Another option would be to...

Not quite, though I didn't spell out what would be done. My fault there, sorry. The idea is to
step a single frame at a time in the movie projector, and capture that frame as though it was
a single still. It doesn't matter whether it's direct or a reflected image. You'd use an image
captre device, like a monochrome CCD, but since we're not playing the frames at regular speed,
the capture device can operate much slower and capture much more detail. The capture device
also wants to be as far from the projector as produces more useful detail.
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(This eliminates blur, allows you to get all of the detail of the frame, etc.)
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If it takes 1 second to capture a still at such high resolution, you simply forward to the
next frame about once a second, and each frame becomes photographable. (The BBC used similar
techniques to produce production stills from camera footage.)
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You do this once with red only light from the camera, then again with only green light, and
finally with blue light. Hence the use of a monochrome CCD. You get a higher resolution
capture, but also by blending the images, you end up with HDR stills. Not sure if there is an
animated version of OpenEXR, but there is a version of MPEG specifically for HDR. You then use
that to convert the stills into a movie.
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I'm probably still skipping details, but it's a variant on how they "clean" analog movies
(which is done frame-by-frame) and then use those stills to rebuild a full movie, originally
also on tape (so they had to burn a single frame onto a single celluloid window, with very
high accuracy).