Cleaned up and improved OCR operation

src/core/operations/OpticalCharacterRecognition.mjs

@@ -0,0 +1,77 @@
+/**
+ * @author n1474335 [n1474335@gmail.com]
+ * @author mshwed [m@ttshwed.com]
+ * @copyright Crown Copyright 2019
+ * @license Apache-2.0
+ */
+
+import Operation from "../Operation.mjs";
+import OperationError from "../errors/OperationError.mjs";
+import { isImage } from "../lib/FileType.mjs";
+import { toBase64 } from "../lib/Base64.mjs";
+import { isWorkerEnvironment } from "../Utils.mjs";
+
+import Tesseract from "tesseract.js";
+const { TesseractWorker } = Tesseract;
+
+/**
+ * Optical Character Recognition operation
+ */
+class OpticalCharacterRecognition extends Operation {
+
+    /**
+     * OpticalCharacterRecognition constructor
+     */
+    constructor() {
+        super();
+
+        this.name = "Optical Character Recognition";
+        this.module = "Image";
+        this.description = "Optical character recognition or optical character reader (OCR) is the mechanical or electronic conversion of images of typed, handwritten or printed text into machine-encoded text.<br><br>Supported image formats: png, jpg, bmp, pbm.";
+        this.infoURL = "https://wikipedia.org/wiki/Optical_character_recognition";
+        this.inputType = "ArrayBuffer";
+        this.outputType = "string";
+        this.args = [
+            {
+                name: "Show confidence",
+                type: "boolean",
+                value: true
+            }
+        ];
+    }
+
+    /**
+     * @param {ArrayBuffer} input
+     * @param {Object[]} args
+     * @returns {string}
+     */
+    async run(input, args) {
+        const [showConfidence] = args;
+
+        const type = isImage(input);
+        if (!type) {
+            throw new OperationError("Invalid File Type");
+        }
+
+        try {
+            const image = `data:${type};base64,${toBase64(input)}`;
+            const worker = new TesseractWorker();
+            const result = await worker.recognize(image)
+                .progress(progress => {
+                    if (isWorkerEnvironment()) {
+                        self.sendStatusMessage(`Status: ${progress.status} - ${(parseFloat(progress.progress)*100).toFixed(2)}%`);
+                    }
+                });
+
+            if (showConfidence) {
+                return `Confidence: ${result.confidence}%\n\n${result.text}`;
+            } else {
+                return result.text;
+            }
+        } catch (err) {
+            throw new OperationError(`Error performing OCR on image. (${err})`);
+        }
+    }
+}
+
+export default OpticalCharacterRecognition;