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
