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2005.08.26 03:20 "Re: TIFF Thumbnail", by Joris Van Damme
Katrina, Folks,
Joris wrote:
> If the file is under 1 megabyte in size, you may send it to my
> personal e-mail address, and I'll take a closer look.
Katrina has send me a file to look at... It is an extremely weird TIFF
if ever I saw one. Here's next a complete tagdump, and my comments on it
below:
File "P0000049.TIF"
Byte order: Motorola
Format: Classic TIFF
IFD Tree
Page 0 at offset 8
SubIFD 0 at offset 22724
SubIFD 1 at offset 22920
Exif IFD at offset 636
Page 1 at offset 4096
Page 0
Offset: 8
Next IFD: 4096
NewSubfileType (1 LONG): -
ImageWidth (1 SHORT): 1792
ImageLength (1 SHORT): 1200
BitsPerSample (3 SHORT): 8, 8, 8
Compression (1 SHORT): No compression
PhotometricInterpretation (1 SHORT): RGB
Make (22 ASCII): "Eastman Kodak Company"
Model (32 ASCII): "KODAK DC290 Zoom Digital Camera"
StripOffsets (1 LONG): 33776
Orientation (1 SHORT): 0th row is top, 0th column is left-hand side
SamplesPerPixel (1 SHORT): 3
RowsPerStrip (1 SHORT): 1200
StripByteCounts (1 LONG): 6451200
XResolution (1 RATIONAL): 192
YResolution (1 RATIONAL): 192
ResolutionUnit (1 SHORT): Inch
SubIFDs (2 LONG): 22724, 22920
33426 (0 LONG):
Copyright (33 ASCII): "(c) 1999 FlashPoint Technology "
33434 (1 RATIONAL): 0,0166666666666667
33437 (1 RATIONAL): 2,8
Exif IFD (1 LONG): 636
36867 (20 ASCII): "1999:07:13 06:04:43"
37377 (1 SRATIONAL): 6
37378 (1 RATIONAL): 3
37380 (1 SRATIONAL): 0
37382 (1 RATIONAL): 1,26
37383 (1 SHORT): 2
37384 (1 SHORT): 0
37385 (1 SHORT): 1
37386 (1 RATIONAL): 0
41493 (1 RATIONAL): 140
41495 (1 SHORT): 2
SubIFD 0
Offset: 22724
Next IFD: 0
NewSubfileType (1 LONG): Reduced-resolution version
ImageWidth (1 SHORT): 96
ImageLength (1 SHORT): 64
BitsPerSample (3 SHORT): 0, 0, 0
Compression (1 SHORT): No compression
PhotometricInterpretation (1 SHORT): RGB
StripOffsets (1 SHORT): 0
Orientation (1 SHORT): 0th row is top, 0th column is left-hand side
SamplesPerPixel (1 SHORT): 3
RowsPerStrip (1 SHORT): 64
StripByteCounts (1 SHORT): 18432
XResolution (1 RATIONAL): 72
YResolution (1 RATIONAL): 72
ResolutionUnit (1 SHORT): Inch
SubIFD 1
Offset: 22920
Next IFD: 0
NewSubfileType (1 LONG): Reduced-resolution version
ImageWidth (1 SHORT): 288
ImageLength (1 SHORT): 192
Compression (1 SHORT): JPEG ('old-style' JPEG, later overriden in
Technote2)
Orientation (1 SHORT): 0th row is top, 0th column is left-hand side
XResolution (1 RATIONAL): 72
YResolution (1 RATIONAL): 72
ResolutionUnit (1 SHORT): Inch
JPEGProc (1 SHORT): 1
JPEGInterchangeFormat (1 LONG): 23086
JPEGInterchangeFormatLength (1 LONG): 10689
Exif IFD
Offset: 636
Next IFD: 0
ExposureTime (1 RATIONAL): 0,0166666666666667
FNumber (1 RATIONAL): 2,8
ExifVersion (4 UNDEFINED): 2.10
DateTimeOriginal (20 ASCII): "1999:07:13 06:04:43"
DateTimeDigitized (20 ASCII): "1999:07:13 06:04:43"
ShutterSpeedValue (1 SRATIONAL): 6
ApertureValue (1 RATIONAL): 3
ExposureBiasValue (1 SRATIONAL): 0
MaxApertureValue (1 RATIONAL): 214748364,8
MeteringMode (1 SHORT): CenterWeightedAverage
LightSource (1 SHORT): Unknown
Flash (1 SHORT): Flash fired
FocalLength (1 RATIONAL): 0
MakerNote (1024 UNDEFINED): 1, 0, 1, 0, 0, 0, 4, 0, 69, 97, 115,...
FlashpixVersion (4 UNDEFINED): 1.00
ColorSpace (1 SHORT): sRGB
ExposureIndex (1 RATIONAL): 140
SensingMethod (1 SHORT): One-chip color area sensor
FileSource (1 UNDEFINED): Recorded on a DSC
SceneType (1 UNDEFINED): Directly photographed
Page 1
Offset: 4096
Next IFD: 0
ImageWidth (1 SHORT): 96
ImageLength (1 SHORT): 64
BitsPerSample (3 SHORT): 8, 8, 8
Compression (1 SHORT): No compression
PhotometricInterpretation (1 SHORT): RGB
StripOffsets (1 LONG): 4292
Orientation (1 SHORT): 0th row is top, 0th column is left-hand side
SamplesPerPixel (1 SHORT): 3
RowsPerStrip (1 SHORT): 64
StripByteCounts (1 SHORT): 18432
XResolution (1 RATIONAL): 72
YResolution (1 RATIONAL): 72
ResolutionUnit (1 SHORT): Inch
So, what's in there?
- 'Main image' is what is called 'Page 0' in the above tagdump = IFD 0
in main list.
- This IFD 0 has two SubIFDs, both marked with NewSubfileType tag value
'Reduced-resolution version', therefore a decoder should assume that
these are new-style reduced resolution versions of the 'main image'.
- This IFD 0 also has an EXIF child IFD.
- There's a second IFD in the main list, called 'Page 1' in the above
tagdump = IFD 1 in main list. The producer of the file is aware of the
SubIFDs tag, obviously, and this second IFD does not have the
SubfileType or NewSubfileType tag. Both are good indications that this
second IFD should be regarded as a separate page. However, upon visual
inspection, it is clear that this IFD 1 is actually another reduced
resolution version of IFD 0. Thus, the first two bugs in this file are
that pre-SubIFD notion of reduced resolution versions and post-SubIFD
notion thereof are mixed, and that a reduced resolution version is not
marked as such. There is no way software can detect this situation, thus
decoders are forced to incorrectly conclude there are two separate
independent pages in this file.
- 'Page 0' (= IFD 0 in main list) contains a tag with 0 values (33426,
haven't got a clue what it is). I haven't double-checked, but I believe
that is illegal according to TIFF spec.
- 'Page 0' (= IFD 0 in main list) contains EXIF tags. That used to be
common practice in the early days of EXIF, before they decided to move
all EXIF info in a dedicated private IFD. However, there is also such a
dedicated private IFD tag. Using both this old-style EXIF and new-style
EXIF on the same IFD, well, it's weird at the very least. Additionally,
some EXIF tags are only mentioned in image IFD, some other EXIF tags are
only mentioned in EXIF IFD. There are no contradicting tags though.
- 'SubIFD 0' (= first SubIFD of IFD 0) says BitsPerSample is 0, 0, 0,
and StripOffsets is 0. Both is of course complete nonsense. The number
of channels is consistent with Photometric RGB, though, and to add some
more weirdness the StripByteCounts value is set to 18432, which is
consistent with ImageWidth, ImageLength, BitsPerSample and Compression.
- 'SubIFD 1' (= second SubIFD of IFD 1) is compressed with the old-style
JPEG scheme. I've never seen that in anything but a single main IFD.
I've not (yet) been able to visually verify what it actually contains
since my code is a bit messed up right now. But anyway, the conclusion
with old-style JPEG should always be that it is illegal, breaks TIFF,
and is thus overridden by new-style JPEG-in-TIFF, specified in
specification supplement 2
(http://partners.adobe.com/public/developer/en/tiff/TIFFphotoshop.pdf).
> While parsing the thumbnail data through the API
> TIFFReadRGBAStrip, it had an error in TIFFRGBAImageOK
> that says "Sorry, can not handle images with 0-bit
> samples."
>
> I checked in AsTiffTagViewer, it displayed:
>
> BitsPerSample Short 3 (count) 8,8,8 (value)
The first refers to SubIFD 0, the second refers to Page 1.
Katrina, this is probably the single worst TIFF I ever saw. It will be
quite a challenge. Some of the stuff is impossible to decode properly
(for instance, it is impossible for code to deduce that IFD 1 is a
reduced resolution version of IFD 0). Other stuff will depend on the
ability of your code to recover from errors in smart ways (for instance,
SubIFD 0 will lead to a decoding error, and so will SubIFD 1 unless you
jump through hoops decoding the illegal old-style JPEG, and smart
decoders must allow proper decoding of IFD 0 even after possibly failing
on these reduced resolution versions). Yet other stuff is rather
arbitrary (for instance, should one use the EXIF info in the image IFD
in this situation, or the EXIF info in the EXIF IFD, or should one merge
these?).
Good luck! If you feel up to it, complaining to the vendor of the
software that writes these monstrous files is the responsible thing to
do. Feel free to use my above comments on the file if you decide to do
so.
Joris Van Damme
info@awaresystems.be
http://www.awaresystems.be/
Download your free TIFF tag viewer for windows here:
http://www.awaresystems.be/imaging/tiff/astifftagviewer.html