Browsing a favorite blog today (kurzweilai.net) I was turned on to a company called Invisage who has created something called QuantumFilm and claims that this invention is a replacement for CMOS sensors in digital cameras. QuantumFilm is a substance not too dissimilar from traditional photographic film in terms of being a substrate, but rather than being the capture medium itself, QuantumFilm is painted on top of a silicon sensor that converts signals from the film into digital bits for image processing and presentation. Instead of silver halide grains, as in traditional photographic film, QuantumFilm contains Quantum Dots - nano-scale semiconducting crystals - to collect light and transmit a correlating signal to the sensor beneath. The advantage of this approach is an increased sensitivity to light.

In a CMOS sensor, light must pass through a maze of metal before interacting with the sensor which reduces the number of photons hitting it. In QuantumFilm, all of the light is collected by the substrate and an extraordinary number of quantum dots signal corresponding electric charges to the sensor resulting in both an increased efficiency collecting photons and a higher resolution. This breaks down the traditional resolution-performance barrier.

A photographer or cinematographer cares about resolution, of course, but a wise cameraperson cares about it only to a point. This is because our eyes are more sensitive to deficiencies of dynamic range than deficiencies of fine detail. Fine detail is great, but it means little if gradations between degrees of light and color are unnatural and distracting (except of course in cases of artistic intent). Part of the reason that most agree that analog film still looks better is that it has far superior dynamic range (although some modern digital cinema cameras are making great strides to close the gap). So at times, the race for higher resolution has been counterproductive because more pixels meant smaller pixels, each of which therefore captured less light which equated to a reduction in dynamic range.

So QuantumFilm addresses this problem by collecting more light with smaller photosites (each quantum dot being a photosite). According to their website, QuantumFilm is 4x as efficient at this. One must wonder, though, whether the nano-scale quantum dots are sufficient in efficiency to overcome the reduction in size. In other words, is the increased efficiency undercut by the reduced size? I unfortunately don't have enough detailed technical knowledge of sensor design to guess whether that's the case, but since the applications of QuatnumFilm currently seem to stress consumer and industrial imaging products - cell phone cameras, security cams, medical imaging, etc, - and not cinema or pro photo capture, my guess is that the stress is on increasing resolution (a metric that always tickles the marketing folks right) and not so much on increasing dynamic range. After All, putting a 10 Megapixel camera in a smartphone without reducing the image quality while simultaneously decreasing the cost (another touted benefit of QF) is a big win.

That doesn't mean, however, that there isn't a cinema or pro photo application for QuantumFilm. A hurdle may be dynamic range coupled with scale. Professional image capture isn't a slave to the miniaturization trend that other imaging, in fact most other technology, is bound to. The physics involved indicate that size of the capture plane is a key to controlling depth of field in an image and that's a very important tool in our box. Quantum dots, though, are nano-scale photosites that may not seem as effective a solution in my 35mm frame. Of course I'm sure they could be manufactured a bit bigger and spread out a bit more - possibly even at reduced production costs (doubtful, if not for the premium on specialty products, then just simply for the way the world works); but that diminishes the advantage of full light collection and may require filtration as is the case on current sensors.

One advantage of an increased number of photosites is the opportunity to synthetically produce high dynamic range (HDR) images. One common method of producing HDR photos is to "bracket" an image - to take multiple shots across a range of exposure values and then combine them during postprocessing. Software algorithms synthesize an HDR image from the lower-latitude images provided, and the photographer also exercises some control over the image. (If you're looking for examples of HDR photography done very well, check out photographer Trey Ratcliff at stuckincustoms.com). A suggested approach to increasing the dynamic range of digital cinema cameras is to do the same thing, but with the varying exposure values captured on multiple individual photosites simultaneously. Of course doing this through traditional photolithography is a challenge, particularly because we're working with very specific frame sizes in which manufacturers would have to adhere (capturing 5 exposures on a 35mm sensor at 1920x1080 resolution would require about 10 million, rather than 2 million photosites, give or take some depending on how you want to deal with color and interpolation), and of course would cost more.

Using a substrate of quantum dots smaller than CMOS photosites, and costing less to manufacture, may be the answer to this problem. Of course, with smaller dots, getting more exposure may mean introducing noise, but I'm sure that can be sorted out. And that kind of processing might be able to take place on the sensor, reducing the processing needed by other components of the camera, but now I'm getting into speculation.

The point here is that I've often wondered where things will go in digital cinema and photography. Film, lovely, warm, and romantic as it is, will eventually be replaced as the mainstream capture medium (this is already happening to a degree but I don't think it will totally go away for a long time), though digital capture isn't quite as good yet - it has its challenges to overcome. So I often wonder about the image capture of the future, and my speculations can be pretty wild (biotech cameras with the dynamic range of the human eye!). Here, in QuantumFilm, I see bleeding edge technology applied to the field I love most and I can't help but geek out about the possibilities.