Hi Phil
Ok ... This one is complicated.
Data is 32x16Bit Words.
The known algorithm for calculating CRCs works like in Tag 0x0119.
Word;
[01] is CRC over odd Bytes of data (Byte 5-60)
[02] is CRC over even Bytes of data (Byte 5-60)
[31] is CRC over Bytes 5-32
[32] is CRC over Bytes 33-60
On the Data Bytes 5-60:
Shooting without lens you can see only three words with data and the rest is all zero.
Those three look like some other CRCs to me. They are too unsteady for regular data.
But the usual algorithm for CRC doesn't work here.
[03] unknown CRC
[08] unknown CRC
[14] unknown CRC
They divide the data into three parts.
1st Part Word #4-#7
2nd Part Word #9-#13
3rd Part Word #5-#30
most of the words look like params in the known form.
except words #5 #12 #15 #17 #18
They don't vary on zooming.
Word #15 is always integer 256; equivalent to the Flag in Tag 0x0119.
Word #12 is always the full radius N(1.0) as integer.
Dividing the other words by this radius N1 you get:
Word #05 radius N2
Word #17 radius N3
Word #18 radius N4
usual on MFT-sensor cams
N1 1.0
N2 0.83333
N3 0.66666
N4 0.33333
Cams with smaller sensors and more need of corrections can get
N1 1.0
N2 0.75
N3 0.50
N4 0.25
or
N1 1.0
N2 0.50
N3 0.3333
N4 0.1625
I'm sure that those 4 Integers are all radi dividing the Lens into 4 zones of different strength and character of corrections.
And compared with this, Tag 0x0119 is an older simple version wich is only a single linear correction from center to Radius N1.
And when I modify Tag 0x0119 with an Hex-Editor to completely zero ... my GX-8 ignores that and can save a fine full corrected Jpeg out of an RW2-File.
But when I modify something on Tag 0x011B ... then inCamera RAW-Processing doesn't accept the file and stores nothing.
That's another reason why I don't think that one Tag is correcting CA and the other is correcting Distortion.
_Both_ correct CA _and_ Distortion and the older 0x0119 in a simple way and the newer 0x011B in an complex way for modern lenses.
Newer Cams like GX-8 have both Tags but use only Tag 0x011B.
Older Cams HAVE only 0x0119 and use this one.
And Tag 0x011A looks like an selector.
It's always 1 on old Cams only having Tag 0x0119. And it is always 2 on new Cams with Tag 0x011B.
Greetings from Germany
Klaus
Hi Klaus,
Thanks. I have a note from another source that 0x011b is a CA correction, but I'll take note of your findings as well.
- Phil
Hi Klaus,
Did you figure out some more about this tag since 2018?
It looks like a good candidate to implement Distorsion and CA correction on Panasonic MFT.
Someone has figured out out to decode similar fields for Olympus MFT:
https://github.com/darktable-org/darktable/pull/12760 (https://github.com/darktable-org/darktable/pull/12760)
Best