Add option to maintain aspect ratio on resize (#971)

* Add option to resize one dimension and maintain aspect ratio.

* Update src/utils/image.js

Reduce function calls for optimisation.

Co-authored-by: Joshua Lochner <[email protected]>

* Optimise image utils tests.

* nullish dimension may be `null`, `undefined`, or `-1`

---------

Co-authored-by: Joshua Lochner <[email protected]>

Author: BritishWerewolf

src/utils/core.js

@@ -1,10 +1,10 @@
 
 /**
  * @file Core utility functions/classes for Transformers.js.
- * 
+ *
  * These are only used internally, meaning an end-user shouldn't
  * need to access anything here.
- * 
+ *
  * @module utils/core
  */
 
@@ -65,7 +65,7 @@ export function escapeRegExp(string) {
  * Check if a value is a typed array.
  * @param {*} val The value to check.
  * @returns {boolean} True if the value is a `TypedArray`, false otherwise.
- * 
+ *
  * Adapted from https://stackoverflow.com/a/71091338/13989043
  */
 export function isTypedArray(val) {
@@ -82,6 +82,15 @@ export function isIntegralNumber(x) {
     return Number.isInteger(x) || typeof x === 'bigint'
 }
 
+/**
+ * Determine if a provided width or height is nullish.
+ * @param {*} x The value to check.
+ * @returns {boolean} True if the value is `null`, `undefined` or `-1`, false otherwise.
+ */
+export function isNullishDimension(x) {
+    return x === null || x === undefined || x === -1;
+}
+
 /**
  * Calculates the dimensions of a nested array.
  *
@@ -151,9 +160,9 @@ export function calculateReflectOffset(i, w) {
 }
 
 /**
- * 
- * @param {Object} o 
- * @param {string[]} props 
+ *
+ * @param {Object} o
+ * @param {string[]} props
  * @returns {Object}
  */
 export function pick(o, props) {
@@ -170,7 +179,7 @@ export function pick(o, props) {
 /**
  * Calculate the length of a string, taking multi-byte characters into account.
  * This mimics the behavior of Python's `len` function.
- * @param {string} s The string to calculate the length of. 
+ * @param {string} s The string to calculate the length of.
  * @returns {number} The length of the string.
  */
 export function len(s) {

src/utils/image.js

@@ -1,13 +1,14 @@
 
 /**
- * @file Helper module for image processing. 
- * 
- * These functions and classes are only used internally, 
+ * @file Helper module for image processing.
+ *
+ * These functions and classes are only used internally,
  * meaning an end-user shouldn't need to access anything here.
- * 
+ *
  * @module utils/image
  */
 
+import { isNullishDimension } from './core.js';
 import { getFile } from './hub.js';
 import { env } from '../env.js';
 import { Tensor } from './tensor.js';
@@ -91,7 +92,7 @@ export class RawImage {
         this.channels = channels;
     }
 
-    /** 
+    /**
      * Returns the size of the image (width, height).
      * @returns {[number, number]} The size of the image (width, height).
      */
@@ -101,9 +102,9 @@ export class RawImage {
 
     /**
      * Helper method for reading an image from a variety of input types.
-     * @param {RawImage|string|URL} input 
+     * @param {RawImage|string|URL} input
      * @returns The image object.
-     * 
+     *
      * **Example:** Read image from a URL.
      * ```javascript
      * let image = await RawImage.read('https://huggingface.co/datasets/Xenova/transformers.js-docs/resolve/main/football-match.jpg');
@@ -181,7 +182,7 @@ export class RawImage {
 
     /**
      * Helper method to create a new Image from a tensor
-     * @param {Tensor} tensor 
+     * @param {Tensor} tensor
      */
     static fromTensor(tensor, channel_format = 'CHW') {
         if (tensor.dims.length !== 3) {
@@ -306,8 +307,8 @@ export class RawImage {
 
     /**
      * Resize the image to the given dimensions. This method uses the canvas API to perform the resizing.
-     * @param {number} width The width of the new image.
-     * @param {number} height The height of the new image.
+     * @param {number} width The width of the new image. `null` or `-1` will preserve the aspect ratio.
+     * @param {number} height The height of the new image. `null` or `-1` will preserve the aspect ratio.
      * @param {Object} options Additional options for resizing.
      * @param {0|1|2|3|4|5|string} [options.resample] The resampling method to use.
      * @returns {Promise<RawImage>} `this` to support chaining.
@@ -324,6 +325,20 @@ export class RawImage {
         // Ensure resample method is a string
         let resampleMethod = RESAMPLING_MAPPING[resample] ?? resample;
 
+        // Calculate width / height to maintain aspect ratio, in the event that
+        // the user passed a null value in.
+        // This allows users to pass in something like `resize(320, null)` to
+        // resize to 320 width, but maintain aspect ratio.
+        const nullish_width = isNullishDimension(width);
+        const nullish_height = isNullishDimension(height);
+        if (nullish_width && nullish_height) {
+            return this;
+        } else if (nullish_width) {
+            width = (height / this.height) * this.width;
+        } else if (nullish_height) {
+            height = (width / this.width) * this.height;
+        }
+
         if (BROWSER_ENV) {
             // TODO use `resample` in browser environment
 
@@ -360,7 +375,7 @@ export class RawImage {
                 case 'nearest':
                 case 'bilinear':
                 case 'bicubic':
-                    // Perform resizing using affine transform. 
+                    // Perform resizing using affine transform.
                     // This matches how the python Pillow library does it.
                     img = img.affine([width / this.width, 0, 0, height / this.height], {
                         interpolator: resampleMethod
@@ -373,7 +388,7 @@ export class RawImage {
                     img = img.resize({
                         width, height,
                         fit: 'fill',
-                        kernel: 'lanczos3', // PIL Lanczos uses a kernel size of 3 
+                        kernel: 'lanczos3', // PIL Lanczos uses a kernel size of 3
                     });
                     break;
 
@@ -452,7 +467,7 @@ export class RawImage {
             // Create canvas object for this image
             const canvas = this.toCanvas();
 
-            // Create a new canvas of the desired size. This is needed since if the 
+            // Create a new canvas of the desired size. This is needed since if the
             // image is too small, we need to pad it with black pixels.
             const ctx = createCanvasFunction(crop_width, crop_height).getContext('2d');
 
@@ -500,7 +515,7 @@ export class RawImage {
             // Create canvas object for this image
             const canvas = this.toCanvas();
 
-            // Create a new canvas of the desired size. This is needed since if the 
+            // Create a new canvas of the desired size. This is needed since if the
             // image is too small, we need to pad it with black pixels.
             const ctx = createCanvasFunction(crop_width, crop_height).getContext('2d');
 

tests/utils/utils.test.js

@@ -1,5 +1,6 @@
 import { AutoProcessor, hamming, hanning, mel_filter_bank } from "../../src/transformers.js";
 import { getFile } from "../../src/utils/hub.js";
+import { RawImage } from "../../src/utils/image.js";
 
 import { MAX_TEST_EXECUTION_TIME } from "../init.js";
 import { compare } from "../test_utils.js";
@@ -59,4 +60,35 @@ describe("Utilities", () => {
       expect(await data.text()).toBe("Hello, world!");
     });
   });
+
+  describe("Image utilities", () => {
+    let image;
+    beforeAll(async () => {
+      image = await RawImage.fromURL("https://picsum.photos/300/200");
+    });
+
+    it("Read image from URL", async () => {
+      expect(image.width).toBe(300);
+      expect(image.height).toBe(200);
+      expect(image.channels).toBe(3);
+    });
+
+    it("Can resize image", async () => {
+      const resized = await image.resize(150, 100);
+      expect(resized.width).toBe(150);
+      expect(resized.height).toBe(100);
+    });
+
+    it("Can resize with aspect ratio", async () => {
+      const resized = await image.resize(150, null);
+      expect(resized.width).toBe(150);
+      expect(resized.height).toBe(100);
+    });
+
+    it("Returns original image if width and height are null", async () => {
+      const resized = await image.resize(null, null);
+      expect(resized.width).toBe(300);
+      expect(resized.height).toBe(200);
+    });
+  });
 });