def to_column_format(self, high_density_vertical=True):
im = self._im.transpose(Image.ROTATE_270).transpose(Image.FLIP_LEFT_RIGHT)<EOL>line_height = <NUM_LIT> if high_density_vertical else <NUM_LIT:8><EOL>width_pixels, height_pixels = im.size<EOL>top = <NUM_LIT:0><EOL>left = <NUM_LIT:0><EOL>while left < width_pixels:<EOL><INDENT>box = (left, top, left + line_height, top + height_pixels)<EOL>im_slice = im.transform((line_height, height_pixels), Image.EXTENT, box)<EOL>im_bytes = im_slice.tobytes()<EOL>yield(im_bytes)<EOL>left += line_height<EOL><DEDENT>
Extract slices of an image as equal-sized blobs of column-format data.

:param high_density_vertical: Printed line height in dots