What paint program are you using? I'm not sure about the others, but Photoshop has a great selection tool called the magic wand. If it were me, I'd click on the black background area outside your transmap with the magic wand selection tool. Then convert that to green or some other unique color. Then use the magic wand again, this time usig the select by color feature and select all of the black in the picture.. in this case since everything outside your transmap is now green all that is left should be the black spaces inside your figure. Once you have them selected, fill with white. Once that is accomplished I'd then select the green area and convert it back to black.