python - OpenCV - Disable all pixel alteration when saving as JPEG -


i'm writing utility least significant bit (lsb) steganography in python (2 , 3 compatability) opencv-python package (opencv-python==3.2.0.8). seems work flawlessly numerous png files i've tested, i've noticed that, seemingly no matter what, jpeg files have pixels altered every time call cv2.imwrite. here's save method lsbcodec class:

class lsbcodec(object):     # ...      def save(self, filename):         ext = filename.split(".")[-1].lower()  # assumptions made          if ext in ("jpg", "jpeg", "jpe"):             args = [[int(cv2.imwrite_jpeg_quality), 100]]         elif ext in ("png",):             args = [[int(cv2.imwrite_png_compression), 0]]         else:             args = []         cv2.imwrite(filename, self.img, *args)

however, still alters pixels. altering them 1 bit throws off entire program (since least significant bits used data , metadata storage).

for example, first 3 bits should either 0's or 1's , determine if simple xor key should provided decoding data. second 3 bits determine number of least significant bits use following data. using 2 bits , no xor key, value encoded should 0b000010 (but stored reversed) spread out on first 2 pixels (6 channels).

original first 2 pixels:
[ 44 120 216], [ 43 119 215] last bits: 000111

encoded first 2 pixels:
[ 44 121 216], [ 42 118 214] last bits: 010000 (reversed)

stored first 2 pixels:
[ 44 121 217], [ 42 118 214] should same above

how can save jpeg file without altering pixels in way? or not feasible because of jpeg image codec unfamiliar? work if changed extension png?


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