\[ \begin{align}\begin{aligned}\newcommand\blank{~\underline{\hspace{1.2cm}}~}\\% Bold symbols (vectors) \newcommand\bs[1]{\mathbf{#1}}\\% Differential \newcommand\dd[2][]{\mathrm{d}^{#1}{#2}} % use as \dd, \dd{x}, or \dd[2]{x}\\% Poor man's siunitx \newcommand\unit[1]{\mathrm{#1}} \newcommand\num[1]{#1} \newcommand\qty[2]{#1~\unit{#2}}\\\newcommand\per{/} \newcommand\squared{{}^2} \newcommand\cubed{{}^3} % % Scale \newcommand\milli{\unit{m}} \newcommand\centi{\unit{c}} \newcommand\kilo{\unit{k}} \newcommand\mega{\unit{M}} % % Percent \newcommand\percent{\unit{\%}} % % Angle \newcommand\radian{\unit{rad}} \newcommand\degree{\unit{{}^\circ}} % % Time \newcommand\second{\unit{s}} \newcommand\s{\second} \newcommand\minute{\unit{min}} \newcommand\hour{\unit{h}} % % Distance \newcommand\meter{\unit{m}} \newcommand\m{\meter} \newcommand\inch{\unit{in}} \newcommand\foot{\unit{ft}} % % Force \newcommand\newton{\unit{N}} \newcommand\kip{\unit{kip}} % kilopound in "freedom" units - edit made by Sri % % Mass \newcommand\gram{\unit{g}} \newcommand\g{\gram} \newcommand\kilogram{\unit{kg}} \newcommand\kg{\kilogram} \newcommand\grain{\unit{grain}} \newcommand\ounce{\unit{oz}} % % Temperature \newcommand\kelvin{\unit{K}} \newcommand\K{\kelvin} \newcommand\celsius{\unit{{}^\circ C}} \newcommand\C{\celsius} \newcommand\fahrenheit{\unit{{}^\circ F}} \newcommand\F{\fahrenheit} % % Area \newcommand\sqft{\unit{sq\,\foot}} % square foot % % Volume \newcommand\liter{\unit{L}} \newcommand\gallon{\unit{gal}} % % Frequency \newcommand\hertz{\unit{Hz}} \newcommand\rpm{\unit{rpm}} % % Voltage \newcommand\volt{\unit{V}} \newcommand\V{\volt} \newcommand\millivolt{\milli\volt} \newcommand\mV{\milli\volt} \newcommand\kilovolt{\kilo\volt} \newcommand\kV{\kilo\volt} % % Current \newcommand\ampere{\unit{A}} \newcommand\A{\ampere} \newcommand\milliampereA{\milli\ampere} \newcommand\mA{\milli\ampere} \newcommand\kiloampereA{\kilo\ampere} \newcommand\kA{\kilo\ampere} % % Resistance \newcommand\ohm{\Omega} \newcommand\milliohm{\milli\ohm} \newcommand\kiloohm{\kilo\ohm} % correct SI spelling \newcommand\kilohm{\kilo\ohm} % "American" spelling used in siunitx \newcommand\megaohm{\mega\ohm} % correct SI spelling \newcommand\megohm{\mega\ohm} % "American" spelling used in siunitx % % Inductance \newcommand\henry{\unit{H}} \newcommand\H{\henry} \newcommand\millihenry{\milli\henry} \newcommand\mH{\milli\henry} % % Power \newcommand\watt{\unit{W}} \newcommand\W{\watt} \newcommand\milliwatt{\milli\watt} \newcommand\mW{\milli\watt} \newcommand\kilowatt{\kilo\watt} \newcommand\kW{\kilo\watt} % % Energy \newcommand\joule{\unit{J}} \newcommand\J{\joule} % % Composite units % % Torque \newcommand\ozin{\unit{\ounce}\,\unit{in}} \newcommand\newtonmeter{\unit{\newton\,\meter}} % % Pressure \newcommand\psf{\unit{psf}} % pounds per square foot \newcommand\pcf{\unit{pcf}} % pounds per cubic foot \newcommand\pascal{\unit{Pa}} \newcommand\Pa{\pascal} \newcommand\ksi{\unit{ksi}} % kilopound per square inch \newcommand\bar{\unit{bar}} \end{aligned}\end{align} \]

Feb 17, 2025 | 550 words | 6 min read

12.2.3. Task 3

Learning Objectives

Encode a binary message into an image by altering the least significant bits of the pixel values.

Task Instructions

Save the flowcharts for each of your tasks in tp2_team_3_teamnumber.pdf You will also need to include these flowcharts in your final report.

Create a function that takes the binary message, an input image file path, and an output image file path as its only arguments. This function should first load the input image and check if the binary message can fit into it. If the binary message is too long to be encoded into the image, the function should print an error message. Otherwise, the function should encode the binary message into the image by altering the least significant bits of the pixel values. Start in the upper left corner of the image, and proceed left to right across each row. For color images, iterate over each channel (R, G, B) of each pixel before moving to the next pixel. Write the modified image to the output file path.

Finally, create a main function in your Python program that builds on the code you developed in Task 2 and uses the function described above to encode a message into an image. Your main function should prompt the user to enter a plaintext message, a key, a start sequence, an end sequence, a path to an image file, and a path to an output file. It should then encrypt the message using the Beaufort cipher, generate the binary message, encode the binary message into the image, and save the modified image to the output file. Finally, it should display a message indicating whether the message has been successfully encoded into the image and saved to the specified path. Use the files provided in the Table 12.37 to test your code.

Note

The matplotlib module converts grayscale images to color images when they are saved using imsave. So you will need to use the PIL library to when saving your output images. You can use the save method of the Image class to save the image to a file. Here is an example of how you can save a grayscale image using the PIL library:

from PIL import Image
pil_image = Image.fromarray(img_array, mode="L")
pil_image.save(img_path)

For color images, set the mode argument to RGB.

See the PIL documentation for more information.

Save your program as tp2_team_3_teamnumber.py.

Notes

• The encoded image should appear visually identical to the original image, as changes to the LSBs are typically imperceptible to the human eye.

• The encoded message will not be visible when viewing the image, but it can be extracted programmatically by decoding the LSBs.

• The program should handle both grayscale and color images effectively, ensuring that the image data is properly prepared for encoding.

Table 12.37 Image Files

Image File Name	Description
ref_gry.png	Original grayscale image
ref_gry_b.png	Grayscale image with Beaufort encrypted message encoded
ref_col.png	Original color image
ref_col_b.png	Color mage with Beaufort encrypted message encoded

Sample Output

Use the values in Table 12.38 below to test your program.

Table 12.38 Test Cases

Case	plaintext	Beaufort key	start_seq	end_seq	input image path	output image path
1	hello	Secret	007	700	ref_col.png	ref_col_b.png
2	World	ENGR133	007	700	ref_gry.png	ref_gry_b.png
3	Hello World	Mystery	007	700	ref_gry.png	error.png

Ensure your program’s output matches the provided samples exactly. This includes all characters, white space, and punctuation. In the samples, user input is highlighted like this for clarity, but your program should not highlight user input in this way.

Case 1 Sample Output

$ python3 tp2_team_3_teamnumber.py Enter the plaintext message you want to encrypt: hello Enter the key for Beaufort cipher: Secret Enter the start sequence: 007 Enter the end sequence: 700 Enter the path of the image: ref_col.png Enter the path for the encoded image: ref_col_b.png Encrypted Message using Beaufort Cipher: la1g0 Binary output message: 0011000000110000001101110110110001100001001100010110011100110000001101110011000000110000 Message successfully encoded and saved to: ref_col_b.png

Fig. 12.4 Case_1_ref_col_b.png

Case 2 Sample Output

$ python3 tp2_team_3_teamnumber.py Enter the plaintext message you want to encrypt: World Enter the key for Beaufort cipher: ENGR133 Enter the start sequence: 007 Enter the end sequence: 700 Enter the path of the image: ref_gry.png Enter the path for the encoded image: ref_gry_b.png Encrypted Message using Beaufort Cipher: s9zgy Binary output message: 0011000000110000001101110111001100111001011110100110011101111001001101110011000000110000 Message successfully encoded and saved to: ref_gry_b.png

Fig. 12.5 Case_2_ref_gry_b.png

Case 3 Sample Output

$ python3 tp2_team_3_teamnumber.py Enter the plaintext message you want to encrypt: Hello World Enter the key for Beaufort cipher: Mystery Enter the start sequence: 007 Enter the end sequence: 700 Enter the path of the image: ref_gry.png Enter the path for the encoded image: error.png Given message is too long to be encoded in the image. Encrypted Message using Beaufort Cipher: fuhi0 c8hhq Binary output message: 0011000000110000001101110110011001110101011010000110100100110000001000000110001100111000011010000110100001110001001101110011000000110000

Table 12.39 Deliverables

Deliverables	Description
tp2_team_3_teamnumber.py	Your completed Python code.
tp2_team_3_teamnumber.pdf	Flowchart(s) for this task.