(#68) Moved scaling of images into separate file

Author: s1hofmann

lib/provider/opencv/scale-image.function.spec.ts

@@ -0,0 +1,40 @@
+import * as path from "path";
+import { ImageProcessor } from "./image-processor.class";
+import { ImageReader } from "./image-reader.class";
+import { scaleImage } from "./scale-image.function";
+
+describe("scaleImage", () => {
+  it.each([[0.5], [1.5]])("should scale an image correctly by factor %f", async (scaleFactor) => {
+    // GIVEN
+    const imageLoader = new ImageReader();
+    const pathToinput = path.resolve(__dirname, "./__mocks__/mouse.png");
+    const inputImage = await imageLoader.load(pathToinput);
+    const inputMat = await ImageProcessor.fromImageWithoutAlphaChannel(inputImage);
+    const expectedWidth = Math.floor(inputMat.cols * scaleFactor);
+    const expectedHeight = Math.floor(inputMat.rows * scaleFactor);
+
+    // WHEN
+    const result = await scaleImage(inputMat, scaleFactor);
+
+    // THEN
+    expect(result.rows).toBe(expectedHeight);
+    expect(result.cols).toBe(expectedWidth);
+  });
+
+  it.each([[0], [-0.25]])("should keep scale if factor <= 0: Scale %f", async (scaleFactor) => {
+    // GIVEN
+    const imageLoader = new ImageReader();
+    const pathToinput = path.resolve(__dirname, "./__mocks__/mouse.png");
+    const inputImage = await imageLoader.load(pathToinput);
+    const inputMat = await ImageProcessor.fromImageWithoutAlphaChannel(inputImage);
+    const expectedWidth = inputMat.cols;
+    const expectedHeight = inputMat.rows;
+
+    // WHEN
+    const result = await scaleImage(inputMat, scaleFactor);
+
+    // THEN
+    expect(result.rows).toBe(expectedHeight);
+    expect(result.cols).toBe(expectedWidth);
+  });
+});

lib/provider/opencv/scale-image.function.ts

@@ -0,0 +1,8 @@
+import * as cv from "opencv4nodejs-prebuilt";
+
+export const scaleImage = async (image: cv.Mat, scaleFactor: number): Promise<cv.Mat> => {
+  const minScaleFactor = (scaleFactor <= 0.0) ? 1.0 : scaleFactor;
+  const scaledRows = Math.floor(image.rows * minScaleFactor);
+  const scaledCols = Math.floor(image.cols * minScaleFactor);
+  return image.resizeAsync(scaledRows, scaledCols, 0, 0, cv.INTER_AREA);
+};