Tfjs: tf.fromPixels() function throw an error under 0.11.1

[PengWang0316]

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TensorFlow.js version

0.11.1

Browser version

Chrome Version 66.0.3359.181

Describe the problem or feature request

After updated the Tensor Flow js to 0.11.1, the tf.fromPixels() function throw an error:
Uncaught (in promise) TypeError: Cannot read property 'drawImage' of null
at MathBackendWebGL.fromPixels (backend_webgl.js:181)
at Engine.fromPixels (engine.js:302)
at ArrayOps.fromPixels (array_ops.js:292)
at eval (operation.js:12)
at Tracking.tidy (tracking.js:39)
at Object.descriptor.value (operation.js:12)
at eval (Webcam.js:69)
at Object.Tracking.tidy (tracking.js:39)
at Webcam.capture (Webcam.js:66)
at eval (index.js:288)
The code is come from webcam-transfer-learning (Transfer Learning to play Pacman via the Webcam) and run perfectly under the version 0.10.0

Code to reproduce the bug / link to feature request

Html has this element:

JS code as below:
tf.fromPixels(document.getElementById('webcam'));

[PengWang0316]

Really exciting about this new version which can let me use Tensorflow js to my project with the new saving model feature. 👍

[creativesands]

I was running a project a couple days back with the previous version and that worked, but with the latest version (0.11.1) I'm having the same issue as @PengWang0316 [TypeError: Cannot read property 'drawImage' of null]

[ghost]

Same as @PengWang0316 and @creativesands, very excited to save my model but unfortunately tf.fromPixel throws an error with the new version

[yellowmouse90]

I resolve using ImageData type.
FromPixel throw error from HTMLVideoElement, HTMLImageElement and HTMLCanvasElement but it works with ImageData

[nsthorat]

@dsmilkov @caisq can you prioritize / delegate this? I am currently out of office.

[caisq]

@dsmilkov Any thoughts on possible causes of this bug? I'm not very familiar with tf.fromPixels().

[dsmilkov]

I can take a look today. It is possible that something changed in Chrome - will investigate and update this thread.

[dsmilkov]

Fix is ready in https://github.com/tensorflow/tfjs-core/pull/1064