# Color Texture Image Complexity--EEG-Sensed Human Brain Perception vs. Computed Measures
## 7 Experimental Results
### Image Complexity Measures vs. Subjective Evaluation--Correlation Analysis
#### 7.2.2 Fractal Images  
When considering _Frac_ images, significant correlations were observed (\(r>0.2\)), except P2 and P7 participants--who considered the textures predominantly as medium complexity. Almost half of the participants correlate in answers (46%) and further, participants answers correlate more with the CFD levels, as compared to CE levels (Table 4). For five subjects, there is a significant resemblance between the participants' answers and the complexity levels expressed by CE and CFD: CE-P3 (\(\rho=0.35\)), CE-P4 (\(\rho=0.38\)), CE-P8 (\(\rho=0.38\)), CFD-P1 (\(\rho=0.8\)), CFD-P4 (\(\rho=0.65\)), and CFD-P6 (\(\rho=0.46\)). Between participants, the highest correlations are observed between P1 and P3 (\(\rho=0.51\)) and P1 and P4 (\(\rho=0.53\)).  
\begin{table}
\begin{tabular}{c c c c c} \hline  & & \multicolumn{3}{c}{_Nat_} \\ \hline Complexity level & 1: low & 2: medium & 3: high \\ \hline CE & 7.33–10.34 & 10.34–13.35 & 13.35–16.37 \\ CFD & 1.89–2.59 & 2.59–3.28 & 3.28–3.98 \\ \hline  & & \multicolumn{3}{c}{_Frac_} \\ \hline Complexity level & 1: low & 2: medium & 3: high \\ \hline CE & 16.45–16.9 & 16.9–17.37 & 17.37–17.84 \\ CFD & 2.03–2.73 & 2.73–3.42 & 3.42–4.12 \\ \hline \end{tabular}
\end{table}
Table 2: CE and CFD levels for _Nat_ and _Frac_ images.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline  & **P1** & **P2** & **P3** & **P4** & **P5** & **P6** & **P7** & **P8** \\ \hline CE & **0.41** & & 0.35 & 0.23 & **0.47** & 0.34 & & 0.34 \\ \hline CFD & 0.33 & **0.47** & 0.21 & & 0.27 & 0.36 & 0.27 \\ \hline P1 & 0.26 & & **0.4** & 0.33 & 0.35 & 0.34 \\ \hline P2 & & & **0.48** & & 0.3 & 0.24 & 0.32 \\ \hline P3 & & & & & 0.23 & 0.28 & 0.2 \\ \hline P4 & & & & & 0.23 & & \\ \hline P5 & & & & & & 0.26 \\ \hline P6 & & & & & & 0.37 \\ \hline P7 & & & & & & \\ \hline P8 & & & & & & \\ \hline \end{tabular}
\end{table}
Table 3: CE, CFD levels versus Participants answers—correlation matrix for _Nat_ images. Only significant Pearson correlation values are presented: \(r>0.2\) with \(\alpha=0.05\). Highest values are highlighted in bold.  
Significant negative correlations are observed for participant P5 in relation to the computed measures and other participants, and it is explained by the fact that the participant merely considered low complexity for the fractal textures, based on personal reasoning, attractiveness, emotions, memories, and imagination, which were not felt for participant P5 when viewing the synthetic fractal textures due to the lack of relation to known forms.  
These results highlight that the internal reasoning on complexity is subjective for individuals, and the variations between individuals are higher for _Frac_ images, probably because the texture contained does not relate to known forms and the decision on complexity involves more imaginatory actions requiring longer time and intense processes, which may obstruct the observer in its reasoning process. Further, for _Frac_ images, participant reasoning is closer to the color fractal dimension estimation, then to color entropy, which is curious to observe since CE and CFD measures are highly correlated, as seen in Figure 4b. The subjective responses not detected as significantly correlated with the analysis measures, most probably relate to the other human internal reasoning mechanisms, as described in Section 7.1, which does not relate to criteria detectable by image texture analysis.