Color filters in black-and-white photography change how scene colors translate into gray tones. A filter generally makes similar colors appear lighter and complementary colors appear darker.

Common example: a red filter can lighten skin tones and darken a blue daytime sky, making clouds stand out more.

This is most relevant with black-and-white film, where the filter is applied at capture. Different filter colors produce different tonal relationships depending on the scene.

For normal digital cameras, it’s usually better not to put colored filters on the lens. Since most digital cameras capture color first and convert to B&W later, you can get similar or better control in post-processing by adjusting the color channels during the B&W conversion. Using a physical color filter on a standard Bayer-sensor camera also cuts light, can increase noise, and may reduce effective detail. Auto white balance can also counteract the filter’s effect.

Exceptions include specialized cases such as infrared work or cameras modified for monochrome capture.

So: use color filters physically for B&W film, but for standard digital B&W, simulate the effect in post by controlling the channel mix.