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19.2 Improving the acquisition / image quality 151
Figure 6: Image corrections: Host-based flat field correction
19.2.2 Optimizing the color fidelity of the camera
Purpose of this chapter is to optimize the color image of a camera, so that it looks as natural as possible on different
displays and for human vision.
This implies some linear and nonlinear operations (e.g. display color space or Gamma viewing LUT) which are
normally not necessary or recommended for machine vision algorithms. A standard monitor offers, for example,
several display modes like
sRGB , "Adobe RGB" , etc., which reproduce the very same color of a camera color
differently.
It should also be noted that users can choose for either
• camera based settings and adjustments or
• host based settings and adjustments or
• a combination of both.
Camera based settings are advantageous to achieve highest calculating precision, independent of the transmission
bit depth, lowest latency, because all calculations are performed in FPGA on the fly and low CPU load, because the
host is not invoked with these tasks. These camera based settings are
• gamma correction (p. 153)
• negative gain / gain (p. 153)
• look-up table (LUT) (p. 153)
• white balance (p. 156)
• offset (p. 157)
• saturation and color correction (p. 158)
Host based settings save transmission bandwidth at the expense of accuracy or latency and CPU load. Especially
performing gain, offset, and white balance in the camera while outputting RAW data to the host can be recom-
mended.
Of course host based settings can be used with all families of cameras (e.g. also mvBlueFOX).
Host based settings are:
• look-up table ( LUTOperations )
• color correction ( ColorTwist )
To show the different color behaviors, we take a color chart as a starting point:
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