■ How to eliminate red eye ※ Many cameras now say that red eye can be completely eliminated, and many digital cameras have red eye elimination modes in their flashlights. Can this annoying phenomenon really be avoided? Unfortunately, in fact, no camera can do this now. What they can do is to mitigate the impact of this phenomenon to some extent. Of course, some cameras are doing well, but the phenomenon of red eye does still exist. Red-eye phenomenon in animals is different. According to experts, pinkeye is very common in domestic animals. Pets' eyes usually have a reflective layer at the bottom of the retina, which can enhance their visual ability at night. Obviously, these reflective layers are different from the animal's own coat color, so the phenomenon will be different under the stimulation of the flash. For example, the black dog has a green radiation layer, so it is not a red eye phenomenon but a green eye phenomenon. Some animals, such as some dogs and rabbits, have no radiation layer of the eye membrane, so they will have the same red eye phenomenon as humans under the flash. ※. The phenomenon of human red eye is usually that when shooting in a dark environment, the pupil will expand to let more light pass through, so the blood vessels in the retina in the photo will be dyed red, but for animals, this phenomenon will occur even when shooting in sufficient light. There are many ways to realize the red-eye elimination system, but all of them are based on the same idea: reducing the magnification of the pupil, reducing the light shining on the retina, thus reducing the red-eye phenomenon. ※. There are two common ways to eliminate red eye. One method is to emit bright light in the same direction as the lens. Another method is to start the flash before exposure, or shorten the flash duration. In fact, red eye can not be completely eliminated by the above two technologies, and there are other factors that have an important relationship to eliminate the phenomenon of weakened red eye, which are beyond the camera itself. Luck is one of the factors. Why do you say that? If the subject is facing the camera, you will be very surprised at the result. There is no red eye phenomenon at all, and you don't even need to do red eye surgery. ◇ The "green-eyed" black dog just seen in the picture above is fine now, and there is no red eye in the picture. This is because the dog's eyes are facing the camera when shooting, which you can understand in practice. If the red-eye elimination function is turned on, but the glasses of the subject are staring at other places at the moment of shooting, then the red-eye elimination function is completely invalid. From the photo on the left, we can see that when the flash is turned on, the subject looks up. Although the red-eye elimination function is turned on, the result is still disappointing. The red-eye elimination system has no effect on the pupil, and this is the result. ◎ Tips ◎ There are some things we should know when taking photos that need flash. Whether the red-eye elimination function is turned on or not, the following techniques can help us effectively reduce the red-eye phenomenon. ◎ Put yourself in a position with a light source. When you shoot, the pupil of the subject will not be enlarged by strong light because of the illumination of ambient light. ◎ It is best not to shoot with a flash in a particularly dark place. After turning on the red-eye elimination system, try to ensure that the subject is aimed at the lens; ◎ Try to shoot in a well-lit place, so that the pupil will remain in a natural state; ◎ Use advanced flash with adjustable angle. When shooting, the flash should not be parallel to the direction of the lens, but move upward at an angle of 30 degrees with the lens, so that when flashing, an ambient light source is actually generated, which can effectively prevent the pupil from being stimulated and enlarged. It is a very difficult place to create a suitable light source or determine under what circumstances there is the best shooting light. Of course, both professionals and beginners are in the difference between these experiences and skills, and experience is constantly accumulating. ■ The ultimate solution ※ What should I do if I have red eyes after taking photos? Haha, don't worry, we will use the ultimate solution now, and adjust the saturation with software to eliminate red eye. This is our Photoshop solution. ◆ 1. Make sure not to touch the surrounding area. Needless to say, the selection method in PS. ◆2. Use the corresponding function (menu command) to reduce the saturation of the selected area, thus eliminating red eye. The following is the absolute skill in this operation: if the subject is black or brown eyes, adjust the saturation of the three main colors (red, green and blue) to a value close to 0, so that the red eye can be eliminated; If the subject has blue or green eyes, red eye can be eliminated by adjusting the red saturation of the three main colors to 0. ◆3. Finally, choose the area around the pupil of the eyeball to add black, so it looks natural. It refers to the phenomenon that the photographer's eyes appear red spots because of the reflection of the blood vessels in the fundus of the subject when shooting a portrait with a flash.