[IMAGING-180] strange offset of first Exif IFD value

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: Format: JPEG
• Assignee: Unassigned
• Reporter: Paul Hartmann
• Created: 03/Feb/16 00:29
• Updated: 03/Feb/16 00:30

Description

Adding GPS coordinates to a jpeg image creates a file with strange offset of first Exif IFD value.

The following snippet is used to add the GPS metainfo:

    public static void main(String[] args) throws Exception {
        final File inFile = new File("IMG_7250_small.JPG");
        File outFile = new File("IMG_7250_small-output.JPG");
        final TiffImageMetadata exif = ((JpegImageMetadata) Imaging.getMetadata(inFile)).getExif();
        final TiffOutputSet outputSet = exif.getOutputSet();
        outputSet.setGPSInDegrees(123, 34);
        try (BufferedOutputStream os = new BufferedOutputStream(new FileOutputStream(outFile))) {
            new ExifRewriter().updateExifMetadataLossless(inFile, os, outputSet);
        }
    }

Running jhead on the output file produces a warning:

$ jhead IMG_7250_small-output.JPG
Nonfatal Error : 'IMG_7250_small-output.JPG' Suspicious offset of first Exif IFD value

Indeed, the offset should normally be 8 (as in the input file) but is 0x4a=74:

$ exiftool -v3 IMG_7250_small-output.JPG
[...]
JPEG APP1 (258 bytes):
    0006: 45 78 69 66 00 00 49 49 2a 00 4a 00 00 00 05 00 [Exif..II*.J.....]

As far as I can tell, this offset is useless, wastes space and possibly breaks software that relies on the standard value "8".