Usability of Digital Cameras for Verifying Physically Based ...

specifications of these formats are usually not publicly available. However, some
RAW converters, e.g. dcraw [raw06a], also provide raw CCD data as output.
The errors that are introduced by the camera software can be avoided by us-
ing the raw CCD data. Unfortunately, this data cannot be compared to a rendered
RGB image directly. It just contains information about how much light passed
the filter but there is no information about how this relates to an XYZ or sRGB
value. The reason for this is that most digital camera spectral sensitivities are
not linear transformations of average human visual systems’s spectral sensitivit-
ies. Therefore, the camera and a standardized human observer do not “see” color
identically. Thus, a camera may generate two different sets of RGB values at two
color samples, while to a human observer they look the same. This is the most
severe problem we have to deal with when using a prosumer-grade digital camera
for color measurements. Because of the different spectral sensitivities it is not
possible to get an exact match between colors seen by a camera and a human ob-
server. This thesis will discuss how a prosumer-grade camera can nevertheless be
used for verification purposes.
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