Colorfulness is a non-technical term for the measure of how intense a specific color looks. It is related to saturation and chroma (Munsell). Colorfulness can simply be said to be the degree of difference between a color and gray. But what gray? Saturation on the other hand takes into account that all colors are not equally bright when fully saturated: For example blue is darker than yellow and red. Saturation thus means the colorfulness of a color in relation to its own inherent brightness. Laymen will find that the terms colorfulness, saturation and chroma are used synonymously. The more colorful a color is, the more vivid and intense it seems, while less colorful colors appear muted and closer to gray. When all color has been removed and saturation is 0, the image is called a gray scale image. There is an overlap between lightness and saturation in that a more saturated color appears lighter.

Lightness, also called value (Munsell) or tone, is defined as a colors placement on a brightness scale ranging from black to white. In the Munsell color space this scale is divided into ten equidistant steps. The term “lightness” has been incorporated into the HSL (Hue, Saturation, Lightness) and Lab color spaces. The term “value” is also used in the HSV (Huse, Saturation, Value) color space, but used differently than in Munsell. In HSV value ranges from black to not white, but to the fully saturated color. Paints can be made lighter or darker by adding white or black, but that also reduces saturation. “Tone” is an obsolete term that stems from darkroom photography to denote the lightness of a specific area of the print. Yet “tone” is still used in art where light and dark “tones” are built up with charcoal or similar drawing medium

In digital phtography lightness can be calculated simply as (r+g+b)/3. However, that does not take into account that green is brighter than red and blue darker than red. The relative brightness of the color channels is taken into consideration in the IUV color space, that calculates lightness like this: i=(76*r+150*g+29*b)/256. It approximately says that green is twice as bright as red and red is 2½ times brighter than blue.

In painting the term “tone” denotes an intermediate between gray and pure color. A mixture of pure color and white is called a “tint” while a mixture of pure color and black is called a “shade”. In reality tint and tone are not as simple a it sounds, because though they do not have color in themselves, when white or black are mixed with a color, the color changes hue. In other words, black in mixtures behaves like a blueish color. For example you get a darker greenish yellow if you mix yellow and black, not just as darker yellow. Similarly will an addition of white make a color appear colder.

In software you can digitally create tints and shades by converting from the RGB colorspace to IUV or Lab colorspace and alter the L (lightness) channel as described above. This will not alter the hue of the color as when you mix pigments with black or white.

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Photo retouching and white balance

White balance correction is to correct the light in a picture to white. To do this you must have a neutral in the image like a gray card or a white wall. Software can correct white balance, but not all software solutions are equally good.

The first thing you want to address, when you begin to retouch your pictures, is white balance. White balance refers to the color of the light and assumes that the optimal light color is white. Some shots, like sunset or candlelight, do not have white light, but usually an impression of white light is good.

Some use Photoshop’s auto levels to set white balance, but that is not ideal, since auto levels just sets the brightest pixels to white and the darkest pixels to black without considering the mid tones. But what if the lightest pixel in your photo is not white? Or what if you do not have pure black in the photo? (Most pictures have black areas, but the brightest pixel is rarely pure white).

The mid tones are the most important and to help set the mid tones correctly one adds a grey card to the photo when taking the photo. A grey card is a flat piece of cardboard or plastic colored an exact mid tone neutral gray. Ideally one has three cards: a black, a gray and a white. Photoshop’s levels adjustment panel has three color pickers for picking color: one for white, one for gray and one for black. By clicking the gray color picker on the gray card, one can set the mid tones to neutral gray. One can  only include a gray card in the image if one intends later to crop the picture.

If one doesn’t want a gray card in the picture, or if one doesn’t have a gray card at hand, one can later use dedicated software that analyzes the image and finds the color of the light and sets it to white. There are problems with such applications: what if there are no neutral areas in the photo to deduct the color of the light from? Some applications do not need a neutral in the image, but most do to get a good result.

If you work with RAW images, you will have found that the RAW converters normally come with a control for color temperature, meaning a slider to adjust the image cool or warm. But what if the color of the light is greenish as when you have taken a picture in fluorescent light? The cool-warm slider is good for regular incandescent light, but not for fluorescent.

Color correction controls are rarely good for correcting white balance, because the color adjustment will not just neutralize the gray card, but will also tone the picture in an undesirable way: usually the blacks get colored or the whites or both.

In short one needs some neutrals in an image to set white balance. A white wall or a piece of white paper will do well; preferably also a gray card for the mid tones.

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