line text image segmentation

Suppose I have the following image

I want to surround the white text appears within the black background with black pixels so that there will be boundaries at the (top,bottom,left and right). the result will be as follows

for clarification: I used the following image:

as you see at the left I want to add a black pixels so that the letter "I" will be separated from the white background. The same process should be applied to right and the bottom which related to "Y" letter. Also at the top the letter "A"and "I" should be separated by black pixels from the top white background. The result of this image should be as follows: