Usability of Digital Cameras for Verifying Physically Based ...

Figure 22: A Bayer filter mosaic is a color filter array for arranging RGB color
filters on a square grid of photosensors [bay06].
and 1 Million for both red and blue filters. To recalculate a full 4 Megapixel RGB
image a color interpolation called demosaicing has to be done. This algorithm
estimates the missing RGB values by using information from the surrounding
pixels. After this step, various image enhancement techniques like white balance,
sharpening, contrast and brightness adjustments, noise reduction etc. are applied
to the interpolated sensor data. The final image is usually either saved in JPEG or
TIFF file format – JPEG format is more common because of the smaller file size
due to compression. Figure 24 illustrates the individual steps of image processing
done by camera software.
Most prosumer-grade cameras provide two forms of output data: the RAW
image data [SG06] and the final image (see figure 23). The RAW image data con-
tains the actual values of each CCD sensor element. The final image contains the
enhanced data and is usually converted to 8-bit and compressed with lossy com-
pression algorithms. If we want to use the final image for verification purposes
we have to have that in mind.
Most camera manufacturers have created their very own raw file format – the
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