Nikon Medata discussion

leegong · January 30, 2015, 10:48:01 AM

Hi ,all ,
According to firmware analysis , Nikon tag 0xBC seems to indicates NEF thumbnail :
bytes 0-3 : string for version ,
byte 4-5 : maybe width
byte 6-7 : maybe height
byte 8-11 : unknown
byte 12 - N : data payload

Leegong

Phil Harvey · January 30, 2015, 12:58:45 PM

Hi Leegong,

Can you tell me what model this is for so I can check some images?

- Phil

Hayo Baan · January 30, 2015, 03:15:59 PM

Interesting, this looks like a newer tag to me; the older Nikon cameras I tested this with (D3, D200) don't have the tag, but the more recent D4 has.

The tag seems to be 7700 bytes long each time with quite a lot of 0 padding. It would be interesting to know what is in those bytes

leegong · January 30, 2015, 11:28:25 PM

Hi , Phil , Hayo Baan ,
Tag 0xBC is found in D5100 firmware , size 0xD98 bytes , including version string .

leegong · January 31, 2015, 01:01:33 AM

Tag 0xBA is found in D800 firmware , but not found in D5100 .
byte0 == 0x49
byte1 == 0x31
byte2 == 0x0
byte3 = Vignettecontrol : 0 - off , 1 - on
if byte3 = 0 , then followed by 258 bytes 0x0
if byte3 != 0 , then followed by unknown data

EDIT : Tag 0xBC is found in D800 also , the size is 0x1E0C ,
different from 0xD98 in D5100 , but seems only the first 0x12DE bytes of data payload
are useful .

leegong · January 31, 2015, 01:49:30 AM

1 byte for tag0x8A , it is set by JPG encoding hardware engine after one YUV image
is encoded into JPG , it absolutely indicates sth related to JPG encoding , but i have
no idea about what it means exactly.

leegong · January 31, 2015, 02:11:25 AM

value for Tag0xA3 = enum{0 , 1} , it comes from bit5 of one byte,
each bit in this byte indicates one kind of status :
bit3 indicates GPS Auto Meter , : 1 On, 0 Off
bit2 indicates status of sensor cleaning
bit1 indicates status of Info Menu :0 - off , 1 - active

Phil Harvey · January 31, 2015, 07:02:14 AM

Thanks for the hints. I assume that this byte you are talking about for tag 0xa3 is found somewhere in the firmware, and not in the image metadata? If so, I guess we are only interested in bit 5. Any idea what it means?

- Phil

leegong · February 01, 2015, 10:34:23 PM

Sorry , Phil , i have no idea about meaning of tag0xA3 .

Did you get thumbnail in tag0xBC ? i think that byte8 of tag0xBC is bitdepth .

Phil Harvey · February 02, 2015, 07:10:13 AM

Hi Leegong,

I have looked at tag 0x00bc, but it definitely isn't a JPEG thumbnail. Also, if bytes 4-7 are width and height, then the image is very small (68x34 for the D5100). How is the image data formatted?

- Phil

leegong · February 02, 2015, 11:08:12 AM

Phil , sorry for my poor english , the "NEF thumbnail" i mentioned above
means RAW data .
In D800 firmware , width = 0x42 , height = 0x2C ( 66x44 3:2 aspect ratio) , bitdepth = 12 (0xC)

Phil Harvey · February 02, 2015, 11:18:46 AM

Typically, very small images like this in other cameras are used for segmented metering. Do you think this image could be used for exposure metering?

- Phil

leegong · February 02, 2015, 11:27:59 AM

There is other metering data generated by metering CCD , this thumbnail data comes from
main CMOS sensor , maybe it can be used for exposure metering in Liveview mode , but i'm not sure .
EDIT : For more info of Nikon firmware , please visit www.nikonhacker.com .

-Leegong

Phil Harvey · February 02, 2015, 11:39:59 AM

Thanks. And thanks for the link.

- Phil

leegong · February 03, 2015, 07:56:49 AM

Hi , Phil ,
Sorry , my fault , the URL above is wrong , here's correct URL : https://nikonhacker.com/

Regarding tag0x8A and tag0xA3 , if you have time and don't mind ,
could you please alter value of them , then open image with
Nikon capture NX2 or View NX2 , check if specific error info is rendered ,
if so , it'll be helpful for decoding them .

-Leegog

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Nikon Medata discussion