DIGITAL CORNER
By Bob Dean
Megapixels and image
quality
The larger the number of mega pixels, the better
the image right? After all, when we all learned the basics of photography we learned
a few axioms. Lens quality was number one and then film grain which we could relate
to ISO film speed. Well, welcome to world of high tech. The number of pixels in
a camera's sensor is not a good indication of the ultimate image quality, nor
is the lens quality. The design engineers have added something a whole lot more
difficult to measure with a simple number. What is it? Software!
Pixels
are small light sensitive elements that convert light (photons actually) into
electricity (electrons). A series of filters on top of the sensor determines the
basic color information and then some electronic circuitry near the light sensitive
areas of each pixel amplify the signal and send it on to the micro computer chip.
There are some nasty characteristics of the electronic devices that convert light
to electricity. First, the smaller the pixel, the less efficient they are, meaning
it takes more photons to generate a given amount of electrons. This means smaller
pixels don't work as well in low light as do larger ones. Also the amount of surface
area that gathers lig! ht is reduced because space is needed for the electronic
circuits that amplify the signal. Worse yet, small pixels tend to generate more
noise proportionally than larger ones.
This is where we look to the software. Each camera manufacturer has developed their own image processing software that turns the electrical signals into an image. This software does an amazing amount of work in a very short time. Among other things, it has noise reduction algorithms, routines that integrate the signals according to color and the capability to smooth out the edges of pixels. Only a few companies make sensors and signal processing chips, but each major camera company has its own proprietary software. Not only that, but even in one company software can vary between camera models. The most important capability of the so! ftware is the noise reduction, as it is the most difficult thing to do well.
How does this impact the camera buyer? Well, when you are looking at point and shoot digital cameras, don't just go for the 5-6 MP. A 4 MP may give you a better image. Research the web and the magazine rack to get reports on image quality before buying. Also, the sensor pixels in digital SLR's tend to be bigger so the impact of noise is reduced and the image quality improved by most all camera company software.