diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 90ebf2d5..02a75cd6 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -5,7 +5,7 @@ Happily accepting pull requests; to edit the core library, modify files in `./sr
 
 On ARM based devices, the `gl` module may require some libraries to be re-installed:
 
-`sudo apt-get install -y build-essential libxi-dev libglu1-mesa-dev libglew-dev pkg-config` -- see https://github.com/stackgl/headless-gl#ubuntudebian for more.
+`sudo apt-get install -y build-essential xserver-xorg-dev libxext-dev libxi-dev libglu1-mesa-dev libglew-dev pkg-config` -- see https://github.com/stackgl/headless-gl#ubuntudebian for more.
 
 Most contribution (we imagine) would be in the form of API-compatible modules, which need not be directly included.
 
diff --git a/src/modules/AddQR/QR.js b/src/modules/AddQR/QR.js
index 72de51ec..b23e3ef7 100644
--- a/src/modules/AddQR/QR.js
+++ b/src/modules/AddQR/QR.js
@@ -32,7 +32,7 @@ module.exports = exports = function (options, pixels, oldPixels, callback) {
           }
 
           else {
-            pixelSetter(m, n, [qrPixels.get(m, n, 0), qrPixels.get(m, n, 1), qrPixels.get(m, n, 2), qrPixels.get(m, n, 3)], pixels);
+            pixelSetter(m, n, [oldPixels.get(m, n, 0), oldPixels.get(m, n, 1), oldPixels.get(m, n, 2), oldPixels.get(m, n, 3)], pixels);
           }
 
         }
diff --git a/src/modules/DrawRectangle/DrawRectangle.js b/src/modules/DrawRectangle/DrawRectangle.js
index a38ac4bd..ee9bf114 100644
--- a/src/modules/DrawRectangle/DrawRectangle.js
+++ b/src/modules/DrawRectangle/DrawRectangle.js
@@ -19,7 +19,7 @@ module.exports = exports = function(pixels, options){
     for (var n = startX; n <= endX + thickness; n++){
       for (var k = startY; k <= endY + thickness; k++){
 
-        pixelSetter(n, k, color, pixels); //to remove 4th channel - pixels.set(n, k, 3, color[3]);
+        pixelSetter(n, k, [color[0], color[1], color[2]], pixels); //to remove 4th channel - pixels.set(n, k, 3, color[3]);
       }
     }
   };
diff --git a/src/modules/GridOverlay/GridOverlay.js b/src/modules/GridOverlay/GridOverlay.js
index 82f95340..2a28bf8c 100644
--- a/src/modules/GridOverlay/GridOverlay.js
+++ b/src/modules/GridOverlay/GridOverlay.js
@@ -2,11 +2,11 @@ module.exports = exports = function(pixels, options){
   var defaults = require('./../../util/getDefaults.js')(require('./info.json'));
   const pixelSetter = require('../../util/pixelSetter.js');
 
-  if(Number(options.x)==0){
+  if(Number(options.x) == 0){
     options.x = 1;
-  } 
-  if( Number(options.y)==0) {
-    options.y =1;
+  }
+  if( Number(options.y) == 0) {
+    options.y = 1;
   }
 
   options.x = Math.abs(Number(options.x)) || defaults.x;
@@ -17,14 +17,14 @@ module.exports = exports = function(pixels, options){
 
   for(var x = 0; x < pixels.shape[0]; x += options.x){
     for(var y = 0 ; y < pixels.shape[1]; y++){
-      pixelSetter(x, y, color, pixels); // to remove 4th channel - pixels.set(x, y, 3, color[3]);
+      pixelSetter(x, y, [color[0], color[1], color[2]], pixels); // to remove 4th channel - pixels.set(x, y, 3, color[3]);
                 
     }
   }
     
   for(var y = 0; y < pixels.shape[1]; y += options.y){
     for(var x = 0 ; x < pixels.shape[0]; x++){
-      pixelSetter(x, y, color, pixels); // to remove 4th channel - pixels.set(x, y, 3, color[3]);
+      pixelSetter(x, y, [color[0], color[1], color[2]], pixels); // to remove 4th channel - pixels.set(x, y, 3, color[3]);
 
     }
   }