exif-handling.txt 2.22 KB
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             How GIMP should handle EXIF data

                     Bill Skaggs 1/2/05

This is a summary of how an image editing program is supposed to
handle each of the EXIF fields, according to the EXIF specs.  Note
that this expresses my understanding based on a quick reading, and
should not be taken as gospel.  For details on the contents of each of
these fields, consult the formal EXIF specifications, available from
http://www.exif.org/specifications.html.

(Note: according to the EXIF specs, an EXIF jpeg file must have a name
that is ASCII, in 8.3 format, with extension .JPG, but of course we
are not going to enforce this.)



Fields that should be used to set up the GIMP image when an EXIF file
is loaded, either by using them to configure the image (e.g.,
orientation), or by placing them in parasites that can be accessed by
non-exif-aware functions.  

Orientation 
XResolution 
YResolution 
ResolutionUnit
ImageDescription 
Artist 
Copyright 
Colorspace
ComponentsConfiguration 
UserComment 
SubjectArea 
SubjectLocation
ImageUniqueID 
PixelXDimension 
PixelYDimension 



Fields that should be modified by GIMP when an EXIF jpeg file is
saved.  A letter "M" indicates fields whose presence is mandatory
according to the spec. 

Orientation 
XResolution (M) 
YResolution (M) 
ResolutionUnit (M) 
Software 
DateTime 
ImageDescription 
Artist 
Colorspace (M)
PixelXDimension (M) 
PixelYDimension (M) 
ComponentsConfiguration (M)
UserComment 
SubsecTime 
SubjectArea 
SubjectLocation 
FileSource
ImageUniqueID 
thumbnail Compression (M) 
thumbnail XResolution (M)
thumbnail YResolution (M) 
thumbnail JPEGInterchangeFormat (M)
thumbnail JPEGInterchangeFormatLength (M)  



Fields that should be used and saved related to color management:

TransferFunction 
WhitePoint 
PrimaryChromaticity 
YCbCrCoefficients
ReferenceBlackWhite



Fields that should be deleted if they exist when saving a file as
jpeg, because they only apply to uncompressed (TIFF) data.  This
applies both to the main image and to the thumbnail, if there is one. 

ImageWidth 
ImageLength 
BitsPerSample
Compression 
SamplesPerPixel 
PhotometricInterpretation 
StripOffsets
PlanarConfiguration 
YCbCrSubSampling



Any field not mentioned here should be passed through unchanged.