[magick-users] convert -crop image quality question

[J. Young]

Gabe Schaffer wrote:
> On 11/6/06, J. Young <jyoung82 at carolina.rr.com> wrote:
>> Gabe Schaffer wrote:
>> > On 11/5/06, Anthony Thyssen <anthony at griffith.edu.au> wrote:
>> >> "J. Young" on  wrote...
>> >
>> >> | 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?
>> >> |
>> >> JPEG to JPEG is always lossless in IM.
>> >
>> > Always lossless? Did you mean never?
>
> That's strange. Did you check out 
> http://www.jpegclub.org/droppatch.tar.gz ??
>
> GNS
>
Ok, I can confirm that the 'jpegtran' from your link does work with 
lossless crop.
Used:
jpegtran -outfile page1.jpg -crop ${halfxres}x${yres}+0+0 bigpage.jpg
jpegtran -outfile page2.jpg -crop ${halfxres}x${yres}+${halfxres}+0 
bigpage.jpg

Thanks for the help.