Friday, May 13, 2005

Digital camera CCD sensor size de-mystified

DPReview has an article on CCD (charge-coupled device) sensor sizes and what they actually mean. My camera has a 1/1.8 inch CCD sensor. This seems to actually mean that the sensor area is 7.20x5.35 mm.
Type Aspect Ratio Dia. (mm) Diagonal Width Height
1/3.6" 4:3 7.056 5.000 4.000 3.000
1/3.2" 4:3 7.938 5.680 4.536 3.416
1/3" 4:3 8.467 6.000 4.800 3.600
1/2.7" 4:3 9.407 6.721 5.371 4.035
1/2.5" 4:3 10.160 7.182 5.760 4.290
1/2" 4:3 12.700 8.000 6.400 4.800
1/1.8" 4:3 14.111 8.933 7.176 5.319
2/3" 4:3 16.933 11.000 8.800 6.600
1" 4:3 25.400 16.000 12.800 9.600
4/3" 4:3 33.867 22.500 18.000 13.500
35 mm film 3:2 n/a 43.300 36.000 24.000

My camera's sensor area is rather small compared to that of a 35 mm film camera. The problem with a small CCD sensor size is that the actual sensors are teeny. This can affect picture quality, leading to noise and dynamic range problems. Wikipedia has a good article on CCD sensors in general.

Here's the approximate size of the CCD sensor in my camera (top) and a 35mm film camera (bottom):



Wikipedia's entry on dynamic range contains the following sentence dealing with this term from a photographic point of view:
Photographers use dynamic range as a synonym for the luminosity range of a scene being photographed; the light sensitivity range of photographic film, paper and digital camera sensors; the opacity range of developed film images; the reflectance range of images on photographic papers.
With respect to CCD devices, dynamic range would be the range of luminosity the device could capture. The human eye in general is much better at distinguishing between gradations of luminosity than CCD devices are at capturing them. Thus the disappointment one experiences when a photo doesn't "look like" what one saw. This disappointment is the opposite of the blissful ignorance of the person listening to mp3 audio or viewing an image with an attenuated colour range. In these cases, extra information that the human ear or eye can't discern is thrown out to save space.