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To: Adam Jenkins <ajenkins@kalgoorlie.cs.umass.edu>
cc: tiff@sgi.com, mccoy@spinach.pixar.com (Daniel McCoy)
Subject: Re: (more than 8 bits) TIFF images 
Reply-To: Sam Leffler <sam@relay.engr.SGI.COM>
In-reply-to: Your message of "Thu, 05 Dec 1996 16:17:32 EST."
             <199612052117.QAA08132@kalgoorlie.cs.umass.edu> 
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Date: Thu, 05 Dec 1996 16:13:53 -0800
From: Sam Leffler <sam@hyla.chez.sgi.com>
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    To:  tiff@sgi.com
    Subject:  Re: (more than 8 bits) TIFF images
    Cc:  mccoy@spinach.pixar.com (Daniel McCoy)
    Date: Thu, 05 Dec 1996 16:17:32 EST
    From:  Adam Jenkins <ajenkins@kalgoorlie.cs.umass.edu>

    Daniel McCoy writes:
     > 
     > From: Claire.Rossignol@best.ms.philips.com
     > > The BitsPerSample required values for Grayscale and Palette-color 
Images are
     > > 4 and 8 according to the TIFF 6.0 Specification. Does it mean that 
TIFF does not
     > > support BitsPerSample values > 8 bits for these images ?
     > >  
     > > If not, do you know any viewing tool which is able to display 12 
bits-TIFF images ?
     > 
     > I use 16-bit TIFF images and have submitted changes to the shareware
     > xv viewer to display both 16-bit RGB and grayscale images.  I
                                        ^^^
    
    Notice in the original message, he's talking about Grayscale and
    Palette-color images, not RGB.  The TIFF 6.0 standard does support 16
    bit RGB images, and so does libtiff. However the standard doesn't
    support 12 or 16 bit Palette or Grayscale images, and I don't know
    whether libtiff does.
    
Come on folks, the TIFF spec is totally wishy washy in just about any
and every area.  The spec defines mechanisms by which a wide variety
of different format data can be stored in a file.  You can trivially
specify 12-bit, 16-bit, a gazillion-bit data of any different Photometric
interpretation (i.e. image type).  The issue isn't whether you can
specify or store this data, the issue is whether anyone can, or will,
read it back when you ask them to.  As is noted in the spec (or perhaps
just very common knowledge), if you have data >8 bits and <16 bits then
it is common practice to store the data as 16-bit samples.  Most anyone
that'll handle 16-bit color data will also handle 16-bit greyscale data.
Given that palette images are specified as N-bit indices into 16-bit
colormap tables I don't see why anyone would want or need 16-bit indices
for this sort of image.

libtiff is typically not the issue in handling any or all of this stuff;
the issue is the application that uses the library.  (Unless the above
reference is to the TIFFRGBAImage support, in which case please RTFM.)

         Sam


