On Sun, Nov 6, 2011 at 11:23 AM, Heiko Schulz <aeitsch...@yahoo.de> wrote: >>If your using dxt compression, which is why most people use dds, then >>it is NOT equal to the original image. Amount of degradation will >>depend on the image, resolution, type of dxt used, etc..but will never >>be the same or better quality. > > This applies to every texture file which use compression. So it belongs to > .png, .rgb and .jpg as well. I never heard that anyone asked for the source > here.... > There is always a degradation, the question is, is it visible to human eyes?
Well, not quite-- PNG and SGI/RGB use non-lossy algorithms for compression-- when uncompressed you get back exactly what you put in. They don't degrade the data, so archiving in these formats is fine. Formats like JPG and DDS/DXT use the source data to generate a compressed version, but the new version can't be restored to the exact original data. (Try a comparison between original and compressed versions examined on the pixel level-- it's interesting and revealing.) This means these are not good formats for archiving source material that might be edited later. With lossy formats using high-quality, low-compression settings, you might not visually notice degradation on the first edit, but you will eventually see substantial differences on subsequent edits. Each time you edit from an new lossy-compression source, you lose information, but you do not with the algorithms used by PNG and SGI/RGB. On a personal note, I had a lot of trouble getting co-workers to stop archiving their source images as JPG files. It took a lot of explaining and re-explaining. ;) -Gary ------------------------------------------------------------------------------ RSA(R) Conference 2012 Save $700 by Nov 18 Register now http://p.sf.net/sfu/rsa-sfdev2dev1 _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
