returns a float number, which tells the quality of the output image
the number is the average number of bits used per one byte (each pixel = 4 bytes). Only bytes from pixels which are used to hold
data are considered in the calcualtion, untouched pixels are not counted as they remain as-they-were;
the number can be at max 8 (saturated image), lowest 0 (no data & highest quality). Lower means higher quality.
returns a float number, which tells the quality of the output image
the number is the average number of bits used per one byte (each pixel = 4 bytes). Only bytes from pixels which are used to hold data are considered in the calcualtion, untouched pixels are not counted as they remain as-they-were; the number can be at max 8 (saturated image), lowest 0 (no data & highest quality). Lower means higher quality.