Ditto - John, I feel the same way. Thanks, Lee, I am just delving into compressions, because my disk image from a DVD had this new to me extension cdr , and on Apple discussions I found out this is a Master disk with less compression than usual. So I will be learning about compression in files etc which I had not even thought of before. I suppose one way is to use Webopedia and ask for the meaning of JPEG, TIFF and all the rest, or maybe I should google under Compression. Marta................................................................... ......... He that is the author of a war lets loose the whole contagion of hell and opens a vein that bleeds a nation to death. -Thomas Paine, philosopher and writer (1737-1809) On Mar 28, 2005, at 11:00, John Robinson wrote:
> Lee, > > Thanks, as usual for a great explanation, but just for your info. my > eyes glaze over on most anything you say as you speak so far above my > capabilities, but boy do I ever learn from you!! > > John R. > > > > > On Mar 28, 2005, at 10:54 AM, Lee Larson wrote: > >> On Mar 27, 2005, at 9:22 PM, Bill King puzzled: >> >>> I just read an interesting article posted on MacSurfer from the >>> Syracuse Post-Standard newspaper. It concerned the ability of >>> iPhoto 5 to repetitively save a picture using JPG compression and >>> apparently losslessly. >>> >>> I would love to hear for any graphics compression experts about the >>> authenticity of this technique... >> >> I'm not a graphics expert, but I think I can explain what's going on. >> >> The JPEG scheme is actually a whole collection of different >> compression techniques all lumped into one standard. The most common >> one chosen is what's called "discrete cosine transform" (DCT) >> compression. Within the DCT algorithm, you can choose the amount of >> information to be retained. (It's just the value of a constant in the >> formula.) The more information that's retained, the larger is the >> size of the compressed file. It's possible to choose lossless DCT >> compression, at the expense of almost no compression for complicated >> images. >> >> You can see this in programs like Canvas, which has a slider control >> to select the quality of the output image. Sliding it over to 100% >> results in a big file with no quality loss. >> >> The JPEG scheme also includes a lossless algorithm called entropy >> encoding which I believe is less often used than the DCT. >> >> I don't know which scheme Apple uses, but It's probably one of those >> two. >> >> As a postscript to this, let me note that I've had disagreements with >> so-called experts about this. They claimed that JPEG is an inherently >> lossy format while I countered that it need not be. Most "experts" >> don't really understand the capabilities of JPEG because most >> programs don't take advantage of JPEG's real capabilities. I bring up >> the DCT and their eyes glaze over. > > > > | The next meeting of the Louisville Computer Society will > | be March 22. The LCS Web page is <http://www.kymac.org>. > | List posting address: <mailto:macgroup at erdos.math.louisville.edu> > | List Web page: <http://erdos.math.louisville.edu/macgroup> -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: text/enriched Size: 3141 bytes Desc: not available Url : http://www.math.louisville.edu/pipermail/macgroup/attachments/20050328/8ce677d0/attachment.bin
