While you can set the Color Matrix to VERY low Saturation if you just put in something like:
0,1 0 0
0 0,1 0
0 0 0,1
, it will still Contain Color Information, even if very desaturated.
See: forum.krontech.ca/index.php?topic=584.msg3673#msg3673
If it would be Possible to save Monochrome Files from a Color Camera, that would have probably need to be done on Firmware Level, tricking the Camera into thinking it has A Monochrome Sensor instead of Color.
Try to Contact Krontech Regards that, best to get into Contact with them about Stuff like that is usually to just Call them from my Experience.
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Best way to Reduce Filesize for H.264 is in my opinion to reduce the Bit per Pixel Setting. Lowest possible setting is 0.50 Bits Per Pixel, and Should Cut The Size of the Resulting File more than in Half. How much that however affects the Time Needed to save / Transfer the File via The Network on the Camera, I dont know if the Encoder itself is the Bottleneck here, or the Network Speed; you would need to have to test that for your self.
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Regards Reducing The Time for your whole Workflow, i dont know if i quite understand what you are doing / Trying to do with the Camera, but would it be an Option to Capture the HDMI Output of the Camera, to use for Long-Term Analysis, and just Actually Save the Highspeed whenever something Important Happens? Could speed up things way more than any Improvements in Save Speed just from Settings or Changing Media you save to...?