page_title: Photographic filter
section_title: Contrast enhancement
hierarchical_section_title: Photographic filter / Uses / Contrast enhancement
caption_attribution_description: English: The effect of using polarizer and red filter in black-and-white photography.
context_page_description: In photography and cinematography, a filter is a camera accessory consisting of an optical filter that can be inserted into the optical path. The filter can be of a square or oblong shape and mounted in a holder accessory, or, more commonly, a glass or plastic disk in a metal or plastic ring frame, which can be screwed into the front of or clipped onto the camera lens.
  Filters modify the images recorded. Sometimes they are used to make only subtle changes to images; other times the image would simply not be possible without them. In monochrome photography, coloured filters affect the relative brightness of different colours; red lipstick may be rendered as anything from almost white to almost black with different filters. Others change the colour balance of images, so that photographs under incandescent lighting show colours as they are perceived, rather than with a reddish tinge. There are filters that distort the image in a desired way, diffusing an otherwise sharp image, adding a starry effect, etc. Linear and circular polarising filters reduce oblique reflections from non-metallic surfaces.
  Many filters absorb part of the light available, necessitating longer exposure.
context_section_description: Colored filters are commonly used in black and white photography to alter the effect of different colors in the scene, changing contrast recorded in black and white of the different colours.  For example, a yellow or, more dramatically, orange or red, filter will enhance the contrast between clouds and sky by darkening the blue sky. A deep green filter will also darken the sky, and additionally lighten green foliage, making it stand out against the sky. A blue filter mimics the effect of older orthochromatic film, or even older film sensitive only to blue light, rendering blue as light and red and green as dark, showing blue skies as overcast with no contrast between sky and clouds, darkening blond hair, making blue eyes nearly white and red lips nearly black. Diffusion filters reduce contrast in addition to softening resolution.
caption: Effects of using a polarizer and a red filter in black-and-white photography
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