|Sigma DP3 Merrill. This is one of the cameras that's supported by Sigma Photo Pro's monochrome mode.|
Over the past year, we've seen some interesting dedicated black-and-white cameras that have been introduced by Leica and RED. These are very high-end cameras, and the RED camera is part of that company's DSMC (Digital Still & Motion Camera) philosophy.
As you may know already, the image sensors in our digital cameras are really black-and-white sensors. To create color images, most manufacturers apply a grid that has red, green and blue filters over the image sensor so that each photosite (or pixel) will record that color information. The camera's onboard processors then decode the information and use some very clever interpolation algorithms to assemble a full-color image.
Dedicated black-and-white cameras like the Leica M Monochrom do away with the Bayer filter and its accompanying onboard computational requirements. Each photosite on the sensor in the Leica M Monochrom records luminance values only, and because the camera doesn't have to interpolate to build color information, the images are inherently sharper than color photographs from a digital camera.
Bayer filter arrays can't be removed from or "turned off" in the camera. They're physically mated to the sensor, so even if your camera has a monochrome mode, it's still going through the whole process of building a color image, which is then being desaturated.
So if you want to shoot black-and-white photos, your options are limited. You can use your camera's monochrome mode, or shoot in color and process the images to black-and-white in the computer, or purchase one of a few dedicated black-and-white cameras, which are very good at what they do, but also quite expensive ($7,950 estimated street price for the Leica M Monochrom, body only).
In early 2013, Sigma gave us another intriguing alternative that's sort of a hybrid of all of those alternatives. In their Photo Pro software—Sigma's image-processing software for use with their cameras—the company came out with a monochrome mode that works with the Sigma SD1, SD1 Merrill, DP1 Merrill, DP2 Merrill and DP3 Merrill cameras.
Sigma is the only camera maker to use the Foveon X3 sensor. Instead of employing a Bayer array, the Foveon sensors capture full-color information at each photosite. Here's how Sigma describes the way it works: "...the Foveon X3 Direct Image Sensor utilizes the characteristics of silicon to absorb shorter wavelengths (blue) near its surface and longer wavelengths (green, then red) at deeper levels." If you're shooting RAW with one of the Sigma cameras that's supported by Photo Pro's monochrome mode and you convert the photo to black-and-white, you're not just desaturating a color-interpolated image. There was no Bayer array and its associated interpolation to begin with so the black-and-white conversion of the Sigma RAW file is more like shooting with a dedicated monochrome camera than a standard black-and-white software conversion. Images are sharp and crisp, and they exhibit smooth tonal transitions.
You can find out more about the monochrome mode in Sigma's Photo Pro software at www.sigma-photo.co.jp/sppmonochrome/en/introduction.html.