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Author Topic: What is embedded in a Photoshop TIF file?  (Read 2115 times)
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« on: February 05, 2013, 02:36:44 PM »

Anybody know what is inside a Photoshop generated 16-bit tif file? Specifically, what kind of image is "embedded" in a Photoshop tif that allows other programs to read it, even if the tif contains multiple layers?

I've always thought the embedded image is an 8-bit jpeg, but recent experience testing some HDR programs implies otherwise. It appears that those HDR programs are able to extract a true 16-bit lossless image from a Photoshop layered tif.

In my tests, I fed two versions of an image to an HDR program. One was a 16-bit layered tif, one was a flattened jpeg, 8-bit, high quality. The image contained a smooth gradient, which easily shows the difference in the originals between 16-bit and 8-bit. No adjustments were applied in the HDR program, but the outputs showed significant differences. The differences indicate that the HDR program got true 16-bit lossless data from the layered tif.

I'm asking here because this may be the only photography forum left with experienced gurus who might know the answer. Google has given me lots of gory details about the history of the tif format and its specifications, but I can't find the answer I'm looking for. What is embedded?
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« Reply #1 on: February 05, 2013, 03:43:23 PM »

Adobe bought the rights to tif. They have documents on their website explaining it. Yes, it can have layers. Almost all RAW files are a ISO standard tif with compression and additional data wrapper like EXIF. That is why DNG converter works.
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« Reply #2 on: February 05, 2013, 03:54:40 PM »

Adobe bought the rights to tif.

Actually, they bought Aldus and inherited TIFF because of that purchase/merger. Aldus, MSFT, Kodak and others developed the TIFF file format.

As far as what is in a TIFF, yes, there are specs for TIFF-6 (the most recent revision) and can be downloaded here: http://partners.adobe.com/public/developer/en/tiff/TIFF6.pdf.

If you have a 16-bit TIFF image file with layers, there will be the layers as well as a flattened composite 16 bit version which is what 3rd party apps that use TIFF can access (in the event the app does't support layers). You can save a 16 bit TIFF with ether LZW or ZIP compression but it's specifically NOT JPEG. JPEG compression in a TIFF file is limited to 8 bit only.
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« Reply #3 on: February 05, 2013, 04:20:56 PM »

That is what I meant, I could not remember the name Aldus. The info is on the wiki page.

Tif is a great format.
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« Reply #4 on: February 06, 2013, 02:25:40 AM »

Anybody know what is inside a Photoshop generated 16-bit tif file?

You can download the freely available program 'tiffinfo' what lets you see all kinds of metadata stored in a tiff file. I ran it on an image and here is what I got:

TIFF Directory at offset 0x8 ( 8 )
  Subfile Type: (0 = 0x0)
  Image Width: 560 Image Length: 277
  Resolution: 240, 240 pixels/inch
  Bits/Sample: 16
  Compression Scheme: LZW
  Photometric Interpretation: RGB color
  Orientation: row 0 top, col 0 lhs
  Samples/Pixel: 3
  Rows/Strip: 78
  Planar Configuration: single image plane
  Make: PENTAX
  Model: PENTAX K-5 II s
  Software: Adobe Photoshop CS3 Macintosh
  DateTime: 2013:02:06 07:21:58
  XMLPacket (XMP Metadata):
<?xpacket begin="Ԫ" id="W5M0MpCehiHzreSzNTczkc9d"?>
<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="Adobe XMP Core 4.1-c036 46.276720, Mon Feb 19 2007 22:13:43        ">
   <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
      <rdf:Description rdf:about=""
         <tiff:Model>PENTAX K-5 II s</tiff:Model>
      <rdf:Description rdf:about=""
         <exif:Flash rdf:parseType="Resource">
      <rdf:Description rdf:about=""
         <xap:CreatorTool>Adobe Photoshop CS3 Macintosh</xap:CreatorTool>
      <rdf:Description rdf:about=""
      <rdf:Description rdf:about=""
         <photoshop:ICCProfile>sRGB IEC61966-2.1</photoshop:ICCProfile>
      <rdf:Description rdf:about=""
         <xapMM:DerivedFrom rdf:parseType="Resource"/>
<?xpacket end="w"?>
  RichTIFFIPTC Data: <present>, 64 bytes
  Photoshop Data: <present>, 10784 bytes
  EXIFIFDOffset: 658496
  ICC Profile: <present>, 3144 bytes
TIFF Directory at offset 0xa0c40 (658496)
  ExposureTime: 0.005556
  ISOSpeedRatings: 100
  DateTimeOriginal: 2012:10:30 18:06:20
  DateTimeDigitized: 2012:10:30 18:06:20
  ShutterSpeedValue: 7.491853
  ExposureBiasValue: 0.000000
  MeteringMode: 2
  Flash: 9
  ColorSpace: 1
  PixelXDimension: 560
  PixelYDimension: 277
  CustomRendered: 0
  ExposureMode: 1
  WhiteBalance: 0


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« Reply #5 on: February 06, 2013, 03:08:37 AM »

That will make good bedtime reading. Wink Smiley

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« Reply #6 on: February 06, 2013, 03:37:22 AM »

That will make good bedtime reading. Wink Smiley
I think I'll wait for the film....   Wink
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