Document Node.js image loading pattern to avoid imread() DOM error

[Copilot]

cv.imread() throws ReferenceError: document is not defined in Node.js because it requires browser DOM APIs to access canvas/image elements.

Changes

• README.md: Added "Loading Images" section documenting browser vs Node.js patterns
• test/imread-nodejs.test.ts: Tests validating the Node.js approach and demonstrating correct usage patterns

Node.js Usage

Use Jimp (or similar) with matFromImageData() instead of imread():

const { Jimp } = require("jimp");
const cv = await require("@techstark/opencv-js");

// Load image with Jimp
const jimpImage = await Jimp.read("image.png");

// Convert to Mat
const img = cv.matFromImageData(jimpImage.bitmap);

// Process and cleanup
const gray = new cv.Mat();
cv.cvtColor(img, gray, cv.COLOR_RGBA2GRAY);
img.delete();
gray.delete();

See test/imread-nodejs.test.ts for complete working examples.

Browser environments continue using cv.imread('canvasId') unchanged.

Original prompt

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This section details on the original issue you should resolve

<issue_title>imread() throws error "abort(ReferenceError: document is not defined). Build with -s ASSERTIONS=1 for more info."</issue_title>
<issue_description>Based upon the node commonjs example:

const { getOpenCv } = require("./opencv.js");

async function main() {
  const { cv } = await getOpenCv();
  console.log("OpenCV.js is ready!");
  console.log(cv.getBuildInformation());
  const inputImage = cv.imread("Lenna.png");
  console.log("imread, done");
}

main();

Output:

(build info, as expected)
(a very long block of obfuscated code)

abort(ReferenceError: document is not defined). Build with -s ASSERTIONS=1 for more info.
(Use node --trace-uncaught ... to show where the exception was thrown)

Node.js v22.18.0
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes imread() throws error "abort(ReferenceError: document is not defined). Build with -s ASSERTIONS=1 for more info." #103

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[ttt43ttt]

@copilot remove the examples/node-image-loading.js. show the usage in the unit test, which is in node.js environment.

[Copilot]

@copilot remove the examples/node-image-loading.js. show the usage in the unit test, which is in node.js environment.

Done in 76bd2f8. Removed the example file and updated README to reference the unit test instead.