NWA-PCUG Newsletter Article, February 2010
Power to the Pixels!
Written by Dave Christenson,
The digital photo guru and member of the Fox Valley PC Association, Illinois

deanholste (at) sbcglobal.net (click to email author)

This article has been obtained from APCUG with the authorís permission for publication by APCUG member groups; all other uses require the permission of the author (see e-mail address above).

I suspect that everyone reading this has at least one digital camera. What criteria did you use when buying it? Size, features, cuteness, need, impulse? Some or all of these? Maybe. But Iíll bet that two you definitely considered are price and pixel count. All other things being equal, low price and high mega-pixel count is good! Right? Not always. Iíll certainly go along with the low price bit, but letís think about the pixels a bit.

Why do we want more pixels? Obviously, because the picture, or image, is made out of pixels, the more pixels we have the more detail the image can contain and the greater we can enlarge it, or more cropping we can do. If we go beyond the capabilities of the count, we get whatís called pixilation, or, more informally, stair-stepping, where a diagonal line zig-zags. Also called, for obvious reason, ďthe jaggies.Ē So, why don't we necessarily want the most pixels possible for the price?

Well, everything in this world is a compromise, including us. We all make unnecessary noise, so do pixels. When light from the lens hits a pixel it puts out an electronic signal, proportional to the amount of light striking it. But, there is also a residual signal in a pixel, that is, a signal that it puts out whether or not light is hitting it. This is called noise. This is on top of the wanted signal, and the lower the brightness of the image, the greater the noise appears. Thus, it shows up more in photos taken in dim light. But itís always there, and in all cameras. It appears more obvious in areas of smoothness, such as sky, or human skin, and causes the image to look somewhat rough or granulated. (To those who are used to film, itís more or less the equivalent of grain.) Altogether, noise is something really undesirable.

Whatís the easiest way to reduce the amount of noise in a pixel? Easy, make it bigger! Now, do you see the conflict? If we make the pixels bigger to reduce noise, then we have to have fewer of them on a given size sensor. Or, we can have bigger sensors. This method definitely works, but at a price. A bigger sensor means a bigger camera, and a higher price. Large sensors are expensive, huge sensors ridiculously so. (A giant sensor or a new car, your choice!) There is software in cameras designed to analyze the noise and reduce it. It works, but it has limitations distinguishing between noise and signal. Software packages can be purchased at varying price levels to reduce noise, they help but donít cure the noise problem, if you want to get into that.

You would think that camera manufacturers, being aware of the problem, would design their cameras to have a reasonable compromise between sensor size and number of pixels. The designers could, but specifications are given by the marketing group, who are well aware that ďPixels sell!Ē So, what should you do?

Well, consider how you are going to use your photos. Are you going to print 16Ē x 20Ē photos on high resolution glossy paper? Are you going to crop out an itsy-bitsy portion of the center of the picture and enlarge it? If so, Iím afraid you will have to bite the bullet and get a larger sensor camera. But if you are taking photos of birthday parties, vacations, and get-togethers, and want to print them as 4x5ís or e-mail them, then I wouldn't be too concerned about pixel counts. Maybe cuteness is more important.

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