[Kde-imaging] [Bug 204437] DNGConverter turns olympus ORF unusable

[Gustavo Claramunt]

https://bugs.kde.org/show_bug.cgi?id=204437





--- Comment #34 from Gustavo Claramunt <gclaramunt gmail com>  2009-08-25 10:30:28 ---
Maybe this make some sense...
After taking a  look to Adobe DNG Spec
(http://www.adobe.com/products/dng/pdfs/dng_spec_1_3_0_0.pdf, page 22) I can
see it uses BlackLevel 

(and other 3 related tags) in a different way than usual RAW files ... so the
problem is a little bigger.

Maybe dcraw/libraw/etc use algorithms to demosaic dng files based in adobe
specification, but in this case (don't know others) the value from 

BlackLevel is not suited to those calculations cause is a "different"
blacklevel (in spec pdf note a "mapping raw values to linear reference 

values") cause is taken directly from camera's raw.


Possible "global" solutions as far as i'm an ignorant :)?

1.-DNG Should not have exif data from original raw files than interfere with
the Adobe specs, so every tag in exif metadata from raw files 

should be converted u ommited if it make unconsistency with oficial spec (as
noted by Alex in comment #31).

2.-Every raw developer (dcraw/libraw/etc) should adapt to not use those
"duplicated" exif data when dealing with DNG files.

Drawbacks:
-In the first case, dngconverter and/or exiv2 should adapt/filter exif values
according to official dng spec.
-In the second case... too many software develovers should be concerned about
this issue... and maybe it isn't the correct methos cause we're breaking the
official dng specs... but who knows.

Notes:
-I've tested zeroing instead deleting the problematic "Olympus BlackLevel" tag,
resulting in "NO black/green" picture but not as good colour 

as when deleting the key (maybe related to Alex comment #33?)

- at Andreas, there are lot of discussion with DNG usage, take a look to Barry
Pearson "Defend DNG to the max" page at
http://barrypearson.co.uk/articles/dng/index.htm. In many cases, photographers
wants to retain their digital negatives as "intact" as they can. In my case
also want to be able to tag these negatives, fill xmp metadata, comments,
ratings, etc, AND store those valuable informations within the file itself so i
can see/use it in other softwares/workstations. With ORF i can only set
ratings/comments/tags, no way to modify anything else AND the
rating/comments/tags are stored into digikam database... so i can't see/use it
outside Digikam. That's my personal point about using DNG, but there ar more
out there :)

P.S.-One IMPORTANT thing i've noted (and posted at the begining of the bug
file): I have "tons" of .orf files which converted to dng WITHOUT the problem
mentioned here... but there are a bunch with the problem. Why sometimes right,
sometimes wrong? Well, i've guessed why:
When my camera takes a picture and the resulting ORF has a BlackLevel value of
(0,0,0,0), the converted DNG (with both DNG BlackLevel tag and Olympus
BlackLevel tag having the same value) works allright.
But the problematic raw files has a BlackLevel of (68,68,68,68) (in both
BlackLevel tags, dng and olympus)... Obviously, if i set both to (0,0,0,0) the
image displays without the nasty black/green, but the color balance/white
balance/black balance is not accurate.

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