## 3 Proposed Method
### Adjustable Subsquares Properties Algorithm
concept of the adjustable subsquares properties algorithm is shown in Figure 1, while the properties of the method are described by the following relationships:  
\[SteepValue_{min}=\frac{L}{RGB_{max}}=\frac{25}{255}=0.09803921568 \tag{1}\]  
\[SteepValue=\left(\frac{\left(\frac{B*M}{RGB_{max}}\right)}{\left(B*2\right)} \right)=\left(\frac{\left(\frac{5*35}{255}\right)}{\left(5*2\right)}\right)=0.06 6862745098 \tag{2}\]  
\[SteepValue_{min[0,255]}=\frac{25}{255}*255=25 \tag{3}\]  
\[SteepValue_{[0,255]}=\left(\frac{\left(\frac{5*35}{255}\right)}{\left(5*2 \right)}\right)*255=17.5 \tag{4}\]  
\[SteepValue_{final}=SteepValue_{min}+SteepValue*DigitMultiplier \tag{5}\]  
where \(RGB_{max}\) is the maximum value in the RGB colour palette (\(255\)), \(L\) is the minimum value of the watermark embedding range in the value interval \(\left\langle 0;\ 255\right\rangle\), \(SteepValue_{min}\) is the minimum constant value added to the step calculating the value range for the digit, \(B\) is the maximum value of the digit of the used numeral system (senary), \(M\) is the maximum value of the range as a multiplier of the numeral system (senary) used, \(SteepValue\) is the constant value of the step calculating the value range for the digit, \(SteepValue_{[0,255]}\) is the constant value of the step calculating the range of values for the digit in the RGB value range, \(SteepValue_{min[0,255]}\) is the minimum value added to the step calculating the range of values for the digit in the RGB value range, \(DigitMultiplier\) is the multiplier for the digit specifying the lower- or upper-range value for the digit within the integer value range \(\left\langle 0;\ B*2\right\rangle\), and \(SteepValue_{final}\) is the total value of the step calculating the range of values for the digit. The system's basic purpose is to encode 16 ASCII characters using an image fragment of 128 \(\times\) 128 pixels from the range of Arabic numerals (0-9) and the letters of the English alphabet (A-Z), making for a total of 36 possible ASCII characters. Before the character concealment operation is performed, the image undergoes a change from the RGB colour palette to the YUV colour palette and a normalisation from the number range \(\left\langle 0;\ 255\right\rangle\) to the floating-point number range in \(\left\langle 0;\ 1\right\rangle\). ASCII characters are encoded on a 128 \(\times\) 128 pixel image in 32 \(\times\) 32 pixel blocks. The U and V colour channels are used to store the characters. The Y channel, which is the luminance channel, is trained to represent the original Y channel. The characters are encoded in the U and V channels in the senary numeral system. The U channel contains the older bit, while the other channel contains the younger bit. The value of the digit is stored in the interval \(\left\langle 0;\ 1\right\rangle\) with the step value calculated according to the previously presented relations. The value ranges on which the digits are encoded are shown in Table 1; the limiting value in the translation in the RGB colour palette value system is 182.5; it is the limiting value for digit 4; values greater than this will represent digit 5. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Digit** & **Value Range** & **RGB Value Range** \\ \hline
0 & \(\left\langle 0;\ 1666666666666\right\rangle\) & \(\left\langle 0;\ 42.5\right\rangle\) \\
1 & \(\left(0.166666666666\right\rangle\), \(0.30392156862\) & \(\left(42.5;\ 77.5\right)\) \\
2 & \(\left(0.30392156862;\ 0.44117647058\right)\) & \(\left(77.5;\ 112.5\right)\) \\
3 & \(\left(0.44117647058;\ 0.57843137254\right)\) & \(\left(112.5;\ 147.5\right)\) \\
4 & \(\left(0.57843137254;\ 0.71568627451\right)\) & \(\left(147.5;\ 182.5\right)\) \\
5 & \(\left(0.715686274515;\ 1\right)\) & \(\left(182.5;\ 255\right)\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Value ranges for encoding and decoding digits. At this point, it is worth noting that, according to the system components presented, two ANNs are used in the encoding process.