## 4 Methods  
We considered 35 hand-designed and 33 CNN-based descriptors as detailed in Sections 4.1-4.2 (see also Tables 2 and 3 for a round-up). We subdivided the hand-designed methods into three subgroups:  
* Purely spectral descriptors (colour descriptors; Section 4.1.1);
* Grey-scale texture descriptors (Section 4.1.2);
* Colour texture descriptors (Section 4.1.3).  
\begin{table}
\begin{tabular}{l l l l} \hline \hline \multicolumn{1}{c}{**Method**} & \multicolumn{1}{c}{**Variant**} & \multicolumn{1}{c}{**Abbreviation**} & \multicolumn{1}{c}{**No. of Features**} \\ \hline \multicolumn{5}{l}{_Purely spectral descriptors_} \\ \hline Mean of each channel & & Mean & 3 \\ Mean and std. dev.of each channel & & Mean + Std & 6 \\ Mean and moms.from 2 th to 5 th of each ch. & & Mean + Moms & 15 \\ Quartiles of each channel & & Quartiles & 9 \\
256-bin Marginal Histogram of each channel & & Marginal-Hists-256 & 768 \\
10-bin joint colour Histogram & & Full-Hist-10 & 1000 \\ \hline \multicolumn{5}{l}{_Key-scale texture descriptors_} \\ \hline Completed Local Binary Patterns & Rotation-invariant & CLBP & 324 \\ Gradient-based Local Binary Patterns & Rotation-invariant & GLBP & 108 \\ Improved Local Binary Patterns & Rotation-invariant & ILBP & 213 \\ Local Binary Patterns & Rotation-invariant & LBP & 108 \\ Local Ternary Patterns & Rotation-invariant & LTP & 216 \\ Texture Spectrum & Rotation-invariant & TS & 2502 \\ Grey-level Co-occurrence Matrices & & GLCM & 60 \\ Grey-level Co-occurrence Matrices & & GLCM\({}^{DFT}\) & 60 \\ Gabor features & & Gabor & 70 \\ Gabor features & Rotation-invariant & Gabor\({}^{DFT}\) & 70 \\ Gabor features & Contrast-normalised & Gabor\({}_{cn}\) & 70 \\ Gabor features & Rot.-inv.and ctr.-norm. & Gabor\({}^{DFT}_{cn}\) & 70 \\ Image Patch-Based Classifier & Joint & IPBC-J & 4096 \\ Histograms of Oriented Gradients & & HOG & 768 \\ Dense SIFT & BoVW aggregation & SIFT-BoVW & 4096 \\ Dense SIFT & VLAD aggregation & SIFT-VLAD & 4608 \\ VZClassifier & MR8 filters & VZ-MR8 & 4096 \\ Wavelet Statistical and Co-occurrence Features & Haar wavelet & WSF + WCF\({}_{har}\) & 84 \\ Wavelet Statistical and Co-occurrence Features & Bi-orthogonal wavelet & WSF + WCF\({}_{bir22}\) & 84 \\ \hline \multicolumn{5}{l}{_Colour texture descriptors_} \\ \hline Improved Opponent Colour LBP & Rotation-invariant & IOLBP & 1287 \\ Integrative Co-occurrence Matrices & & ICM & 360 \\ Integrative Co-occurrence Matrices & Rotation-invariant & ICM\({}^{DFT}\) & 360 \\ Local Binary Patterns + Local Colour Contrast & Rotation-invariant LBP & LBP + LCC & 876 \\ Local Colour Vector Binary Patterns & Rotation-invariant & LCVBP & 432 \\ Opponent Colour Local Binary Patterns & Rotation-invariant & OCLBP & 648 \\ Opponent Gabor features & & OppGabor & 630 \\ Opponent Gabor features & Contrast-normalised & OppGabor\({}_{cn}\) & 630 \\ Opponent Gabor features & Rotation-invariant & OppGabor\({}^{DFT}_{cn}\) & 630 \\ Opponent Gabor features & Rot.-inv. and ctr.-norm. & OppGabor\({}^{DFT}_{cn}\) & 630 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Summary table of the hand-crafted image descriptors used in the experiments. VLAD, Vectors of Locally-Aggregated Descriptors.  
Figure 10: Group #10: Non-stationary textures acquired under multiple variations in the imaging conditions (Section 3.2.10).