A Filter History
For anyone with an smartphone who’s young enough to not have grown up with film cameras, a “filter” means an effect that you apply in Instagram or Photoshop. It could be as simple as a “blur” filter, or as complex as a “vintage look” that applies a series of complex algorithms to an image, changing color, texture, exposure values, even adding borders and more.
But of course, that isn’t what a filter started as! Before digital, a filter was simply a piece of glass that you put on your camera lens (and it still is, of course) to create an effect. At its simplest, a filter could be a UV or Skylight filter which had minimal effect on the image and is mainly used as protection between your expensive lens and the elements.
Using Common Analog Filters
For B&W photography, color filters are quite common; whatever color filter you put on, those colors become lighter/brighter in the scene and their opposites become darker. So a yellow or orange filter will brighten skin tones, and a red filter will brighten red tones, while making blue skies almost black.
Other common filters are polarizers, which minimize reflection and can remove glare from the surface of water, a car’s windshield, or even the glare off of a wet leaf. (post continued on DxO's Blog; link below…)