Monochrome Cameras

Thursday, 19 March, 2015

It’s a strange situation now - in the past monochrome (or B&W or panchromatic) photos were the standard images to be produced. You had a choice of…. B&W film and that was it!! B&W remained the mainstay of (particularly professional) photography right the way through to the 1970s. Whilst the idea for colour projection (and photography) dates back to James Maxwell in 1855, it wasn’t until the launch of Kodachrome in 1935 that there was a viable commercial product available… at a price. The 1970s was when colour finally decreased to “consumer” prices.

Since the 1980s we have had the rise of digital which works completely differently. Whilst film has 3 layers, each sensitive to different wavelengths of light, a digital sensor is inherently monochromatic….. it only records light (a greyscale value) incident upon the sensor. On top of the sensor sits a colour filter array (CFA) which filters either red, green or blue light. The arrangement of filters in the array is critical and typically a Bayer arrangement is used. This has 50% green, 25% red and 25% blue filters meaning that the sensor records a matrix (or patchwork) of values for different wavelengths of light - this single layer is then demosaiced in to three new layers representing red, green and blue light.

The obvious point is that, if you only want a monochrome image, what can you do? The digital sensor is inherently recording in a single layer. The sub-sampling employed by using the CFA requires interpolation to a colour image which, if you produce a B&W, means you then convert back to a single layer! Crazy!! One solution is to buy a monochrome camera - yes, at least one manfacturer now makes a B&W camera and thats the Leica M Monochrom. Nice camera, but a little pricey at £4,500. One alternative is to remove the Bayer array (debayer) from an existing camera - a few people appear to have done this but there are (as far as Im aware) no commercial services as it’s a risky business. The array is bonded to the sensor and you need to scrape it off, but clearly people have successfully completed the task.

Besides shooting in monochrome, what are the advantages? Well with no de-mosaicing process to go through the images should be sharper, a fact critical for photogrammetry where colour is less important. I think we’ll see more of this over the next few years.

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