Color filters

Why black and white needs filters

The first photographic plates saw mostly blue and violet light, and almost no red. Grass and leaves came out as dark patches, a blue sky turned nearly as white as the paper, and the clouds in it disappeared. Later films saw every color, but they still saw blue more strongly than the eye does, so a sky stayed paler than it looked. A yellow filter evened that out.

The rule

A filter lets its own color through and holds the others back. In black and white, its own color turns lighter and the opposite color turns darker.

The apple shows both sides. With Red it turns almost white, and with Blue almost black. The blue cloth goes the other way: darkest with Red, almost white with Blue. Yellow sits in between. It holds back blue, so the apple gets a little lighter and the cloth a little darker.

Sky, foliage and skin

The same rule, applied to what is in most photographs:

No filter

Yellow

Red

Blue

How far a filter goes depends on the scene. A deep blue sky turns almost black behind a red filter. The sky in this picture is paler, so it ends up dark gray.

Monolith, 1927

In 1927 Ansel Adams photographed the sheer face of Half Dome in Yosemite on glass plates. He exposed one plate with a yellow filter. Then he pictured the photograph he wanted, with a dark, brooding cliff under a sky gone nearly black, and exposed the next plate through a deep red filter. That plate became Monolith, the Face of Half Dome. He told the story in his own books for more than thirty years, most fully in Examples: The Making of 40 Photographs (1983). The George Eastman Museum shows a print of it in its online collection.

The Color pad is a set of filters

MonoVibe’s Color pad puts these filters on one square. At the center no filter acts: red, green and blue count the same. At each label sits the pure filter: Red on the left, Green on the right, Yellow at the top, Blue at the bottom. In each corner two neighbors mix half and half: orange at the top left, yellow-green at the top right, magenta at the bottom left, cyan at the bottom right. Between those points the pad changes smoothly, so every position is a filter of its own.

The pad works live in the viewfinder, so you choose the filter before you press the shutter, as with film. Your library receives only the black and white picture. Your last shot can still be opened in the editor and given another filter, and so can any color photo from your library.

What happens to the exposure

A glass filter holds back part of the light, so film behind it needed more exposure: about twice as much for a yellow filter, four to eight times as much for a red one, depending on the filter and the film. This filter factor brought a neutral gray back to the gray it would have been without the filter, so that only the colors moved.

In MonoVibe the camera meters the scene in color, before the Color pad does anything, and moving the pad does not change the exposure. The pad’s three weights always add up to one, so a neutral gray, a white wall or a gray street, keeps its brightness in every position. What moves are the colors, against each other. A picture that consists mostly of the opposite color, such as a wide blue sky with Red, therefore comes out darker as a whole. That is the filter at work. To make it brighter, use the Tone pad, or the exposure compensation ⊕ when Exposure controls are on.

Where the comparison ends

The Color pad works like the color filters of black and white film, but not on the same thing. A glass filter acts on the light before it reaches the film. The pad acts on the three color channels of a photograph that has already been taken. So:

• —colors the camera recorded as the same stay the same; the pad cannot pull them apart
• —a channel that was overexposed stays overexposed; no filter brings detail back into it
• —infrared effects, like the white foliage some very deep red filters give on infrared film, need light the camera never recorded

MonoVibe does not copy any particular glass filter. It gives you the decision film photographers made, for the colors your camera captured.