[3dem] reference example file for MRC Mode 0

[Mike Marsh]

Hi all,

I want to add proper import-export behavior for MRC files to Dragonfly.
Dragonfly software doesn't natively support signed BYTE but I want to give
users expected behavior. What we do is convert from signed BYTE to UBYTE at
import, giving a native range of [0,255] and then we apply an invisible
offset of -128. Thus, whenever you ask the software what the intensity is
of any pixel by probing, or looking at the histogram, etc, it reports
values on the intended range of [-128,127].

When I load a Mode0 image in Dragonfly and try to decode the pixel
intensities, I get a sensible image range [-102,99], and the histogram
looks correct, but when Ioad the same image into Chimera, it reports a
range of [-42, 39].

I don't know why there is a discrepancy, but I could use a standard or
phantom image with expected known intensities so I can validate my reader.
Can anyone recommend a standard Mode0 image to use for this purpose? I'm
sure it doesn't exist, but I could use something like a SMPTE pattern with
known intensities, written in MRC format.

Thanks in advance,
Mike
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