Python Pillow和JPEG文件的奇怪问题-像素元组元素不断减少。为什么？

Question

我有一个(非常)的隐写术python程序的草稿，它在图片中对秘密信息进行编码。现在，我只是简单地根据消息的下一个二进制元素(消息转换为ascii十六进制，然后是二进制)，将每个3000个像素的第三个元素调高或调低一个。

我的问题有些离题，但我包含了我的所有代码，所以如果有人真的想表现得很好，他们可以简单地复制和复制代码(也许必须通过pip安装pillow，获取图像，并为myascii模块创建一个单独的python脚本，但仅此而已)。

我的问题是:每次运行这段代码时，print(pxwidth-1，height-1)和print(pxwidth-2，height-2)在每个RGB值中都会递减1。我不明白为什么要救我的命。因此，一些终端输出如下所示：

PS C:\Users\xxx> & C:/Users/xxx/AppData/Local/Programs/Python/Python38-32/python.exe c:/Users/xxx/Desktop/Python_stuff/assorted/steganography/steganography.py
['4B', '65', '6C', '6C', '65', '79', '27', '73', '20', '66', '61', '76', '6F', '72', '69', '74', '65', '20', '63', '6F', '6C', '6F', '72', '20', '69', '73', '20', '67', '72', '65', '65', '6E', '2E']
010010110110010101101100011011000110010101111001001001110111001100100000011001100110000101110110011011110111001001101001011101000110010100100000011000110110111101101100011011110111001000100000011010010111001100100000011001110111001001100101011001010110111000101110
(75, 51, 17)
(74, 50, 16)
(73, 37, 13)
PS C:\Users\xxx> & C:/Users/xxx/AppData/Local/Programs/Python/Python38-32/python.exe c:/Users/xxx/Desktop/Python_stuff/assorted/steganography/steganography.py
['4B', '65', '6C', '6C', '65', '79', '27', '73', '20', '66', '61', '76', '6F', '72', '69', '74', '65', '20', '63', '6F', '6C', '6F', '72', '20', '69', '73', '20', '67', '72', '65', '65', '6E', '2E']
010010110110010101101100011011000110010101111001001001110111001100100000011001100110000101110110011011110111001001101001011101000110010100100000011000110110111101101100011011110111001000100000011010010111001100100000011001110111001001100101011001010110111000101110
(74, 50, 16)
(73, 49, 15)
(73, 37, 13)
PS C:\Users\xxx> & C:/Users/xxx/AppData/Local/Programs/Python/Python38-32/python.exe c:/Users/xxx/Desktop/Python_stuff/assorted/steganography/steganography.py
['4B', '65', '6C', '6C', '65', '79', '27', '73', '20', '66', '61', '76', '6F', '72', '69', '74', '65', '20', '63', '6F', '6C', '6F', '72', '20', '69', '73', '20', '67', '72', '65', '65', '6E', '2E']
010010110110010101101100011011000110010101111001001001110111001100100000011001100110000101110110011011110111001001101001011101000110010100100000011000110110111101101100011011110111001000100000011010010111001100100000011001110111001001100101011001010110111000101110
(73, 49, 15)
(72, 48, 14)
(73, 37, 13)

程序和模块如下：

#def encode(myimage):


#def decode(myimage):

import bin_hex_ascii_converter as myascii

myascii.hex_to_dec("34")
#letter_to_ascii_hex(letter):
#hex_to_bin(foo):
from PIL import Image
foo = Image.open("C:/Users/xxx/Pictures/Saved Pictures/funny_image_encoded.jpg")
#foo = Image.open("C:/Users/xxx/Pictures/Saved Pictures/funny_image.jpg")
#myImage.show()

secret_message = "Jimmie's favorite color is green."

msg = []
for let in secret_message:
   msg.append(myascii.letter_to_ascii_hex(let))
print(msg)

msg_bin = ""
for myhex in msg:
   msg_bin += myascii.hex_to_bin(myhex)
print(msg_bin)

px = foo.load()

width = foo.size[0]
height = foo.size[1]

print(px[width-1,height-1])
print(px[width-2,height-2])

secret_separation = 3000
bar = 0
myiter = 0
limit = len(msg_bin)
for i in range(0,height):
   for j in range(0,width):
       if bar % 3000 == 0 and myiter < limit:
           temp = int(msg_bin[myiter])
           if temp == 0:
               temp = -1
           px[j,i] = (px[j,i][0], px[j,i][1], px[j,i][2]+temp)
           myiter += 1
       bar += 1

#px[5,5] = (px[5,5][0], px[5,5][1], px[5,5][2]+1)
foo.save("C:/Users/xxx/Pictures/Saved Pictures/funny_image_encoded.jpg","JPEG")
print(px[5,5])

另外，我作为myascii导入的模块是：

#hex to dec conversion
def hex_to_dec(foo):
    letts = " ABCDEF"
    if foo[0] in letts:
        num1 = 9 + letts.index(foo[0])
    else:
        num1 = int(foo[0])
    if foo[1] in letts:
        num0 = 9 + letts.index(foo[1])
    else:
        num0 = int(foo[1])
    return num1*16 + num0

def ascii_to_letter(foo):
    low_lett = "abcdefghijklmnopqrstuvwxyz"
    upp_lett = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    #ADD comma and period as well
    if foo == 44:
        return ","
    if foo == 46:
        return "."
    if foo == 32:
        return " "
    if foo == 63:
        return "?"
    if foo > 96 and foo < 123:
        return low_lett[foo - 97]
    if foo > 64 and foo < 91:
        return upp_lett[foo - 65]
    #otherwise
    return "*"

def letter_to_ascii_hex(letter):
    return hex(ord(letter))[2:].upper()

# Returning one byte (8 bits)
def hex_to_bin(foo):
    myarr = ["0000",
    "0001",
    "0010",
    "0011",
    "0100",
    "0101",
    "0110",
    "0111",
    "1000",
    "1001",
    "1010",
    "1011",
    "1100",
    "1101",
    "1110",
    "1111"]

    num2 = foo[0]
    if num2 == "A":
        num2 = "1010"
    elif num2 == "B":
        num2 = "1011"
    elif num2 == "C":
        num2 = "1100"
    elif num2 == "D":
        num2 = "1101"
    elif num2 == "E":
        num2 = "1110"
    elif num2 == "F":
        num2 = "1111"
    else:
        num2 = myarr[int(num2)]

    num1 = foo[1]
    if num1 == "A":
        num1 = "1010"
    elif num1 == "B":
        num1 = "1011"
    elif num1 == "C":
        num1 = "1100"
    elif num1 == "D":
        num1 = "1101"
    elif num1 == "E":
        num1 = "1110"
    elif num1 == "F":
        num1 = "1111"
    else:
        num1 = myarr[int(num1)]

    return num2 + num1

另外，我使用的图片是：https://www.bing.com/images/search?view=detailV2&ccid=FOFci7yV&id=AA468BC3FE90B8D67D34C7884C3578A69D815E52&thid=OIP.FOFci7yV8pJTXQxPI9OYpgHaHk&mediaurl=https%3A%2F%2Fwww.laughtard.com%2Fwp-content%2Fuploads%2F2019%2F02%2F50-Funny-Animal-Pictures-That-You-Need-In-Your-Life-37.jpg&exph=1000&expw=979&q=funny+images&simid=608028465397174105&ck=A56AB62FC7B4F29A99A099EF131B8CDB&selectedindex=0&ajaxhist=0&first=1&scenario=ImageBasicHover&vt=0&sim=11

Answer 1

正如马克·兰瑟姆指出的那样--jpeg是有损的文件格式。改用png解决了这个问题。