Can I segment characters from this image with CSV?
Your results (above) looks well for character segmentation. But if you have some problems with calculation of thresholds for total image, you can try slightly different approach. "Column sum vector" method works well for grey images too, but not only for black/white images. So there is no need to calculate threshold for total image, but you must choose some value for segmentation in vector. May be it will slightly simpler to do segmentation in this case.

You can use "line sum vector" for vertical segmentation   too.