[magick-users] convert -crop image quality question

[J. Young]

Hi all,

I have some two-page landscape-orientation jpg scans of a book that I 
wish to cut in two to view better on my psp device.

I issued this command to perform the work:

convert bigpage.jpg -crop 50%x0+0+0 page1.jpg
convert bigpage.jpg -gravity East -crop 50%x0+0+0 page2.jpg

So this works ok, but is it a lossless operation as far as image 
quality?  If not, could someone recommend a lossless equivalent?

Thanks so much!