IPTC data revisited

Sivakatirswami katir at hindu.org
Thu Jul 19 17:35:06 CDT 2007

Mark Smith wrote:
> On 19 Jul 2007, at 21:55, Sivakatirswami wrote:
>> Sivakatirswami wrote:
>>> I asked this once a couple of years ago, I will ask again:
>>> has anyone tackled reading and writing IPTC data to and from a JPEG?
> It's been mentioned on the list before, but it might be worth checking 
> out the open-source ImageMagick, if you haven't already.
> http://www.imagemagick.org/script/formats.php
> If you scroll to the bottom of the page, there seems to be support for 
> IPTC....

Right, i'll look into that again... I also downloaded the spec from 
adobe: you have
to be able to (and know how to) write to any particular image format... 
it looks
like a binary addition...

this is from the XMP specification for writing to the JPEG format:

(all mess up from clipping out of a PDF, you get the idea)

this is over my head, but seems doable since Rev can handle binary...


In JPEG files, an APP1 marker designates the location of the XMP Packet. 
The following table
shows the entry format.
IMPORTANT: Following the normal rules for JPEG sections, the header plus 
the following
data can be at most 65535 bytes long. The XMP Packet cannot be split across
the multiple APP1 sections, so the size of the XMP Packet can be at most
65502 bytes.
● JPEG File Interchange Format Version 1.02
● ISO/IEC 10918-1 Information technology - Digital Compression and Coding of
continuous-tone still images: requirements and guidelines.
● ISO/IEC 10918-4 Information technology — Digital compression and coding of
continuous-tone still images: Registration of JPEG profiles, SPIFF 
profiles, SPIFF tags,
SPIFF color spaces, APPn markers, SPIFF compression types and 
Registration Authorities
This specifies the format of APPn markers and the file interchange format.
Offset Field value Field name
(bytes) Comments
0 0xFFE1 APP1 2 APP 1 marker.
2 2 + length of
namespace (29) +
length of XMP
Lp 2 Size in bytes of this count plus the
following two portions.
4 Null-terminated
ASCII string
without quotation
namespace 29 XMP namespace URI, used as unique ID:
33 < XMP Packet > Must be encoded as UTF-8.
> Best,
> Mark
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Om shanti
(In  Peace)


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