Preview Image changes after timeshift in CR2

[Archive]

[Originally posted by niccei on 2007-04-13 12:26:07-07]

Hello,

I just tried out the exiftool and if works fine on changing the date on my images. Unfortunately the embbed preview changes after the timeshift. Comparing the original image and the processed one I noticed, that the PreviewImageStart Tag has been modified.

Before I run exiftool I get the 1056x1024 preview in a viewer like irfanview. After the timeshift the thumbnail (160x120) is shown.

exiftool -AllDates-=8 -v 109CANON\_MG_0901.CR2

======== 109CANON\_MG_0901.CR2

Rewriting 109CANON\_MG_0901.CR2...

  Editing tags in: ExifIFD IFD0 MIE-Doc MakerNotes PNG PostScript TIFF XMP

  FileType = CR2

  MIMEType = image/x-raw

  Rewriting IFD0

  Rewriting ExifIFD

  Rewriting MakerNotes

  Rewriting InteropIFD

  Rewriting IFD1

  Rewriting IFD2

  Rewriting IFD3

    1 image files updated

Before:

exiftool -PreviewImageStart 109CANON\_MG_0901.CR2_original

Preview Image Start             : 9728

After:

exiftool -PreviewImageStart 109CANON\_MG_0901.CR2

Preview Image Start             : 7514004

I did not find any hints on browsing the forum. Does any one know, how to prevent the exiftool from changing the offset?

exiftool is Version 6.86 running as windows executable.

Thank you in advance,

 Niclas

[Archive]

[Originally posted by exiftool on 2007-04-13 12:41:24-07]

Hi Niclas,

The location of the preview image in the data (previewimagestart) is
not significant.  When meta information is changed, the data may
move.  If irfanview is assuming a fixed offset for the preview image,
then this is a bug in irfanview.  The offset of the preview image must
be determined by reading the PreviewImageStart tag in IFD0.

You can see that the previewimage itself isn't changed by extracting it
before and after editing with:

Code:

exiftool -previewimage -b IMAGE.CR2 > IMAGE.JPG

You should send a sample edited image along with a bug report to
the irfanview developers and see what they say.

- Phil

[Archive]

[Originally posted by niccei on 2007-04-13 13:54:47-07]

Hi Phil,

thank you for the fast answer. I wrote a bug report for irfanview and wait for the authors reply.

Niclas