Image Class Reference

Defines a dinamically allocated PPM image and provides various methods to manipulate and access the image data. More...

#include <Image.h>

Public Member Functions
	Image ()
	Default constructor for the Image class.
	Image (int w, int h)
	Constructor to initialize an image with given width and height.
int	GetWidth () const
	Gets the Width object.
int	GetHeight () const
	Gets the Height object.
void	AllocatePixels ()
	Memory allocation of the matrix of pixels, which is fundamental in defining any Image object.
void	LiberatePixels ()
	Deallocates the memory previously allocated by the AllocatePixels() function, as well as the memory alocated by the array of the pixels' 'R', 'G' and 'B' values.
void	GetPixels ()
	Function that fills in the matrix of pixels.
bool	ExtensionCheck (const string &input_text, const string &file_type)
	Function that checks if a string ends with the valid substring.
void	PrintPPM () const
	Function that prints out the parameters of a PPM image. Mostly used for testing purposes.
string	CreatePPM () const
	Function that creates a string containing all the data of a PPM image.
bool	ReadPPM (const string &file_name)
	Reads and dynamically stores the content of an image from a valid PPM file.
void	ShowArray () const
	Function that outputs a previously defined array of 'R', 'G' and 'B' values. Mostly used for testing purposes.
string	IntToBin (int num, int bits=8)
	Function that receives an integer value and converts it to binary.
void	CodeMsg (string msg)
	Main function used in encrypting and hiding an ASCII message inside the least significant bits (LSB) of a PPM image's pixels.
int	BinToInt (string bin_num, int index=0)
	Recursive function used to convert a binary value into an integer value.
void	DecodeMsg ()
	Main function used in uncovering and decrypting an ASCII message inside the least significant bits (LSB) of a PPM image's pixels.

Detailed Description

Defines a dinamically allocated PPM image and provides various methods to manipulate and access the image data.

Constructor & Destructor Documentation

Image() [1/2]

Image::Image ( )

inline

Default constructor for the Image class.

: width(0), height(0), pixel(nullptr), pixel_array(nullptr) {}

Image() [2/2]

Image::Image ( int w, int h )

inline

Constructor to initialize an image with given width and height.

< This variable defines the size of the array of pixels, counting each R, G and B value as a separate unit of the array.

                        : width(w), height(h)
    {
        size = (width * height) * 3; 
    }

Member Function Documentation

AllocatePixels()

void Image::AllocatePixels ( )

inline

Memory allocation of the matrix of pixels, which is fundamental in defining any Image object.

    {
        pixel = new Pixel *[height];
        for (int i = 0; i < height; i++)
        {
            pixel[i] = new Pixel[width];
        }
    }

BinToInt()

int Image::BinToInt ( string bin_num, int index = 0 )

inline

Recursive function used to convert a binary value into an integer value.

Parameters

bin_num	String containing the binary value that will be converted into an integer.
index	The index of the string.

Returns

the sum of the current and subsequent values acquired recursively.

Base case: if the index reaches the end of the binary string.

Recursive call to calculate the value of the current and subsequent binary digits.

    {
        if (index == bin_num.length())
        {
            return 0;
        }
 
        int value_current = (bin_num[index] - '0') * pow(2, bin_num.length() - 1 - index);
        int value_subsequent = BinToInt(bin_num, index + 1);
 
        return value_current + value_subsequent;
    }

CodeMsg()

void Image::CodeMsg ( string msg )

inline

Main function used in encrypting and hiding an ASCII message inside the least significant bits (LSB) of a PPM image's pixels.

Parameters

msg	Message that will be stored inside the image.

‍The number of characters in the message.

‍Array that stores the ASCII values of each of the message's characters.

Fills in the chars[] array.

Stores the binary value of the number of characters in the message.

Modification of the first 8 bits of the array of 'R', 'G' and 'B' values, which store the message's size.

Modifies the bits of the array of 'R', 'G' and 'B' values which will store the actual message.

‍Index for each of the message's bits.

    {
        int t = msg.size(); 
        int chars[t]; 
        for (int i = 0; i < t; ++i)
        {
            chars[i] = (int)msg[i];
        }
 
        string bin = IntToBin(t);
 
        for (int i = 0; i < 8 && i < size; ++i)
        {
            if (bin[i] == '1')
            {
                if (pixel_array[i] % 2 == 0)
                {
                    pixel_array[i]++;
                }
            }
            else
            {
                if (pixel_array[i] % 2 != 0)
                {
                    pixel_array[i]++;
                }
            }
        }
 
        int bit_index = 0; 
        for (int j = 0; j < t; ++j)
        {
            bin = IntToBin(chars[j]);
            for (int i = 0; i < 8 && (bit_index + 8) < size; ++i, ++bit_index)
            {
                if (bin[i] == '1')
                {
                    if (pixel_array[bit_index + 8] % 2 == 0)
                    {
                        pixel_array[bit_index + 8]++;
                    }
                }
                else
                {
                    if (pixel_array[bit_index + 8] % 2 != 0)
                    {
                        pixel_array[bit_index + 8]++;
                        if (pixel_array[bit_index + 8] == 255)
                        {
                            pixel_array[bit_index + 8]--;
                        }
                    }
                }
            }
        }
    }

CreatePPM()

string Image::CreatePPM ( ) const

inline

Function that creates a string containing all the data of a PPM image.

Returns

all the information needed to define a PPM image.

Gets the pixels from a previously defined array of pixels.

    {
        stringstream img_content;
 
        img_content << "P3" << endl;
        img_content << width << " " << height << endl;
        img_content << max_color << endl;
 
        for (int i = 0; i < size; i += 3)
        {
            img_content << pixel_array[i] << " " << pixel_array[i + 1] << " " << pixel_array[i + 2] << " ";
            if ((i / 3 + 1) % width == 0)
            {
                img_content << endl; 
            }
        }
        return img_content.str();
    }

DecodeMsg()

void Image::DecodeMsg ( )

inline

Main function used in uncovering and decrypting an ASCII message inside the least significant bits (LSB) of a PPM image's pixels.

‍String that stores the size of the message in binary.

Gets (in binary) the size of the message stored in the image from the first 8 bits of it's pixels' 'R', 'G' and 'B' values, previously stored in an array.

Adds the character '0' to bin_size.

Adds the character '1' to bin_size.

‍String that stores the ASCII message in binary.

‍Stores the size of the image as an integer value.

Gets (in binary) the message stored in the image, using the message's size and using the array of the pixels' 'R', 'G' and 'B' values.

Adds the character '0' to bin_msg.

Adds the character '1' to bin_msg.

‍String that stores the completely decoded message.

Repeats the process below until every character of the message has been decoded and stored.

‍Stores a binary value of a single character.

Gets 8 bits (or a single character) from the message in binary, then adds up so it does the same to the next bit (if there is a next bit).

‍Stores the decoded ASCII character as a char.

Pushes a new decoded character into the string that stores the message.

    {
        string bin_size; 
        for (int i = 0; i < 8; ++i)
        {
            if (pixel_array[i] % 2 == 0)
            {
                bin_size.push_back('0'); 
            }
            else
            {
                bin_size.push_back('1'); 
            }
        }
 
        string bin_msg; 
        int msg_size = BinToInt(bin_size); 
        for (int i = 8; i < 8 + (msg_size * 8); ++i)
        {
            if (pixel_array[i] % 2 == 0)
            {
                bin_msg.push_back('0'); 
            }
            else
            {
                bin_msg.push_back('1'); 
            }
        }
 
        string decoded_msg; 
        for(int j = 0; j < msg_size; ++j) 
        {   
            string bin_char; 
            for(int i = 0; i < 8; ++i) 
            {
                bin_char.push_back(bin_msg[i + (8 * j)]);
            }
 
            char single_char = BinToInt(bin_char); 
            decoded_msg.push_back(single_char); 
        }
        cout << "\033[94mA mensagem escondida é: \033[0m" + decoded_msg << "\n";
    }

ExtensionCheck()

bool Image::ExtensionCheck ( const string & input_text, const string & file_type )

inline

Function that checks if a string ends with the valid substring.

Parameters

input_text	Text inputed into the function, which is to be checked.
file_type	The substring which you wish to check if exists in the end of a given string.

Returns

true if the substring exists in the end of the given string, false otherwise.

    {
        if (input_text.length() >= file_type.length()) 
            {
            return (input_text.compare(input_text.length() - file_type.length(), file_type.length(), file_type) == 0);
            } 
        else 
            {
            return false;
            }
    }

GetHeight()

int Image::GetHeight ( ) const

inline

Gets the Height object.

    { 
        return height; 
    }

GetPixels()

void Image::GetPixels ( )

inline

Function that fills in the matrix of pixels.

    {
        for (int h = 0; h < height; h++)
        {
            for (int w = 0; w < width; w++)
            {
                int r, g, b;
                cin >> r >> g >> b;
                pixel[h][w].r = r;
                pixel[h][w].g = g;
                pixel[h][w].b = b;
            }
        }
    }

GetWidth()

int Image::GetWidth ( ) const

inline

Gets the Width object.

    { 
        return width; 
    }

IntToBin()

string Image::IntToBin ( int num, int bits = 8 )

inline

Function that receives an integer value and converts it to binary.

Parameters

num	Integer value to be converted into binary.
bits	The max size of the returned binary value.

Returns

a string containing the binary representation of the number received.

Base case: when there are no more bits to convert.

Determines the current bit in binary.

Recursive call to calculate the subsequent bits in binary.

    {
        if (bits == 0)
        {
            return "";
        }
        
        int bit_current = num % 2;
 
        string bit_subsequent = IntToBin(num / 2, bits - 1);
 
        return bit_subsequent + (bit_current == 0 ? '0' : '1');
    }

LiberatePixels()

void Image::LiberatePixels ( )

inline

Deallocates the memory previously allocated by the AllocatePixels() function, as well as the memory alocated by the array of the pixels' 'R', 'G' and 'B' values.

Deallocates the memory utilized by the array of the pixels' 'R', 'G' and 'B' values, used in the CreatePPM(), ReadPPM(), ShowArray(), CodeMsg() and DecodeMsg() functions.

    {
        if (pixel != nullptr)
        {
            for (int i = 0; i < height; i++)
            {
                delete[] pixel[i];
            }
            delete[] pixel;
            pixel = nullptr;
        }
        if (pixel_array != nullptr)
        {
            delete[] pixel_array;
            pixel_array = nullptr;
        }
    }

PrintPPM()

void Image::PrintPPM ( ) const

inline

Function that prints out the parameters of a PPM image. Mostly used for testing purposes.

    {
        cout << "\033[94mDados da imagem: \033[0m\n";
        cout << "\033[33m- Comprimento: \033[0m\n" << width << endl;
        cout << "\033[33m- Largura: \033[0m\n" << height << endl;
        cout << "\033[33m- Tipo de imagem: \033[0m\n" << img_type << endl;
        cout << "\033[33m- Valor máximo de cor: \033[0m\n" << max_color << endl;
        cout << "\033[33m- Valor RGB de cada pixel:\033[0m\n"; 
 
        for (int h = 0; h < height; h++)
        {
            for (int w = 0; w < width; w++)
            {
                Pixel p = pixel[h][w];
                cout << (int)p.r << " ";
                cout << (int)p.g << " ";
                cout << (int)p.b << "   ";
            }
            cout << endl;
        }
        cout << endl;
    }

ReadPPM()

bool Image::ReadPPM ( const string & file_name )

inline

Reads and dynamically stores the content of an image from a valid PPM file.

Parameters

file_name

The name of a PPM file previously stored inside the source folder, which will be read by the function.

Returns

true if the image was successfully read, false otherwise.

Tests if the file does exist inside the source folder.

Tests if the file is in fact a P3/PPM file by looking at it's content.

Memory allocation of the array of pixels, used in decodification and codification.

Reads and stores in an array the pixels' 'R', 'G' and 'B' values.

    {
        ifstream file(file_name);
        if (!file)
        {
            cerr << "\033[31mErro de leitura. O arquivo" << file_name << " não existe.\033[0m\n"; 
            return false;
        }
 
        string file_type;
        file >> file_type;
 
    
 
        if (file_type != "P3")
        {
            cerr << "\033[31mErro de leitura. O arquivo " << file_name << " não é uma imagem PPM no formato P3.\033[0m\n" << endl; 
            return false;
        }
 
        file >> width >> height >> max_color;
        size = width * height * 3;
 
        AllocatePixels();
 
        pixel_array = new int[size];
        int index = 0;
 
        for (int h = 0; h < height; h++)
        {
            for (int w = 0; w < width; w++)
            {
                int r, g, b;
                file >> r >> g >> b;
                pixel[h][w].r = r;
                pixel[h][w].g = g;
                pixel[h][w].b = b;
                pixel_array[index++] = r;
                pixel_array[index++] = g;
                pixel_array[index++] = b;
            }
        }
        file.close();
        return true;
    }

ShowArray()

void Image::ShowArray ( ) const

inline

Function that outputs a previously defined array of 'R', 'G' and 'B' values. Mostly used for testing purposes.

    {
        if (pixel_array == nullptr)
        {
            cout << "Array não inicializado." << endl;
            return;
        }
        for (int i = 0; i < size; i += 3)
        {
            cout << "Pixel [" << i / 3 << "]: R = " << pixel_array[i] << ", G = " << pixel_array[i + 1]
                 << ", B = " << pixel_array[i + 2] << endl;
        }
    }

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The documentation for this class was generated from the following file:

• D:/Usuario/OneDrive/Documentos/UFRN/ITP/esteganografia-lucas-e-malva/include/Image.h