Mike Engles writes:

I would have thought that photographs taken by spacecraft are to be
viewed.

Not just viewed, measured. For that, you need to calibrate the camera
regularly, and preserve the data from it. For that, it's worth keeping
the data in linear form, and using more memory and transmission time.

It strikes me that if gamma encoding is necessary for terrestrial
imaging to maximise the use of a limited number of bits, then that would
also apply to space photography.

Generally no, because the tradeoffs are different. Some cameras *do*
allow you to save data in a linear losslessly compressed form called
"raw", precisely when you want more control over what's done with it.
If you have raw camera data, you can process it in 16-bit linear form if
you want.

There was a thread in the scanner
group, where the expert consensus was that any imaging,storage and
processing in a linear domain invited image degradation and
posterisation.

Any processing in *8 bit* linear invites posterization and other
degradation. Using *16 bit* per sample linear avoids most of this for
ordinary pictorial images. Using *floating point* linear is enough for
high dynamic range images. You must distinguish between these different
linear forms.

Yet we find that such linear imaging,storage and
processing is common in scientific digital imaging, where one would
imagine that extreme accuracy was paramount.

I'll bet it isn't 8 bit linear.

Do they use a large number of bits to avoid problems associated with
linear storage and processing? The expert consensus was that one would
need 18 to 20 bit linear images to match the efficiency of a 8 bit gamma
encoded image.

Yes, though the 18 or 20 bit number depends on what you mean by
"efficiency", and what intensity range you're trying to cover.

What is sauce for the goose is sauce for the gander.

Can't you see that 8-bit linear and 16-bit linear are entirely different
sauces?

Timo Autiokari has been saying for ages that scientific imaging was done
linearly. He has been abused soundly for his claims.

He's been abused for recommending 8-bit linear over 8-bit nonlinear.

We have been told
that no one who does serious image processing does it linearly.

Oh, who said that? I do the actual signal processing in linear space
(in 32-bit floating point), but often store images in 8-bit nonlinear
form. There's no contradiction here; it just requires a conversion.

So all
the scientists of the world who regularly do their processing in a
linear domain are not really serious and that they are merely FADISTS
like Timo Autiokari.

Again, they're not using 8-bit linear for any serious measurement data.

Dave