This happens because the information is de-compressed. JPEG images are compressed, and information is lost in creating them because of the lossy compression. During de-compression no information gets lost further, it just gets inflated back to the original file size. PSD has some compression, and also TIF has this option, but is using a lossless compression, like using ZIP as a compression. The new JPEG2 format (extension is jp2) is supposed to be better, and even allows for lossless compression. However when using lossless compression the jp2 files are quite big as well, but still smaller then uncompressed formats.
On Sat, 2003-12-06 at 22:49, Shel Belinkoff wrote: > Hi gang, > > When converting a JPEG file to PSD format, the size grows considerably. > For example, a 1.5mb file from my digicam becomes almost 10mb in size. > I don't object to that, but was just wondering about the mechanics of > how that happens within PS. > Anybody know? Is it interpolated upwards, or perhaps the information is > already somewhere in the JPEG file? I believe it also happens when > converting a JPEG to a TIFF. Is that done in the same manner as the > conversion to PSD? > > Now, the real question is this: is any information lost or created in > such conversions that it degrades the image making it better to shoot in > TIFF format, or is the image information only improved and not harmed in > any way by making the change? > > shel -- Frits W�thrich <[EMAIL PROTECTED]>
