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jziegler37
01-07-2003, 02:49 PM
To all:

Here is a summary of replies to a question I posed some time ago concerning
the lossless Huffman encoding of JPEG compressed images. I'm sorry for
taking so long, but I received numerous replies that took quite a while to
investigate. Thanks to all who gave suggestions.

My original query was:

Does anyone have source code for reading JPEG compressed images that they
would be willing to share. Specifically, I am looking for software that can
read the Lossless Huffman encoding. This is the default standard for DICOM
files. At present, I must go through a rather painful process of loading
the files into Osiris and saving them in an uncompressed DICOM format. This
is fine for the occasional file, but when I must convert 60+ images at a
time, it becomes very frustrating and time consuming. I frequently receive
DICOM files for analysis, and some of them are JPEG compressed. I have a
program that I wrote to convert a series of DICOM files into one AVS field
file. I would like to include source code for reading these compressed
files.

I have tried using "FreeImage" from SourceForge.net. It will read a variety
of compression formats, including numerous JPEG encodings, but the one that
it will not read is the Lossless Huffman. I am aware of a several available
libraries for reading DICOM files, but each one comes at a premium price.


Summary of replies:

Most of the replies referred me to the International JPEG Group (IJG) web
site (www.ijg.org). They have free source code for reading several JPEG
formats. Unfortunately, none of these are the lossless Huffman encoding.
In addition, I discovered that the JPEG portion of the FreeImage library is
largely based on the IJG software. Cornell University has a rather well
known version that can read the lossless encoding, but as noted on the IJG
web site "Caution: the Cornell coder is known to have bugs for 16-bit data."
>From what I have been able to determine, this is in fact true.

Other replies included references for MATLAB, a Java implementation
(http://dcm4che.sourceforge.net/), ImageJ, and more. These all proved to be
too great an effort to implement in my C++ code to justify the time and
expense. However, these might be of use for someone else.

After further investigation, I was directed to another application on
SourceForge.net (http://sourceforge.net/projects/xmedcon/). XMedCon is an
application for reading DICOM files and includes a lossless Huffman JPEG
decoder. As it turns out, this is the Cornell code with a few bug fixes.
Moreover, its format made it easier to use and test. Fortunately, after a
bit of debugging effort, I was able to produce a working decoder. For those
who need to be able to read such JPEG compressed images (or need any number
of other applications), SourceForge.net is an excellent source.

I hope that someone else finds this useful.

Thanks,

Jim Ziegler
________________________________
James M. Ziegler, Ph.D., P.E.
Ncompass Research, Inc.
5615 Belrose Drive
Houston, Texas, 77035-2609
jziegler@flash.net

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