Datasheet

3
■ CHIPS AND PIXELS
blue for each pixel. We, therefore, think of these pixels as being in three “channels”
(Red, Green, and Blue) simultaneously so that the complete image is recorded as three
different black and white (B+W) images that form the full-color version. This concept
will be important when we get to color correction.
The number and density of receptor sites on the chip determine the resolution
of detail. This pixel count is given as either dimensions, such as 4992×3228, or as a
total, such as 16 megapixels, where “mega” means million (totals are usually simpli-
fied to the nearest decimal). Therefore, an 8-megapixel chip has less resolution than a
12-megapixel chip. Professional-quality people photography can be done with cameras
delivering 8 megapixels or more of resolution. Pixel count can be manipulated after
the fact through mathematical calculations that interpolate new pixels from existing
ones, but the amount of image detail can never exceed the original resolution of the
chip. That being said, there is no reason for you to obsess over the number of pixels
available as a standard of quality. Movie posters have been made from images with
fewer than 6 megapixels, and the quality of those pixels in terms of lack of noise and
fidelity of color information is more important than the quantity used for photograph-
ing people.
Bayer Pattern Chips
The usual arrangement of red, green, and blue photoreceptors across a digital camera chip
surface is called a Bayer pattern. This regular pattern alternates green with red and blue so
that there are twice as many green pixels as there are red or blue. There are more green pixels
because green holds 60 percent of the overall image luminosity (lightness-darkness) in an RGB
image. The signals from adjacent pixels are averaged together using complex algorithms to
determine the overall color and interpolate this into each pixel in the image. Skin colors sit right
between the red and green filter frequencies used in most chip designs, and as it turns out,
calculating skin color correctly is difficult. In digital photography, skin color can end up being a
little too red. You’ll learn how to compensate for this later.
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