On Fri, 26 Apr 2002 05:02:25 -0500, Samuel W. Heywood wrote: > On Fri, 26 Apr 2002 03:29:35 -0400, Clarence Verge wrote:
> <snip> >> Tell him to zip the .BMPs and rename them to .ZBM. > I have heard some stories about a phenomena called > "lossy compression" According to these stories it is OK to zip > images in some formats, but not others. Among those formats that > are supposedly OK to zip are the BMPs. If you zip a JPG and then > unzip it, the resolution will not be as keen as seen in the original > before it was zipped. Regardless of the format of the source, zipping is ALWAYS 100% lossless. If you zip a JPG you will get exactly the same crappy JPG you had before when you unzip it. Lossy compression exists and is most frequently seen as .JPGs. i.e. the compression method used to produce the .jpg is inherently lossy, and I understand you can trade the amount of compressed size you get against the amount of loss. I have NEVER seen a .JPG without visually noticeably artifacts, so I assume there is no lossless form. > 1. If there is such a thing as "lossy compression", could it be > mimimized by using ARJ, ARC, DWC, LHA, TAR, or some other alternative > to PKZIP? No. Garbage in = garbage out. > 2. Of the many image formats that we know of, and if it is true that > so called "lossy compression" is a problem in the case of some image > formats, which types should not be zipped? Doesn't matter. GIGO. > It could be that all this talk I have heard about "lossy compression" > is just a bunch of bull, but I tell you that a lot of people believe > it. I won't believe it unless I can find an authoritative source on > the subject which confirms the existence of the reported phenomena. > The truth is out there. Does anyone know the URL? http://bedlam.rutgers.edu/x-files/ - Clarence Verge. -- Using Arachne 1.66 on DSL.
