Add image opacity operation

src/core/config/Categories.json

@@ -367,7 +367,8 @@
             "Invert Image",
             "Flip Image",
             "Crop Image",
-            "Image Brightness / Contrast"
+            "Image Brightness / Contrast",
+            "Image Opacity"
         ]
     },
     {

src/core/operations/ImageOpacity.mjs

@@ -0,0 +1,83 @@
+/**
+ * @author j433866 [j433866@gmail.com]
+ * @copyright Crown Copyright 2019
+ * @license Apache-2.0
+ */
+
+import Operation from "../Operation";
+import OperationError from "../errors/OperationError";
+import Magic from "../lib/Magic";
+import { toBase64 } from "../lib/Base64.mjs";
+import jimp from "jimp";
+
+/**
+ * Image Opacity operation
+ */
+class ImageOpacity extends Operation {
+
+    /**
+     * ImageOpacity constructor
+     */
+    constructor() {
+        super();
+
+        this.name = "Image Opacity";
+        this.module = "Image";
+        this.description = "Adjust the opacity of an image.";
+        this.infoURL = "";
+        this.inputType = "byteArray";
+        this.outputType = "byteArray";
+        this.presentType = "html";
+        this.args = [
+            {
+                name: "Opacity (%)",
+                type: "number",
+                value: 100,
+                min: 0,
+                max: 100
+            }
+        ];
+    }
+
+    /**
+     * @param {byteArray} input
+     * @param {Object[]} args
+     * @returns {byteArray}
+     */
+    async run(input, args) {
+        const [opacity] = args;
+        const type = Magic.magicFileType(input);
+        if (!type || type.mime.indexOf("image") !== 0){
+            throw new OperationError("Invalid file type.");
+        }
+
+        const image = await jimp.read(Buffer.from(input));
+        image.opacity(opacity / 100);
+
+        const imageBuffer = await image.getBufferAsync(jimp.MIME_PNG);
+        return [...imageBuffer];
+    }
+
+    /**
+     * Displays the image using HTML for web apps
+     * @param {byteArray} data
+     * @returns {html}
+     */
+    present(data) {
+        if (!data.length) return "";
+
+        let dataURI = "data:";
+        const type = Magic.magicFileType(data);
+        if (type && type.mime.indexOf("image") === 0){
+            dataURI += type.mime + ";";
+        } else {
+            throw new OperationError("Invalid file type");
+        }
+        dataURI += "base64," + toBase64(data);
+
+        return "<img src='" + dataURI + "'>";
+    }
+
+}
+
+export default ImageOpacity;