I have a 4000x3000, 3.7MB JPEG2000 file that I'm trying to process into cropped tiles. I do this with a command like:

```
convert 486.jp2 -crop 256x256+0+0 -format jpg 486_crop.jpg

```

This command takes 5 seconds to run on a current-model Mac Pro. ImageMagick is using the Jasper library, which I've read is very slow. I just want to make sure I'm not botching the command somehow before I abandon ImageMagick in this application.