Why is the LED on the back of my Apple phone on when I take a picture, but the picture is black?

Like the human eye, when the camera is illuminated by strong light, the corners of the backlight will darken.

Both mobile phones and cameras take photos by metering. When the contrast between the brightest and darkest parts of the scene is great, it is impossible to take care of both ends. At this time, the final image is either partially overexposed or partially underexposed, that is, some parts of the picture are too bright or too dark. This is actually an insurmountable difficulty, and a typical scene is like shooting against the light. Therefore, we often see that the pictures taken by backlight often have a dead black foreground. This is also the reason why photometry has become a difficulty in photography.

In order to solve this problem, the mobile phone represented by iPhone puts forward a solution, that is, click a certain position in the shooting interface, and the metering system focuses on what the user chooses at this point, that is, to ensure the brightness of the point selected by the user, and the metering system uses this point as a reference to adjust the brightness of the whole picture. For example, if you take a photo in a backlight environment and click on a dark foreground in the picture, the picture will not hesitate to overexpose the background to obtain a reasonable foreground brightness.

There are other photometry methods to solve the contradiction of excessive contrast by taking the average brightness of the picture or other means. Each method has its limitations.