December 8, 2008
My first digital camera was a gift from my parents upon graduating from university in 2004. Although I had previously been interested in film photography, I loved being able to take as many photos as I wished without worrying about film or processing costs. Moreover, I loved being able to immediately review the photo, allowing for the opportunity to adjust parameters to get the perfect shot. Four years and three digital cameras later, the photography bug still has a firm grasp on me (and my wallet!).
Did you know? The first commercially available digital camera was the 1990 black-and-white Logitech Fotoman. With 0.09 megapixels, it sold for $995.
Digital imaging is so pervasive that it's easy to forget that the technology has been commercially available for less than twenty years. Our cell phones, webcams, DSLRs (digital single lens reflex) and compact point-and-shoot cameras all use digital sensors to capture images. Unlike film, which undergoes a chemical reaction when exposed to light, digital cameras capture light and convert it into electrical signals. Digital image sensors contain an array of millions of bucket-like photosites (each corresponding to a single pixel) that collect photons, the basic unit of light. The relative number of photons collected by each photosite corresponds to the light intensity, which is converted into digital data by other components of the sensor. Photosites can only collect light intensity and not colour. To record colour, each photosite is overlaid with a filter such that it only allows one of the three primary colours of light - red, green, or blue — to pass through it. The true colour of a single pixel is then estimated by comparing the intensity of adjacent red, green, and blue photosites using a special mathematical process, known as a demosaicing algorithm.
Did you know? The standard colour filter follows a Bayer pattern (named after its inventor) and records 50% green, 25% blue, and 25% red as the human eye is more sensitive to green light, therefore finer detail can be obtained than if the filter treated each colour equally.
The properties of a camera's sensor play a large part in determining the quality of photos a camera will produce. Increasing the number of photosites (measured in megapixels) on a sensor increases the resolution, the amount of discernable detail of an image. However, increasing resolution without increasing the dimensions of a sensor results in smaller photosites, which also affects photo quality. Going back to our analogy of photosites being like buckets that collect photons, recall that empty photosites record black and completely saturated photosites record white. Smaller photosites fill up with photons more quickly than larger photosites for a given exposure. Therefore, at an exposure where a small photosite becomes saturated and records white, larger photosites retain colour in more gradations - this is called dynamic range. Moreover, given the greater surface area of larger photosites, photons are captured at a higher rate, increasing electrical signal and decreasing grainy image noise.
Did you know?This year, Hasselblad is introducing a camera with a 50 megapixel sensor that is double the size of the largest DSLR sensors. It is estimated to retail for $27,995 US!
Whatever kind of camera you have, go out, take photos and have fun! As the renowned nature photographer Ansel Adams once said, "The single most important component of a camera is the twelve inches behind it."
References and Links:
1) History of photography: film and digital
2) More on colour arrays and demosaicing
3) The megapixel myth—do more megapixels equal better quality
Michelle is a PhD student at the University of Toronto studying how synapses form using the microscopic worm C. elegans as a model organism. She enjoys photography, ultimate frisbee, and crafty projects.