lau@umn-cs.cs.umn.edu (Patrick Lau) (04/03/91)
I have been looking for a software that performs JPEG compression, and I think it is called Alchemy. Does anyone know where I can get a copy of that, or any other JPEG software? Thanks in advance. -- ------------------------------------------------------------- Patrick Lau Computer Science Department lau@umn-cs.cs.umn.edu University of Minnesota ...!rutgers!umn-cs!lau Minneapolis, MN 55455
cag@mnemosyne.cs.du.edu (Chris Gantz) (04/03/91)
In article <1991Apr2.182508.24699@cs.umn.edu> lau@umn-cs.cs.umn.edu (Patrick Lau) writes: >I have been looking for a software that performs JPEG compression, and >I think it is called Alchemy. Does anyone know where I can get a copy >of that, or any other JPEG software? Thanks in advance. >-- >------------------------------------------------------------- >Patrick Lau Computer Science Department >lau@umn-cs.cs.umn.edu University of Minnesota >...!rutgers!umn-cs!lau Minneapolis, MN 55455 If there is software that performs JPEG compression could I also receive information on how I can obtain the software. I am on a Sun Unix platform Thanks in advance... -Chris (cag@aragtap.den.mmc.com) -- Chris Gantz Internet: cag@mnemosyne.cs.du.edu Dept. of Math & Computer Science cgantz@diana.cair.du.edu University of Denver cag@aragtap.den.mmc.com Denver, CO 80208 Grad. Student
lau@umn-cs.cs.umn.edu (Patrick Lau) (04/04/91)
Just want to say Thank You to all the people who responded to my search for JEPG/Alchemy. -- ------------------------------------------------------------- Patrick Lau Computer Science Department lau@umn-cs.cs.umn.edu University of Minnesota ...!rutgers!umn-cs!lau Minneapolis, MN 55455
pshuang@athena.mit.edu (Ping-Shun Huang) (05/27/91)
I was wondering if anyone here knew of any articles in journals/magazines or would be able to give a brief but lucid explanation of the compression algorithm being used by the JPEG standard. I've recently acquired a program for the IBM-PC called Image Alchemy which knows how to perform JPEG compression and compresses typically at 5:1 ratios for the sample .GIF images which I have fed into it (i.e. the JPEG output is 20% the size of the already-LZW-compressed bitmap). I am quite curious as to how it is doing this. What I am hoping for is not exact pseudo-code but an idea of what the algorithm tries to take advantage of in image-type data. The degradation in the images is just barely noticeable but only upon careful observation. An interesting observation about JPEG (or at least the particular implementation of it which I was using) was that it is the only compression algorithm I know of where decompression takes more CPU time than the compression did. This may have been a fluke, but it was true for all images I tried and the difference was a factor of two and not just a few percent. I am also curious about arithmetic encoding, about which I have not heard very much before joining this newsgroup. -- Singing off, UNIX:/etc/ping instantiated (Ping Huang).
spencer@eecs.umich.edu (Spencer W. Thomas) (05/29/91)
See Communications of the ACM, April, 1991. -- =Spencer W. Thomas EECS Dept, U of Michigan, Ann Arbor, MI 48109 spencer@eecs.umich.edu 313-936-2616 (8-6 E[SD]T M-F)
marcos@netcom.COM (Marcos H. Woehrmann) (05/30/91)
> > An interesting observation about JPEG (or at least the particular implementation of it which I was using) was that it is the only compression algorithm I know of where decompression takes more CPU time than the compression did. This may have been a fluke> , but it was true for all images I tried and the difference was a factor of two and not just a few percent. > The reason that the decompression times are worse then the compression times is that to convert from a JPEG image to a GIF image you have to do not only the DCT and other JPEG stuff, but also colour quantization and dithering (this is because JPEG is a true colour format and gif is a paletted format). If you convert from true colour -> jpeg -> true colour, the conversion is virtually symmetric. marcos -- Marcos H. Woehrmann {claris|apple}!netcom!marcos | marcos@netcom.COM Oh, I'm sure you've heard it all before, but remember it's not what you say, it's how you say it, and how much you're paid to do so, and besides who's listening anyway. No one, that's who, because it's all been said and done and done and done and done to death. Let's talk about art, said the fool to the idiot. --Lydia Lunch
lawrance@ncsa.uiuc.edu (David Lawrance) (05/31/91)
See also Rabbana, M, Jones, PW. [1991]. JPEG DCT algorithm, Digital Compression Techniques, Vol TT7:113-128, SPIE Optical Engineering Press, Bellingham, WA.