Well, I'm very happy. I just figured out how to crop what I want from the jp2 using OpenEV.
Begin the program.
Go to File - OpenBegin the program.
Go to File - Open - and open your huge jp2 file.
After a few minutes the jp2 image will appear in the program.
Now, click on File - Export.
Press the Advanced Options button.
Now go back to the top left of the export screen and click the Output button. (Do not try to fill in the blank on the screen beside output - it won't register correctly and will fool you).
When you click the output button, you get a new box. Just fill in the name that you want to call your output file; i.e. c:\marsrocks\ev crop test
Once you have named the file you are creating, click okay. (The file you named will now appear beside the output button on the export screen).
Under your basics options box, select your output format. Choose jpeg, bmp, or whatever you want the new file to be from the list.
Make sure you select "Full" in the box beside output resolution. If you want less than a 1:1 image, then select the one you want.
Now go down to the interactive options box.
Make sure that you press the button that says "Window input file" (if you don't make sure that the "window input file" button is pressed down, the program will spend an hour trying to convert the whole image instead of just the part of the image that you crop).
Now, in the same interactive options box, click on Draw ROI mode. (ROI means Region of Interest).
Now, switch back to your image view window in the program.
Now, with your mouse, you are going to describe the part of the image you want to crop: Start in the upper left corner of your selected area and click your left mouse button, then drag the mouse diagonally down and to your right and then release the mouse button. This will give you an orange box which is the part of the image that you are cropping. If you missed the area you wanted, just click and drag your mouse again, and it will give you a new box in the new location. Alternatively, hover over one of the orange lines, and then when it darkens, you can drag the line to a new spot.
When trying the above for the first time, draw a very small box. If you made a mistake as I did the first few times, the file you create should be small, and it will hopefully only take a few minutes to try again.
When you are satisfied you have a box around the region of interest you want to select, go back to the Export Tool screen, and click on "Export" in the lower left corner of the box.
The program will now produce the file for you at 1:1 of the section you selected in the image format you selected. This could take a few minutes to an hour depending on how big of an area you picked.
If you picked too big of a section your graphics program may not be able to open it, so watch out.
Once your new file has been created, just pull it up in your normal graphics program, and work with it as any other image.
Raw Images Courtesy of NASA and ESA. Special thanks to EVERYONE who has contributed in the search for Mars anomalies. Also thanks to Google, Picasa, ImageShack, and Photobucket.