Message-Id: <200112121730.fBCHUlo20516@sitelicense.arizona.edu> Date: Wed, 12 Dec 2001 10:25:30 -0700 From: Tim Au Yeung <mailto:ytau@UCALGARY.CA> Subject: Re: Photoshop: Problem parsing TIFF files [that are too big] To: mailto:IMAGELIB@LISTSERV.ARIZONA.EDU
<pre>
Hello Isaac,
Photoshop only supports images 2 GB in size with a maximum dimension of
30,000 pixels by 30,000 pixels. Even though your image is within size
limits, it exceeds the dimension limit. I'm not aware of a work-around aside
from using something else to split the image, opening the two halves in
Photoshop, doing the work and reassembling in something else. Or you could
look for an app that handles infinitely large images (has no maximum size).
As far as the TIFF specification goes, if you're reading the actual binary
data, you need to check the first two bytes before looking at anything else
as they tell you what byte order the file uses. Once you determine that, the
normal tag consists of a 2-byte field that indicates which tag, another
2-byte field that indicates the length of the value, then 8 bytes
representing the value itself. In the case of the BitsPerSample tag, the tag
is (hex) 102, is a SHORT value, and has a value of 8,8,8 for a baseline RGB
TIFF.
If you're interested, you can go on Adobe's site and download the PDF
containing the TIFF 6.0 specification or I could e-mail it to you if you'd
like.
Tim
--------------------------------
Tim Au Yeung
Manager, Digitization Initiatives
Information Resources
University of Calgary
voice: (403) 220-8975
e-mail: ytau (at) ucalgary.ca
> I was searching the web for information about a problem I've encountered,
> and I came across this list. It seems that there was a discussion related
> to my problem in Oct 1998, but the issue was never resolved. I thought
> perhaps someone could enlighten me.
>
> I'm dealing with a program that generates a handful of TIFF files.
> Unfortunately I didn't write the program and I don't have access to the
> source code. In any case, it seems that the TIFF's it produces are
> readable by Photoshop (5.5) only until they exceed a certain size.
>
> Example: I have here two TIFFs that have almost identical headers. One is
> 85 x 105 pixels, and the other is 85 x 43810 pixels. I don't know much
> about the TIFF spec, but... here are the relevant snippets of the header
> tags:
>
> ImageWidth: 85
> ImageLength: 105
> BitsPerSample: 0x00c8 (??? 24-bit should give 0x0018)
> StripOffsets: 300
> SamplesPerPixel: 3
> RowsPerStrip: 105
> StripByteCounts: 26775 (ie 85 x 105 x 3)
> filesize is 80,625 (ie 3 x StripByteCounts + StripOffsets)
>
> ImageWidth: 85
> ImageLength: 43810
> BitsPerSample: 0x00c8
> StripOffsets: 300
> SamplesPerPixel: 3
> RowsPerStrip: 43810
> StripByteCounts: 11171550 (85 x 43810 x 3)
> filesize is 11171850 (ie StripByteCounts + StripOffsets)
>
> Note that the StripByteCounts tag in the larger image seems to be
> calculated exactly as in the smaller image, yet the filesize does not bear
> the same relationship to the StripByteCounts value. It's almost as if the
> larger image only has 8 bits of color data per sample, as opposed to the
> smaller image, which clearly has 24 bits (ie 3 bytes) per sample.
>
> No problems with the small image, but on attempting to open the large one,
> Photoshop spits out "Could not open the document because of a problem
> parsing the TIFF file." Interestingly enough, even the large TIFF is
> perfectly readable in Microsoft's "Imaging for Windows" applet, but no
> matter what I do (resave, etc), I can't get the mailto:$*@#$! image to open in
> Photoshop.
>
> If anyone knows the technical details of TIFF formatting or has any useful
> advice at all, I would appreciate it very much.
>
> Thanks in advance.
> --Isaac K.
>
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