Christian Heilmann

Flipping the image when accessing the laptop camera with getUserMedia

Friday, July 19th, 2013 at 9:22 pm

This is one of my bugbears: when I see demos or tools that access the camera with getUserMedia and the image is “the wrong way around”. Say I sit in front of this computer, and lean slightly to my left. If you just use getUserMedia and connect the stream to a video element, this is what you get:

wrong

That’s not right, I would expect the video to look like this:

right-way

This is very simple to achieve. First of all, you need to flip the video element with CSS:

video {
  -webkit-transform: scaleX(-1);
  transform: scaleX(-1);
}

Of course, this is not enough, as the CSS transformation doesn’t change the pixels of the video. In order to flip the video pixels around when you access them with CANVAS – for example to add filter effects or generate animated GIFs you also need to transform the context:

  // ctx is the plotting canvas' context
  // w is the width of the canvas
  ctx.translate(w, 0);
  ctx.scale(-1, 1);

Doing this, makes me happy. Please do this.

Share on Mastodon (needs instance)

Share on Twitter

Newsletter

Check out the Dev Digest Newsletter I write every week for WeAreDevelopers. Latest issues:

160: Graphs and RAGs explained and VS Code extension hacks Graphs and RAG explained, how AI is reshaping UI and work, how to efficiently use Cursor, VS Code extensions security issues.
159: AI pipelines, 10x faster TypeScript, How to interview How to use LLMs to help you write code and how much electricity does that use? Is your API secure? 10x faster TypeScript thanks to Go!
158: 🕹️ Super Mario AI 🔑 API keys in LLMs 🤙🏾 Vibe Coding Why is AI playing Super Mario? How is hallucinating the least of our worries and what are rules for developing Safety Critical Code?
157: CUDA in Python, Gemini Code Assist and back-dooring LLMs We met with a CUDA expert from NVIDIA about the future of hardware, we look at how AI fails and how to play pong on 140 browser tabs.
156: Enterprise dead, all about Bluesky and React moves on! Learn about Bluesky as a platform, how to build a React App and how to speed up SQL. And play an impossible game in the browser.

My other work: