Table 3. Image processing functions

	Function
d_read	Reads data from CSV file recording signal strength.
d_gradation	Gradation (and color) is assigned for between the maximum and the minimums of a received signal at 8 bits.
_draw	Draws an image page consisting of 40 columns and n lines.
_combine	Combines multiple pages into a single Picture.
p_save	Saves image in TIFF format.