Ooh, right, the grayscale bit is an oversight in FBGrab, I'll fix that ^^.
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Right, so, yeah, grayscale field + ligl shenanigans.
You can probably double-check by enabling it via lipc, then strace'ing awesome: I suspect you'll see a fancy waveform_mode being requested, but since they're not actually supported, it ends up being a flashing frenzy ;p.
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EDIT: Updated fbgrab & fbdepth are now part of USBnet

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