Added colormap application to single channel images.

cpp/include/Image.hpp

@@ -21,6 +21,12 @@ class Image {
             LANCZOS     ///< Lanczos filtering interpolation.
         };
 
+        /// @brief Colormaps LUTs.
+        struct Colormap {
+            /// @brief MATLAB's parula colormap. 256x3 values : R0G0B0, R1G1B1, ...
+            static constexpr unsigned char PARULA_256[256*3] = {62,38,168 ,62,39,172 ,63,40,175 ,63,41,178 ,64,42,180 ,64,43,183 ,65,44,186 ,65,45,189 ,66,46,191 ,66,47,194 ,67,48,197 ,67,49,200 ,67,50,202 ,68,51,205 ,68,52,208 ,69,53,210 ,69,55,213 ,69,56,215 ,70,57,217 ,70,58,220 ,70,59,222 ,70,61,224 ,71,62,225 ,71,63,227 ,71,65,229 ,71,66,230 ,71,68,232 ,71,69,233 ,71,70,235 ,72,72,236 ,72,73,237 ,72,75,238 ,72,76,240 ,72,78,241 ,72,79,242 ,72,80,243 ,72,82,244 ,72,83,245 ,72,84,246 ,71,86,247 ,71,87,247 ,71,89,248 ,71,90,249 ,71,91,250 ,71,93,250 ,70,94,251 ,70,96,251 ,70,97,252 ,69,98,252 ,69,100,253 ,68,101,253 ,67,103,253 ,67,104,254 ,66,106,254 ,65,107,254 ,64,109,254 ,63,110,255 ,62,112,255 ,60,113,255 ,59,115,255 ,57,116,255 ,56,118,254 ,54,119,254 ,53,121,253 ,51,122,253 ,50,124,252 ,49,125,252 ,48,127,251 ,47,128,250 ,47,130,250 ,46,131,249 ,46,132,248 ,46,134,248 ,46,135,247 ,45,136,246 ,45,138,245 ,45,139,244 ,45,140,243 ,45,142,242 ,44,143,241 ,44,144,240 ,43,145,239 ,42,147,238 ,41,148,237 ,40,149,236 ,39,151,235 ,39,152,234 ,38,153,233 ,38,154,232 ,37,155,232 ,37,156,231 ,36,158,230 ,36,159,229 ,35,160,229 ,35,161,228 ,34,162,228 ,33,163,227 ,32,165,227 ,31,166,226 ,30,167,225 ,29,168,225 ,29,169,224 ,28,170,223 ,27,171,222 ,26,172,221 ,25,173,220 ,23,174,218 ,22,175,217 ,20,176,216 ,18,177,214 ,16,178,213 ,14,179,212 ,11,179,210 ,8,180,209 ,6,181,207 ,4,182,206 ,2,183,204 ,1,183,202 ,0,184,201 ,0,185,199 ,0,186,198 ,1,186,196 ,2,187,194 ,4,187,193 ,6,188,191 ,9,189,189 ,13,189,188 ,16,190,186 ,20,190,184 ,23,191,182 ,26,192,181 ,29,192,179 ,32,193,177 ,35,193,175 ,37,194,174 ,39,194,172 ,41,195,170 ,43,195,168 ,44,196,166 ,46,196,165 ,47,197,163 ,49,197,161 ,50,198,159 ,51,199,157 ,53,199,155 ,54,200,153 ,56,200,150 ,57,201,148 ,59,201,146 ,61,202,144 ,64,202,141 ,66,202,139 ,69,203,137 ,72,203,134 ,75,203,132 ,78,204,129 ,81,204,127 ,84,204,124 ,87,204,122 ,90,204,119 ,94,205,116 ,97,205,114 ,100,205,111 ,103,205,108 ,107,205,105 ,110,205,102 ,114,205,100 ,118,204,97 ,121,204,94 ,125,204,91 ,129,204,89 ,132,204,86 ,136,203,83 ,139,203,81 ,143,203,78 ,147,202,75 ,150,202,72 ,154,201,70 ,157,201,67 ,161,200,64 ,164,200,62 ,167,199,59 ,171,199,57 ,174,198,55 ,178,198,53 ,181,197,51 ,184,196,49 ,187,196,47 ,190,195,45 ,194,195,44 ,197,194,42 ,200,193,41 ,203,193,40 ,206,192,39 ,208,191,39 ,211,191,39 ,214,190,39 ,217,190,40 ,219,189,40 ,222,188,41 ,225,188,42 ,227,188,43 ,230,187,45 ,232,187,46 ,234,186,48 ,236,186,50 ,239,186,53 ,241,186,55 ,243,186,57 ,245,186,59 ,247,186,61 ,249,186,62 ,251,187,62 ,252,188,62 ,254,189,61 ,254,190,60 ,254,192,59 ,254,193,58 ,254,194,57 ,254,196,56 ,254,197,55 ,254,199,53 ,254,200,52 ,254,202,51 ,253,203,50 ,253,205,49 ,253,206,49 ,252,208,48 ,251,210,47 ,251,211,46 ,250,213,46 ,249,214,45 ,249,216,44 ,248,217,43 ,247,219,42 ,247,221,42 ,246,222,41 ,246,224,40 ,245,225,40 ,245,227,39 ,245,229,38 ,245,230,38 ,245,232,37 ,245,233,36 ,245,235,35 ,245,236,34 ,245,238,33 ,246,239,32 ,246,241,31 ,246,242,30 ,247,244,28 ,247,245,27 ,248,247,26 ,248,248,24 ,249,249,22 ,249,251,21};
+        };
+
         /// @brief Initializes the image with the given width, height, and optionally depth. Warning : the values are uninitialized.
         /// @param width_   Width of the image.
         /// @param height_  Height of the image.
@@ -129,6 +135,11 @@ class Image {
         /// @return A reference to the image.
         Image & HistogramNormalize(int downsampling_factor=1);
 
+        /// @brief Applies a colormap to the image. After applying the colormap, the image will be 3-channel (RGB). If the image is not single-channel, a unnchanged copy of the image is returned.
+        /// @param colormap Array of 256*3 values, representing the RGB values of the colormap. Order is R0, G0, B0, R1, G1, B1, etc.
+        /// @return Reference to the image.
+        Image Colorized(unsigned char const* colormap) const;
+
         /// @brief Computes the histogram of the image.
         /// All channels are used to compute the histogram. If the downscale factor is a multiple of the number of channels, the histogram will be skewed and will only use the first channel.
         /// @param downscale_factor Factor by which the image is downsampled before computing the histogram.

cpp/src/Image.cpp

@@ -161,6 +161,17 @@ Image & Image::HistogramNormalize(int downsampling_factor) {
     return *this;
 }
 
+Image Image::Colorized(unsigned char const* colormap) const {
+    if (depth != 1)
+        return *this;
+    Image colorized(width, height, 3);
+    for(int i = 0 ; i < height ; i++)
+        for(int j = 0 ; j < width ; j++)
+            for(int c = 0 ; c < 3 ; c++)
+                colorized.SetPixelValue(i, j, c, colormap[3*GetPixelValue(i, j) + c]);
+    return colorized;
+}
+
 std::vector<uint64_t> Image::ComputeHistogram(int downsampling_factor) const {
     std::vector<uint64_t> hist(256, 0);
     for(int i = 0 ; i < width*height*depth ; i += downsampling_factor)

cpp/src/tests.cpp

@@ -300,6 +300,10 @@ int main() {
             Image image_luma = image.LumaREC709();
             image_gray.Save("venise_gray.jpg");
             image_luma.Save("venise_luma.jpg");
+
+            std::cout << "Colormap application\n";
+            Image image_parula = image_luma.Colorized(Image::Colormap::PARULA_256);
+            image_parula.Save("venise_parula.jpg");
         }
 
         {