Ordered process:
1. dilation - thicken white portion of subtitles
2. resize - temporary hardcoded to 47% (assuming subtitles are 68 pixels in height)
3. apply hsv color mask - filter out non gray pixels and filter out pixels that are not bright enough
4. invert image - make it black text on white background
5. add border to top and bottom - assuming subtitles are cropped closely
