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Tuesday, April 30, 2013

Misinformation: Camera Tech

Dedicated black-and-white cameras offering heightened resolution over color




An interesting fact about camera sensors is
that they actually capture image information in black-and-white only. Color information isn't extracted, but rather it's estimated through "demosaicing" the information that has been captured through a color-filter array. In a Bayer sensor design, found in most digital cameras, a checkerboard pattern of red-, green- and blue-sensing photodiodes allows only the red, green or blue channels of light information to pass through each respectively colored filter over each photodiode. There are twice as many pixels dedicated to green since that color channel is so much more prevalent over red and blue when viewing with the human eye. Sigma's Foveon sensor design, on the other hand, uses three layers of color-sensitive diodes to capture color information as it penetrates each layer, with red, green and blue photons achieving alternating depths on the chip thanks to differing wavelengths. Sigma fans say this results in much sharper resolution, especially noticeable in black-and-white conversions, because most of the incoming light is gathered by each photosite rather than being effectively bounced away as it is in a Bayer design.
 
Myth: Always Shoot In Color
 
All other things being equal, more light-gathering abilities will produce better imaging quality, and interestingly enough, there are now a few cameras on the market that are able to gather almost all of the incoming light information because they do away with the typical light-reducing filters over the sensor. This results in a black-and-white-only camera. The Leica M Monochrom, for example, is a full-frame digital rangefinder with an 18-megapixel monochrome CCD sensor. Thanks to the dedicated luminance-only sensor, it sports a maximum ISO of 10,000 over a top sensitivity of ISO 2500 in the almost identical Leica M9 (which also lacks an anti-aliasing filter). Leica claims a "100% sharper image" than the M9, as well. For medium-format shooters, Phase One offers the 39-megapixel Achromatic+ digital back, which incorporates a filterless version of the sensor from the P45+ back. It's available in two configurations, with or without an infrared IR cutoff filter. Adding an infrared filter keeps the bandwidth of light information within the visible spectrum, whereas the IR-less version is more suited to scientific applications. (Metering is improved with the IR filter.) RED Digital Cinema has released the EPIC-M with the 14-megapixel black-and-white Mysterium-X CMOS sensor. David Fincher used the EPIC-M (which stands for MONOCHROME) on Justin Timberlake's Suit & Tie video, and he's reportedly working to complete an entire dedicated black-and-white feature film with the cameras.

There are several theoretical advantages to a dedicated black-and-white sensor, though real-world results will depend largely on the total overall capabilities of the camera and optical system. Without a color filter, anti-aliasing filter and demosaicing, you're gaining a one-to-one ratio of incoming photons to outgoing photon information (relative to the capabilities of the photodiodes). Removing demosaicing also reduces artifacts from that process, like moiré, the tendency to see erroneous color and distorted lines that seem to overlap when viewing closely aligned, often parallel lines of detail. This most commonly can be found in striped clothing or buildings with repeating geometric shapes like bricks.

But noise reduction is potentially the biggest advantage to a dedicated black-and-white sensor. Chrominance noise is mitigated, obviously. Luminance noise is theoretically reduced, as well, simply because there are better light-gathering abilities at the sensor and hence a heightened signal-to-noise ratio. Also, luminance noise is often spread at the same relative frequency throughout an image so it's more evenly spaced and closely resembles film "grain," which can be desirable. Another reason that resolution is heightened is because noise also influences fine image details.

Remember, these components are each only one part of the imaging chain, and it's important to realize that imaging quality and sharpness are also heavily reliant on your choice of lens, shutter speed, focus, aperture and even if you're using a tripod or not. But black-and-white photographers are a dedicated bunch, and perhaps the biggest singular advantage to working with a luminance-only sensor is that it will force you to see the world in black-and-white as there's no room for error. You'll lose highlight recovery abilities that you have with color channel information (i.e., when highlights are overexposed, it's often in only one channel and the other two channels can be used to recover blown-out areas). Optical filters for black-and-white photography are also once again very important, as imaging programs use color channel information to render differing desaturation adjustments.


 

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