This function returns a vector of the vertical locations of the areas between the text lines of each sentence in the text.
1. text_lines = vector of vertical locations of sentences
2. text_height = height of each sentence (thickness of the sentence)
Assume that the text image is pre-processed so the text is correctly aligned. Also, the image should have values of 1 or 0. If not, the function may not ouput the correct result.