Red-eye elimination can be said to be a flash mode of digital camera flash.
After selecting this flash mode, the camera flash will pre-flash with a smaller brightness for a few times before starting to actually flash.
The reason is: the pupil of the human eye is larger when the light is dark. After a sudden high-intensity flash, the pupil has no time to shrink, and the red blood in the pupil and the blood vessels behind it leaves a blurring effect, causing The person in the photo has red eyes.
In the red-eye flash mode, the flash first uses a smaller brightness to pre-flash. The human eye's conditioned reflex causes the pupil to naturally shrink, and the color of the blood in the eye cannot be photographed during the official flash.