Question

I’m looking for a very specific piece of information. I could make this a rather detailed question I guess but I’d rather try keeping it short and to the point.
I need to acces a piece of meta data (exif information) from within a Photoshop filter plug-in. I have never dealt with exif data from within a Photoshop plug-in or without and the PS SDK documentation is of a form that leaves a lot of questions. I would eventually get there but was wondering if anyone here has done this before and could help me out with an example. I’d be very grateful for that…

What we need should be documented here in the SDK:

documentation/html/group___resource_suite.html
documentation/html/imageresourcessection.html 

The latter document says that the resource ID I need to retrieve the exif data is 1059 (decimal) and that accessing Exif data is supported since PS 7.0 which is good. But the SDK has no information (that I found) as to what you get, pointer? pointer to what? They just tell you to look at the exif spec. So do I get a pointer to the RAW binary exif data and if so how to I extract a field from that.

The specifications for the Exif data are here:
http://exif.org/specifications.html

As an example I’d like to get at this exif field:

Tag Name                            Field Name          Dec     Hex     Type  Count
Image title                         ImageDescription    270     10E     ASCII Any

Answer 1

EDIT: After a deeper research I’ve found the following (an excerpt from the documentation):

Document: Photoshop API Guide.
Argument: Callbacks.

The callback routines are organized into “suites” collections of
related routines which implement a particular functionality.

The suites are described by a pointer to a record containing:

1. a 2 byte version number for the suite,
2. a 2 byte count of the number of routines in the suite,
3. a series of function pointers for the callback routines.

You are interested in the Property suite.

Current version: 1; Adobe Photoshop: 5.0; Routines: 2.

Properties are identified by a signature and key, which form a pair to
identify the property of interest.

Adobe Photoshop’s signature is always ‘8BIM’ (0x3842494D).

The EXIF property is controlled by The Japan Electronic Industry Development Association (JEIDA) and Electronic Industries Association of Japan (EIAJ) which merged in Novemeber of 2000. The EXIF specification can be downloaded from their web site at the following location.

http://it.jeita.or.jp/jhistory/document/standard/exif_eng/jeida49eng.htm

GetPropertyProc( )

MACPASCAL OSErr (*GetPropertyProc) (OSType signature, OSType key, int32 index, int32 * simpleProperty, Handle * complexProperty);

This routine allows you to get information about the document currently being processed.

property name: propEXIFData 
id:EXIF 
type:complex (modifiable)
description:Camera and device data.

To recap I’ll write some juicy code:

GetPropertyProc getProperty = formatParamBlock->propertyProcs->getPropertyProc;
rc = getProperty(0x3842494D, propEXIFData, 0, &simpProp, &compProp);
if ( rc )   
    return;

GetPIHandleSizeProc getSize = formatParamBlock->handleProcs->getSizeProc;
int32 size = getSize(compProp);
if ( !size ) 
   return;

LockPIHandleProc lock = formatParamBlock->handleProcs->lockProc;
uint8* exif = (uint8 *)lock(compProp, false);
if ( !exif ) 
   return;