On the blur of photographic images. The red clothes in the picture are in sharp contrast with other colors in definition.

This is the background blur effect made by shallow depth of field.

Use a large aperture when shooting; If it is a zoom lens, try to use a long focal length; The subject should be as far away from the background as possible, that is, let the red clothes in the picture leave a little distance from other clothes; When shooting, the lens should be as close to the red clothes as possible without affecting the composition.

Combining the above methods, it should be easy to shoot this effect.