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Thom Hogan’s Complete Guide to the Nikon D300
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between the “effective megapixels” and actual megapixel
count in an image that is produced: extra photosites along the
edges of the sensor array (white in the following illustration)
are there solely to provide data for the interpolation routine to
look at in order to calculate the pixels that end up at the edge
of your image (gray in following illustration):
Interpolation has several serious consequences:
• Green data are the most accurate
. Because the Bayer
pattern repeats green, the camera has more data from
which to make its guess. It also helps that the photodiodes
in the sensor are most sensitive to the green bandwidth.
Moreover, subtle differences in green values actually
make for larger perceived differences in colors, especially
skin tones (yes, there’s some green value in skin colors).
• Red and Blue data generate the most “noise.”
Since both
the red and blue photosites aren’t repeated in the Bayer
pattern, there are fewer of those color data points from
which to predict each pixel’s value. Worse still, when the
light hitting a red or blue photosite is low, noise becomes
a significant possibility in the photosite’s value (see
“Noise,” below). For example, you’ll sometimes see noise
in the red channel of a blue sky, or noise in the blue
channel for a skin tone. Since the blue photosites are the
least sensitive to light, indoor lighting can be a real
problem for a sensor, as very small amounts of blue
wavelength light is produced by incandescent lighting,
