Digital Cameras: What is Bloom on Images?
Bloom images refers to a halo effect caused by extremely bright light in images. The effect is believed to be caused by the inability for lenses to focus perfectly. There is no way around bloom because it is a result of the physical nature of the science of optics in lens technology. However, it is only noticeable when the source of light is much brighter than what the exposure is set for.
Understanding Bloom Images
An example would be shooting indoors during the daytime with a window in your frame. Because your exposure is set for the light indoors, which is much less powerful than the sun, the window will be blown out and white. Due to the nature of lenses, the powerful daylight will bleed slightly out of the window frame. The light falls off quickly, but it is still distinct and noticeable.
Bloom is dependent on the lens (lower quality ones produce more bloom) and the intensity of the light. Because of this, you may find yourself in a situation where you want bloom in the image for artistic reasons, but are not getting it naturally. You can reproduce bloom in post production by isolating the area where the light is framed and then apply a blur effect.