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Digital photography

Following are some of the issues I have with digital photography. It is a work in progress.


Colour filters

Here's a problem: You need to capture three simultaneous images to create a colour image (red, green, and blue), but you only have a single sensor chip. The solution is to cover the sensor with lots of little colour filters, a different one on each pixel. One pattern is called the “Bayer filter”, but there's a few variants.

It basically means that each pixel is only really collecting one colour - either red, green, or blue. The two other colours are derived from the surrounding pixels in a process called demosaicing. This is a process involving sophisticated methods of interpolation.

To be fair, colour film is somewhat like this on a microscopic level. The difference is scale. With sensors increasing in resolution, this difference is shrinking. Further more, it is conceivable that in the near future digital cameras could treat an ultra-high resolution sensor more like film i.e by resampling the large, noisy image down into a more workable size.

Dynamic range

Dynamic range is a measure of the range of brightness that can be captured in an image. It is a ratio of the brightest value to the darkest value. You might have seen it recently in regard to LCD TVs or monitors, but it applies to cameras (i.e the capture of light) as well as displays.

Digital cameras have traditionally had pretty poor dynamic range. This is a problem because when a pixel on a sensor hits 100%, there's not much that can be done. You don't know if it only just hit 100% (e.g a white piece of paper) or if the light is much, much brighter (e.g the sun). Film doesn't act like this. Film, especially print (negative) film, has what's known as a “soft shoulder” in its response curve. The bright light is “compressed” into the upper end, allowing some detail to remain.

Digital imaging is improving however. In particular, Fujifilm has developed its “Super CCD SR” sensor. It adds small photo-diodes in between larger ones, which collect less light and are thus able to record detail in bright light. This extends the high end of the sensors' dynamic range.

Long exposure

to do


Digital photography fundamentally changes the role of the camera in the process of taking a photo.

Film cameras, even the most advanced ones, are still basically a light-tight chamber for exposing film - the lens goes on the front, the film goes in the back, the shutter stops light hitting the film before you want it to, and if you're lucky, you get a viewfinder and TTL light metering.

Digital cameras may look very similar, but there's one important difference - the camera is now the part that records the photo, not the film. This means that when you buy a digital camera, it's only going to become obsolete. New cameras will come along with newer, better sensors - more megapixels, less noise, or some other set of new tricks. Your camera might otherwise be very good, but the only way to get a new sensor is to get an entirely new camera.

It hasn't even been ten years since digital photography really hit the mainstream, but already the trail of obsolete digital cameras is huge. Major new models come out every year or two, far more often for the consumer P&S type.