def pass_bytesize(color_mode, depth, width, height)
      return 0 if width == 0 || height == 0
      (scanline_bytesize(color_mode, depth, width) + 1) * height
    end
def pass_bytesize(color_mode, depth, width, height)
      return 0 if width == 0 || height == 0
      (scanline_bytesize(color_mode, depth, width) + 1) * height
    end
Returns the number of bytes used for an image pass
 @param [Integer] color_mode The color mode in which the pixels are
   stored.
 @param [Integer] depth The color depth of the pixels.
 @param [Integer] width The width of the image pass.
 @param [Integer] height The height of the image pass.
 @return [Integer] The number of bytes used per scanline in a datastream.