Convert to ppm (pnm) image format:

Since the program 'xv' is not available in our unix enivonment anymore, you will
have to use other programs to convert an image to ppm/pnm format. In our cis
unix environment, you can use the program 'gimp' to do the job.

How to convert to ppm/pnm using gimp
 

Find a machine in our lab, type 'gimp'.  If you never use gimp before, you will need to
answer a few questions to install the program.

Go to the main menu, select File -> Open to open your imag.

Now move the mouse to the image window, click the right mouse button, select 'File' -> 'Save as',
and then choose 'PNM' in the 'Save Option' panel. This will allow you to convert and
save the input image to a PNM (ppm) file.

Resize your image

To resize your image (so that you will satisfy the power of 2 requirement in OpenGL),  move
your mouse cursor to the image window, click the right mouse button, choose 'Image' ->
'Scale Image', and then input the desired pixel width and height to resize the image.