add posterization

flake.nix

@@ -27,6 +27,8 @@
 
       devShells.default = pkgs.mkShell {
         buildInputs = [
+
+          # building seamly2d and valentina
           pkgs.qt5.full
           pkgs.qtcreator
           pkgs.libGL
@@ -35,6 +37,27 @@
           pkgs.qt5.qtxmlpatterns
           pkgs.qt5.qt3d
           pkgs.qt5.qmake
+
+          # poster
+          pkgs.imagemagick
+          pkgs.ghostscript
+          # A4 is 2480 x 3508 Pixel
+          # A4 with 100px space on top bottom left and right is :  2280 x 3308 Pixel
+          (pkgs.writers.writeBashBin "posterize" ''
+            ${pkgs.imagemagick}/bin/convert -density 300 -depth 8 -quality 85 input.pdf input.png
+            ${pkgs.imagemagick}/bin/convert input.png -crop 2280x3308  +repage  output_a4_%02d.png
+            for file in output_a4_*
+            do
+              ${pkgs.imagemagick}/bin/convert \
+                $file \
+                -gravity center \
+                -background gray \
+                -extent 2480x3508 \
+                final_$file
+            done
+            ${pkgs.imagemagick}/bin/convert final_*.png -quality 100 output.pdf
+            rm -rf *.png
+          '')
         ];
       };