22 ABSOLUTE BEGINNER’S GUIDE TODIGITAL PHOTOGRAPHY
FIGURE 2.7
Decrease green
by 50 percent to
achieve color
balance.The next step is to interpolate the CCD data. Interpolation is a mathematical
process of estimating a missing value by taking an average of known values at
neighboring points. The camera processor includes filter software that interpolates
these pixels to approximate the correct color for each pixel. The following grid pro-
vides a simple example of how this is achieved. Note that the pixel in the center
does not really exist. It is created using the color data in the pixels around it—a
drawback of the Bayer mask method.121242121The filter software then interpolates the red and blue data. The result is a rough ver-
sion of the color image with RGB values for every pixel.
Camera software then goes to work on the image, using an unsharp mask to recover
some resolution and then interpolate non-square pixels, resulting in something that
approximates the final image.
The actual processors in digital cameras are much better at removing artifacts and
pixelation. Each manufacturer uses different software to maximize the color and
detail available to the number of pixels in the camera CCD.
The drawback to this amount of processing is that detail is lost to compensate for
the mask. The loss of detail becomes noticeable along the edges of dark and light
areas, such as in this example of a building against the bright sky.