James, caseB was lossy compressed. It is 10% smaller when compressed (gzip, bzip2), so it contains significantly less information.
cheers, Hans James Holton schreef: > Ian Tickle wrote: >> I found an old e-mail from James Holton where he suggested lossy >> compression for diffraction images (as long as it didn't change the >> F's significantly!) - I'm not sure whether anything came of that! >> > > Well, yes, something did come of this.... But I don't think Gerard > Bricogne is going to like it. > > Details are here: > http://bl831.als.lbl.gov/~jamesh/lossy_compression/ > > Short version is that I found a way to compress a test lysozyme dataset > by a factor of ~33 with no apparent ill effects on the data. In fact, > anomalous differences were completely unaffected, and Rfree dropped from > 0.287 for the original data to 0.275 when refined against Fs from the > compressed images. This is no doubt a fluke of the excess noise added > by compression, but I think it highlights how the errors in > crystallography are dominated by the inadequacies of the electron > density models we use, and not the quality of our data. > > The page above lists two data sets: "A" and "B", and I am interested to > know if and how anyone can "tell" which one of these data sets was > compressed. The first image of each data set can be found here: > http://bl831.als.lbl.gov/~jamesh/lossy_compression/firstimage.tar.bz2 > > -James Holton > MAD Scientist >
