Add contrast module (#463)

src/modules/Contrast/Module.js

@@ -0,0 +1,49 @@
+// /*
+// * Changes the Image Contrast
+// */
+
+module.exports = function Contrast(options, UI) {
+
+    options.contrast = options.contrast || 70
+    var output;
+
+    function draw(input, callback, progressObj) {
+
+        progressObj.stop(true);
+        progressObj.overrideFlag = true;
+
+        var step = this;
+
+        function changePixel(r, g, b, a) {
+            return [r, g, b, a]
+        }
+
+        function extraManipulation(pixels) {
+            pixels = require('./Contrast')(pixels, options.contrast)
+            return pixels
+        }
+
+        function output(image, datauri, mimetype) {
+
+            // This output is accessible by Image Sequencer
+            step.output = { src: datauri, format: mimetype };
+
+        }
+
+        return require('../_nomodule/PixelManipulation.js')(input, {
+            output: output,
+            changePixel: changePixel,
+            extraManipulation: extraManipulation,
+            format: input.format,
+            image: options.image,
+            callback: callback
+        });
+
+    }
+    return {
+        options: options,
+        draw: draw,
+        output: output,
+        UI: UI
+    }
+}