[Image-SIG] python PIL 16-bit tiff files

[Sebastian Haase]

On Tue, Apr 13, 2010 at 2:16 AM, Guy K. Kloss <g.kloss at massey.ac.nz> wrote:
> On Mon, 12 Apr 2010 23:32:32 Sebastian Haase wrote:
>> are you sure it makes even sense to save a 16-bit RGB image ? This is
>> not meant as an excuse for PIL to not support it,
>> but 16mio colors should likely be enough for any application (i.e.
>> 8bit per R,G and B)
>
> It does make sense. Absolutely! Maybe not if you are *just* thinking in terms
> of final output for an end user, but during the whole
> capturing/processing/manipulation phase one can reduce many artifacts
> introduced through rounding, etc. Also when images are touched up by changing
> lightness or contrast images tend to expose "banding" quite severely.
>
> This and other effects are also the background behind the increasing
> popularity of HDR (High Dynamic Range) imaging. Particularly in scientific
> imaging subtle differences are much preserved this way. And it looked like
> Dan's image is the result of a microscopic picture, or something like that,
> with low contrast. So it could strongly benefit from a change in lightness and
> contrast.
>
> Higher channel bit depth are important for these cases, and even more to keep
> up with needed capabilities for the future!
>
> Guy

I was talking only about the information content captured by
physically collecting photons from a film with very short exposure
times. That is, the "capturing" phase; for what you call the
"processing/manipulation" phase I would always convert to
single-precision float (numpy.float) if that fits into memory. This
way you are save if values get negative or intermittently very small,
for example.
I'm just a bit confused here, because I am used to collecting gray
scale images, not RGB images, (from a cooled CCD on a microscope).
Those I also save as unsigned 16 bit integers.
BTW, the original example image looked also pretty "gray" to me, could
you tell the scanner to use 16-bit gray, maybe then the (physical)
scanning quality might even be better - don't know, just wild guess...

Sebastian