This system works well. Every Canon, Nikon, Pentax and Sony DSLR uses it, as do all medium-format cameras except the Phase One IQ260 Achromatic discussed in this article—pro-quality color images, for sure. (Sigma’s digital cameras with their Foveon sensors use a different approach; see the sidebar.) The problem is that each pixel receives light of just one primary color, which cuts down on resolution (because a portion of the data at each pixel is interpolated) and sensitivity (because the filters absorb some of the light that would reach each pixel otherwise). And the demosaicing process creates moiré and exacerbates aliasing that occurs when a pattern in the subject or scene conflicts with the pixel grid of the sensor. If you convert one of these images to monochrome, you still have the problems of reduced resolution and sensitivity, as well as aliasing.
To reduce the moiré and aliasing problems, most sensors have an anti-aliasing (AA) filter, or optical low-pass (OLPF) filter, which reduces those problems by slightly blurring the image at the sub-pixel level. Obviously, this further reduces resolution.
For the monochrome specialist, there are a few dedicated monochrome digital cameras. These omit the Bayer filter grid, since color data isn’t needed, just luminance (brightness) data, and therefore eliminate demosaicing and its problems. So every pixel receives all the light possible, improving sensitivity, and every pixel provides luminance data—there’s no demosaicing process, further improving resolution. And since there’s no demosaicing, there’s no need for the resolution-reducing AA filter—further enhancing sharpness. These monochrome cameras provide increased pixel-level sharpness, enhanced contrast, smoother tonal transitions and increased sensitivity (higher ISOs). Their primary drawbacks are cost (they start at $7,950) and the fact that you can’t shoot normal color images with them. You also lose the ability to adjust each color channel independently, as you can with color digital images—there’s just one channel. So you have to use color filters over the lens to produce black-and-white film-style tonal adjustments. (In black-and-white, a color filter lightens objects in a scene of similar color and darkens objects of complementary color, hence yellow and red filters are used to darken blue skies and make white cloud formations stand out dramatically, and green and yellow filters are used to brighten foliage, etc.)
|Black-and-white infrared film records images by infrared radiation alone, or by visible light and infrared, depending on which filter you use over the lens. A popular effect is with a deep red filter—white clouds and healthy green foliage stand out dramatically against black skies.
The sensors in most DSLRs have a filter that blocks infrared radiation to keep it from unduly influencing the images, so you can’t readily do infrared photography with these cameras. With Sigma DSLRs, you can easily remove the infrared-blocking filter, allowing infrared photography. There are companies that will remove the IR filter from your camera’s sensor (which voids the camera warranty, incidentally) to permit infrared photography. The Phase One IQ260 Achromatic doesn’t have the IR-blocking filter, so you can do infrared photography with it as-is (using the appropriate red IR filter over the lens). You also can rent infrared-modified DSLRs.
Note that lenses don’t focus infrared at the same plane as visible light, so you must focus manually and adjust for the difference.
There’s a small, some may say elite, group of dedicated monochrome cameras. These aren’t models with gimmicky firmware changes or cosmetic additions. These are true monochrome-dedicated cameras that have been built from the ground up to shoot the very best black-and-white images possible. If that’s what you need, this elite group is where you want to look.
Leica M Monochrom
Leica has been producing its splendid M-series 35mm rangefinder cameras since 1954 and digital versions since 2006. Among the current digital models is the first 35mm full-frame monochrome digital camera, the M Monochrom, introduced in 2012. It features an 18-megapixel CCD sensor that was designed specifically for monochrome digital imaging with legendary Leica M-series lenses. The 35.8×23.9mm sensor delivers 14-bit uncompressed or losslessly compressed RAW (DNG) files measuring 5212×3468 pixels or lightly compressed JPEGs measuring 5216×3472 pixels. A special layout of microlenses atop the sensor helps produce uniform exposure and excellent sharpness from corner to corner. A special glass sensor cover blocks infrared radiation above 700nm.
Because there’s no demosaicing, the M Monochrom can provide a histogram of the RAW data. This is very useful, and much better than conventional Bayer-sensor cameras, which can only display histograms for camera-created JPEG images from the RAW data because it shows actual clipping points, not JPEG clipping points. The camera also allows you to apply toning effects to JPEG images in-camera.