Like I said, it would be much easier if you started with the image with the transparent background.
Just open it in an image editor that supports transparency (pretty much anything besides MS PAINT), select one cell, crop, save.
I used GIMP. Opened the image you posted, erased the background. Then captured (eyedropper) the dark blue color near the edge of the image, selected the whole image to prevent drawing in the background, and gradually shaded the edges to get a matching blueish color (or get rid of the yellow from the background). Then I did the same with the red areas. As you can see, it didn't turn out perfect, and would take a bunch more time.
Which image editor are you using? Can you post the original character set with the transparency?