Contrast filters are used in black-and-white photography to adjust how different colours in a scene are rendered on film. By darkening or lightening specific colours, these filters enhance tonal separation, control contrast, and help emphasize certain elements of the subject. For example, a red filter will darken blue skies and lighten red tones, producing more dramatic skies and stronger subject definition. Understanding and using contrast filters allows photographers to manipulate the visual impact of a scene, achieve more expressive black-and-white images, and maintain precise control over the tonal balance in prints.