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February 2000
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2000.02.02 21:35 "Re: Microsoft Imaging and Jpeg in TIFF", by <apex@calpha.com>
Hello,
I will tell you some things about Wang TIFF/J images.
One is that they use the "OJPEG" tags
JPEGInterchangeFileOffset(TIFFTAG_JPEGIFOFFSET) and JPEGInterchangeFileLength
(TIFFTAG_JPEGIFBYTECOUNT). What this is the the beginning of the JPEG stream.
Add to this the contents of each strip, raw, and there is the complete JPEG
data stream.
Or is it?
I was doing some research as I wasn to extract only a valid JPEG data stream
from a Wang TIFF image. So the procedure described above gets what appears to
be a JPEG data stream, starting with FF'D8' marker and ending with FF'D9'.
This data stream, even with an attached JFIF header, is not viewable in other
regular softwares (browser, PSP) nor valid as a PostScript DCTDecode stream.
Below is a short dump of this JPEG data stream, sans JFIF marker:
Image #01: SOI @ 000000
EOI @ 00C5E7
----- [ Structure Analysis of file: 101020.jpg ]-----
000000 : --- Marker
Start of Image 01
000002 : --- Marker
Comment: WANG<
00000C : --- Marker
Define Quantization Table(s)
Lq = 0043 - Quantization Table Definition Length
Pq = 0 - Quantization Table Element Precision
8-Bit elemental precision
Tq = 0 - Quantization Table Identifier
000051 : --- Marker
Baseline DCT - Non-Differential Huffman Coding
Lf = 000B - Length of the Frame Header
P = 08 - Sample Precision
Y = 07C8 - Number of Lines in Source Image
X = 04F8 - Number of Samples Per Line
Nf = 01 - Number of Frame Components
00005E : --- Marker
Define Huffman Table(s) - Huffman Table Specs
Lh = 001F - Huffman Table Definition Length
Tc = 0 - Table Class is: Lossless Method
Th = 0 - Huffman Table Identifier
00007F : --- Marker
Define Huffman Table(s) - Huffman Table Specs
Lh = 00B5 - Huffman Table Definition Length
Tc = 1 - Table Class is: AC Table Method
Th = 0 - Huffman Table Identifier
000136 : --- Marker
Start of Scan
Ls = 0008 - Scan Header Length
Ns = 01 - Number of Image Components
Values below are in decimal:
Cs_[1..1] = Scan Component Selector
Td_[1..1] = DC Entropy Coding Table Selector
Ta_[1..1] = AC Entropy Coding Table Selector
Ss = 00 - Start of Spectral or Predictor Selection
Se = 3F - End of Spectral Selection
Ah = 00 - Successive approximation bit position high
Al = 00 - Successive approximation bit position low
00C5E7 : --- Marker
End of Image 01
So, I wonder if some of these values are misnamed, or otherwise invalid, or of
it is an ISO specification valid JPEG data stream that other softwares view
not.
I have not tried to open this stream using libjpeg 6b, I think that would be
something to try to see if valid data could be garnered without hack from this
Wang "JPEG" data stream.
Whether this behavior is changed in some present version of Eastman
Software/Wang imaging, I do not know and do doubt.
I am interested to hear what others think of this. I will hack more on this
JPEG data stream, perhaps it is only I have misordered the tags or strips or
something, simply reading them.
I am hoping some JPEG expert will tell us the error, or not, of Wang's ways, or
even better, the Wang engineer should explain.
Andy
Myers, Randall wrote:
> Some time ago there was a discussion here about the fact that Microsoft
> Imaging (Wang Imaging) had implemented Jpeg in TIFF that did not conform to
> technical note 2 or was in some other way broken. Can anyone tell me
> whether these problems are corrected in the most recent (Kodak) version of
> Microsoft Imaging?
>
> Thanks,
>
> Randy Myers
> Healthcare Imaging Applications Development
> Data General
> randy_myers@dg.com