However, the above photosites only measure the quantity of light. To achieve color, photosites also need a way to distinguish and record values separately for each color.
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Color sensors work by capturing only one of several primary colors at each photosite in an alternating pattern, using something called a "color filter array" (CFA). The most widespread and successful CFA has been the Bayer pattern, which uses alternating rows of red-green and green-blue filters:
A necessary but undesirable side-effect of CFAs is that each pixel effectively captures only 1/3 of incoming light, since any color not matching the pattern is filtered out. Any red or blue light that hits a green pixel won't be recorded, for example.
The CFA also means that at any given photosite location, one color will be measured directly and the other two will have to be inferred. This process of intelligently combining photosites to produce full color pixels is referred to as "demosaicing" (or "debayer" within REDCINE-X PRO®), and happens during RAW development.
Note: the above diagram is a simplified example of demosaicing. Actual algorithms are typically more sophisticated, and may adapt depending on edges, texture or other image content.
However, demosaicing is less of a disadvantage than the above diagram might lead one to believe. Detail can actually be extracted very efficiently, in part because Bayer arrays have been a well-studied standard for over a decade. In practice, not requiring demosaicing would have improved resolution by roughly 20% - definitely noticeable, but not the improvement one might initially expect. See resolution vs. aliasing for one reason why.
Unlike color sensors, monochrome sensors capture all incoming light at each pixel regardless of color. Each pixel therefore receives up to 3X more light, since red, green and blue are all absorbed:
This translates into a 1 to 1.5 stop improvement in light sensitivity. This can also improve the appearance of noise when shooting under artificial light or other color temperatures which differ substantially from daylight.
Unlike with color sensors, monochrome sensors do not require demosaicing to create the final image. The values recorded at each photosite effectively just become the values at each pixel. As a result, monochrome sensors are able to achieve a slightly higher resolution:
Another benefit is that monochrome sensors typically have more predictable highlight clipping. With color, clipping can occur in just the red, green or blue channel, whereas with monochrome, clipping is an all-or-nothing process. In practice, this can mean that images will have a slightly higher usable dynamic range, especially when considering that monochrome shadow noise is typically less objectionable than with color.
In many ways, the advantages of monochrome sensors are very similar to traditional monochrome film: image noise is lower at equivalent ISO speeds, and resolution is higher. Such improvements in image quality can be critical when shooting video that might later be used for stills in print advertisements.
However, not all advantages will be realizable, depending on intended use. For example, those familiar with traditional black and white photography may want to use lens-mounted color filters to control scene contrast. This might include using a red filter with landscapes, since these normalize the otherwise stark contrast between blue skies and green foliage, while also enhancing local contrast within each region. On the other hand, color filters also reduce available light by up to two thirds, thereby offsetting any sensitivity gain from monochrome.
One should also consider whether the quality of a monochrome sensor outweighs the flexibility of a color sensor. One can always convert color into monochrome afterwards, for example. Furthermore, with color capture, any arbitrary color filter can be applied in post production to customize the monochrome conversion, whereas with monochrome capture, the effects of a lens-mounted color filter are irreversible. Overall though, when output flexibility isn't needed, proper monochrome capture will always produce superior results.
With the recent announcement of both the Pentax K-3 III Monochrome and the Leica M11 Monochrome, it seems the popularity of monochrome photography may be increasing. If anything, the amount of monochrome cameras on the market has now doubled. But you don't necessarily need to spend thousands of dollars to get one.
I will share all the ways you can currently get your hands on a monochrome camera, including all known monochrome camera models old and new. Plus, some cheaper alternatives at the end.
Image taken on my custom monochrome converted Pentax K-5 II
You can skip this section if you already know, but I felt like it would be helpful to briefly talk about.
Simply put, a monochrome camera is a digital camera that can ONLY shoot in black and white.
This is a physical change on the sensor, not just a digital filter. Of course, most cameras have black and white image filters and any image can be post-processed as black and white. This is different. The image IS monochrome from the instant it's captured into digital signal.
Actually, this is how (almost) ALL digital sensors work.
Luminance levels are recorded into digital signal. In order to determine color, a color filter array (CFA) is placed in front of the sensor. These are the red, blue and green pixels you may have seen in diagrams before, with each pixel getting one of those colors in a specific pattern (bayer pattern being the most popular). A software process called demosaicing determines the color of each pixel based on it's own values and the values of those around it. It's a really clever solution, and way more math than I will ever understand.
A monochrome sensor does not have a CFA on top, and does not run demosaicing.
Without a CFA, a monochrome sensor will capture more light (approximately +1.3ev in my experiments).
Without having to run demosaicing, a monochrome sensor output will contain more detail (sharper).
Image tone and curve will be different.
For example, the following images were taken with the same exposure values of the same subject under the same controlled lighting.
Histogram of normal Pentax K-5 IIs with CFA
Histogram of monochrome converted Pentax K-5 II
If you want to learn more, please visit our website Monochrome USB Camera.
The only three production monochrome cameras currently available are:
(the following are affiliate links. Purchases made through them will provide me compensation)
That's it.
You can see why these two new models are kinda a big deal.
The Leica M11 Monochrome is not yet available as of writing this article, but soon. The Pentax K-3 III will be produced in small batches, and will probably be contingent on success to continue being made.
Here are past models that can be found on the used market:
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Comment below if I'm missing any.
There are a few services that will remove the CFA from your camera and convert it to monochrome. I can't vouch for these services, but here are the few I've heard of.
Note that the service will typically cost into the thousand or thousands of dollars. And that's not counting your camera.
To get my Pentax K-5 II Monochrome converted I used a guy off of PentaxForums.com with the username of Medex He posts his services there. They are inexpensive compared to these professional services, but only offered for Pentax or Ricoh GR models.
Want to dabble in true monochrome sensor photography for less? Turns out there are a few smartphones with dedicated monochrome sensor cameras. There are plenty of reviews online about them, so read up. I haven't tried one myself yet, but seems like a fun option. They range from $50 for the older ones, to $1,000+ for the brand new high megapixel smartphones.
(below are affiliate links. I will get a commission if you make a purchase through them)
Drop a comment if you know of any I missed.
Some cameras use different types of filters/systems to gain many of the same advantages of a true monochrome sensor when shot in black and white. These are not truly the same thing, but are compelling and cool in their own right.
Sigma Foveon sensor cameras. Look up how a Foveon sensor works. It's pretty cool, and allows it to get some of the advantages of true monochrome sensors.
Pixii Rangefinder camera. This cool new camera uses software to negate the effects of the CFA when in a special monochrome mode for "true monochrome RAW files". This one seems gimmicky, and I'd love to try it out. I'm sure it does SOMETHING, I'm just wary of whether it makes any tangible difference, let alone is close to the real thing. I'm open to changing my mind one day :)
This is a possibility, but incredibly difficult. It's what I originally planned to do. I did all the research, but a cheap broken camera to test on, and quickly decided to just pay someone to do it for me.
But if you want to give it a go, here's the info I gathered.
From the many sources I've read, the people who successfully do this do the following:
Disassemble the camera down to the sensor.
Remove any IR/AA type filters. Depending on the camera the process will be different. Also, it may be destructive or non-destructive depending on the camera.
Use special chemicals to soften/remove the CFA off the sensor. So far I have found no one willing to disclose exactly what they used.
Use a soft but sharp edge object to scrap off softened CFA off the sensor.
Assemble everything back together and hope it doesn't break.
I mentioned earlier that I had my Pentax converted to monochrome. I made a video talking a little more about it that you can watch here. I also have a Flickr gallery that you can check out here.
Hope this helps you achieve your monochrome camera dreams :D
-james
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