Black and white photography is one type of Monochrome photography where each position on an image can record and show a different amount of light, but not a different hue. In this black-and-white case, the images are containing tones of neutral grey ranging from black to white.
Black-and-white photography is considered by some to be more subtle and interpretive, and less realistic than color photography. The images are not direct renditions of their subjects, but are abstractions from reality, representing colors in shades of grey. Black-and-white photography is considered by some to add a more emotional touch to the subject, compared with the original colored photography.
Color images can be converted to black and white on the computer using several methods, including desaturating the existing color RGB image so that no color remains visible (which still allows color channels to be manipulated to alter tones such as darkening a blue sky, or by converting the image to a greyscale version (which eliminates the colors permanently), using software programs like Photoshop. After software conversion to a monochrome image, one or more hues can replace the grey tones to emulate duotones, sepia, selenium or gold toned images or cyanotype, calotype or albumen prints.