diff --git a/build.py b/build.py
index 1caaa60..1e517fb 100755
--- a/build.py
+++ b/build.py
@@ -17,7 +17,17 @@
 
 def sources():
     return [os.path.join(base, f) for base, folders, files in \
-        os.walk(input_path) for f in files if f.endswith('.js')]
+        os.walk(input_path) for f in files if 'include' in sys.argv and includes(os.path.join(base, f)) or 'include' not in sys.argv and f.endswith('.js')]
+
+def includes(file):
+    if '/filters/' in file:
+        if 'common' in file:
+            return True
+        for name in sys.argv:
+            if name in file:
+                return True
+        return False
+    return True
 
 def compile(sources):
     return '\n'.join('// %s\n%s' % (path, open(path).read()) for path in sources)
diff --git a/src/core/canvas.js b/src/core/canvas.js
index b9bc4e1..18e0d0b 100644
--- a/src/core/canvas.js
+++ b/src/core/canvas.js
@@ -129,8 +129,8 @@ function wrap(func) {
     };
 }
 
-exports.canvas = function() {
-    var canvas = document.createElement('canvas');
+exports.canvas = function(canvas) {
+    canvas = canvas instanceof window.HTMLCanvasElement ? canvas : document.createElement('canvas');
     try {
         gl = canvas.getContext('experimental-webgl', { premultipliedAlpha: false });
     } catch (e) {
@@ -156,29 +156,29 @@ exports.canvas = function() {
     canvas.getPixelArray = wrap(getPixelArray);
 
     // Filter methods
-    canvas.brightnessContrast = wrap(brightnessContrast);
-    canvas.hexagonalPixelate = wrap(hexagonalPixelate);
-    canvas.hueSaturation = wrap(hueSaturation);
-    canvas.colorHalftone = wrap(colorHalftone);
-    canvas.triangleBlur = wrap(triangleBlur);
-    canvas.unsharpMask = wrap(unsharpMask);
-    canvas.perspective = wrap(perspective);
-    canvas.matrixWarp = wrap(matrixWarp);
-    canvas.bulgePinch = wrap(bulgePinch);
-    canvas.tiltShift = wrap(tiltShift);
-    canvas.dotScreen = wrap(dotScreen);
-    canvas.edgeWork = wrap(edgeWork);
-    canvas.lensBlur = wrap(lensBlur);
-    canvas.zoomBlur = wrap(zoomBlur);
-    canvas.noise = wrap(noise);
-    canvas.denoise = wrap(denoise);
-    canvas.curves = wrap(curves);
-    canvas.swirl = wrap(swirl);
-    canvas.ink = wrap(ink);
-    canvas.vignette = wrap(vignette);
-    canvas.vibrance = wrap(vibrance);
-    canvas.sepia = wrap(sepia);
+    typeof brightnessContrast !== 'undefined' && (canvas.brightnessContrast = wrap(brightnessContrast));
+    typeof hexagonalPixelate !== 'undefined' && (canvas.hexagonalPixelate = wrap(hexagonalPixelate));
+    typeof hueSaturation !== 'undefined' && (canvas.hueSaturation = wrap(hueSaturation));
+    typeof colorHalftone !== 'undefined' && (canvas.colorHalftone = wrap(colorHalftone));
+    typeof triangleBlur !== 'undefined' && (canvas.triangleBlur = wrap(triangleBlur));
+    typeof unsharpMask !== 'undefined' && (canvas.unsharpMask = wrap(unsharpMask));
+    typeof perspective !== 'undefined' && (canvas.perspective = wrap(perspective));
+    typeof matrixWarp !== 'undefined' && (canvas.matrixWarp = wrap(matrixWarp));
+    typeof bulgePinch !== 'undefined' && (canvas.bulgePinch = wrap(bulgePinch));
+    typeof tiltShift !== 'undefined' && (canvas.tiltShift = wrap(tiltShift));
+    typeof dotScreen !== 'undefined' && (canvas.dotScreen = wrap(dotScreen));
+    typeof edgeWork !== 'undefined' && (canvas.edgeWork = wrap(edgeWork));
+    typeof lensBlur !== 'undefined' && (canvas.lensBlur = wrap(lensBlur));
+    typeof zoomBlur !== 'undefined' && (canvas.zoomBlur = wrap(zoomBlur));
+    typeof noise !== 'undefined' && (canvas.noise = wrap(noise));
+    typeof denoise !== 'undefined' && (canvas.denoise = wrap(denoise));
+    typeof curves !== 'undefined' && (canvas.curves = wrap(curves));
+    typeof swirl !== 'undefined' && (canvas.swirl = wrap(swirl));
+    typeof ink !== 'undefined' && (canvas.ink = wrap(ink));
+    typeof vignette !== 'undefined' && (canvas.vignette = wrap(vignette));
+    typeof vibrance !== 'undefined' && (canvas.vibrance = wrap(vibrance));
+    typeof sepia !== 'undefined' && (canvas.sepia = wrap(sepia));
 
     return canvas;
 };
-exports.splineInterpolate = splineInterpolate;
+typeof splineInterpolate !== 'undefined' && (exports.splineInterpolate = splineInterpolate);