Is Exif metadata always saved immediately after the JFIF header?
In JPEG files. Is exif metadata always saved as the first token? Or could it be between other markers?
The comment below is: "Other JPEG markers follow after the APP1 marker area." http://www.media.mit.edu/pia/Research/deepview/exif.html Is this confirmed?
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The specs (http://www.exif.org/Exif2-2.PDF) say that - yes - APP1 should come first, right after SOI (ffd8), but sometimes APP0 (JFIF) comes first, right before APP1. cannot be considered a correct use, since both JFIF and EXIF specify that the corresponding markers must immediately follow the SOI. But in practice, it turns out that such cases happen quite often, and graphic editors and viewers correctly interpret such "incorrect" hybrid files.
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There are two common types of JPEG files: JPEG / JFIF and JPEG / Exif.
Both qualifiers (JFIF and Exif) require their respective title to appear immediately after the SOI (Start of Image) marker.
In the case of JFIF, this is the APP0 token, in the case of Exif, this is the APP1 token.
Perhaps the JPEG / JFIF file with the Exif block is somewhere later in the file. I noticed this happens when exporting a JPEG / Exif file from iPhoto. iPhoto finishes converting it to a JPEG / JFIF file, but stores the Exif metadata somewhere later in the file.
However, aside from requiring the header for the appropriate file format to be first, there is no restriction on the ordering of other APP # token blocks in a file. Therefore, the Exif block can be executed at any position in the JPEG / JFIF file.
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