Imagemagick convert with resample option
- by coneybeare
I am creating thumbnails from much larger images and have been using this command successfully for some time:
convert FILE -resize "64x" -crop "64x64+0+16" +repage -strip OUTFILE
I also do some other processing that is not relevant to the question. I realized that this does not adjust the resolution at all, so if I use a 300dpi image, it ends up displaying really small on some devices. I want to resample it to 72x72 so I have been trying with this command:
convert FILE -resize "64x" -crop "64x64+0+16" +repage -strip -resample 72x72 OUTFILE
And expected the 64x64 image at 300dpi to be resampled to a 64x64 image at 72dpi, but instead, I am getting a very funny size and density.
Here is "identify" output for the original and post-processed file WITHOUT the resample:
coneybeare $ convert "aa.jpg" -crop "64x64+0+16" +repage -strip "aa.png"
coneybeare $ for image in `find . -type f`; do identify $image; identify -verbose $image | egrep "^ Resolution"; done
./aa.jpg JPEG 1130x1695 1130x1695+0+0 8-bit DirectClass 1.492MiB 0.000u 0:00.000
Resolution: 300x300
./aa.png PNG 64x64 64x64+0+0 8-bit DirectClass 7.46KiB 0.000u 0:00.000
Resolution: 118.11x118.11
And here is the "identify output for the command WITH the resample:
coneybeare $ convert "aa.jpg" -crop "64x64+0+16" +repage -strip -resample 72x72 "aa.png"
coneybeare $ for image in `find . -type f`; do identify $image; identify -verbose $image | egrep "^ Resolution"; done
./aa.jpg JPEG 1130x1695 1130x1695+0+0 8-bit DirectClass 1.492MiB 0.000u 0:00.000
Resolution: 300x300
./aa.png PNG 15x15 15x15+0+0 8-bit DirectClass 901b 0.000u 0:00.000
Resolution: 28.34x28.34
So, the question is: What am I doing wrong and how can I fix it so the end result is a 64x64 cropped thumbnail image at 72dpi?
