<p>Most likely, they are simply using an output of the notes with transparency.  If you output the digital version of the notes with a transparent background you could just layer it over the video once properly aligned and it would work fine.  </p>

<p>Alternately, a quicker process if they do not support alpha is to just apply a blend between the layers.  Since the background matches the video except for where the hand is, it would blend very smoothly.</p>

<p>Finally, what is known as a luma-key could also be used on the screen capture file to generate transparency anywhere that the luminosity (brightness) differs from the empty background.</p>

<p>Any of these options could be used and they are all extremely easy to use, though the first requires the most advanced technique to generate the alpha content, but would also produce the best results.</p>

CC BY-SA 3.0
2014-01-12T20:20:22.970Z
Thanks for the answer AJ. The part that I'm stuck on is removing the background from the raw video of the hand. In the tutorials, the background is pure white (and not the grey tablet with a screen that is being filmed). I'll keep looking.
Jack
CC BY-SA 3.0
2014-01-12T20:31:28.843Z
@Jack - removing the background from the video with the hand is the wrong way to do it.  You work from the digital version of the notes that knows exactly what is stuff they drew and what is background.  Then you layer those notes over the video from the actual camera, just the way it is, no alterations necessary.
AJ Henderson
CC BY-SA 3.0
2014-01-12T20:50:41.033Z
thanks. How would you get a pure white background though? By layering the notes over the hand video, you would see the grey finish of the tablet.
Jack
CC BY-SA 3.0
2014-01-12T20:54:05.503Z
@Jack - the easiest way is just to lower the white point so that grey becomes white.  If you notice the edge of the hand (at least in the video clip you linked) is a bit washed out on the brighter end.
AJ Henderson
CC BY-SA 3.0
2014-01-11T17:05:16.027Z
2014-01-11T17:05:16.027Z
AJ Henderson
<p>Udacity has answered your question here <a href="http://blog.udacity.com/2014/09/udacity-videos-transparent-hand.html" rel="nofollow">http://blog.udacity.com/2014/09/udacity-videos-transparent-hand.html</a></p>

CC BY-SA 3.0
2016-04-20T12:10:53.290Z
It's recommended to paraphrase the solution given at the link, so should the link go dead, future readers aren't left in the dark.
Gyan
CC BY-SA 3.0
2016-04-20T12:11:19.473Z
Sad but true: the ethos of StackExchange is that answers should be sufficiently complete as to be practical despite the death of external links.  A definitive external link could be a "see also" or "see for more details" but the actual answer needs to be present in the Answer.
Michael Tiemann
CC BY-SA 3.0
2016-04-21T14:49:52.190Z
Yeah, it would certainly be preferable to have more details from the link, though in this case, with such a direct answer, I'm not going to mark it as needing more detail.  It would be a super improvement to include some of the details, but you can't get a much better response than having the details straight from the source.
AJ Henderson
CC BY-SA 4.0
2018-08-23T10:13:31.120Z
What is not clear is what they meant by overhead camera, is it the camera of the tablet, if so how does it record the back of the hand, ie if it is a camera outside ie somewhere in the room or say on top of the teachers head then how do they synchronise the relative position of it with respect to the tablet.
ishandutta2007
CC BY-SA 3.0
2016-04-20T10:15:09.447Z
2016-04-20T10:15:09.447Z
abtom13
<p>What with the felt-tip pen and the transparency of the writing surface, this actually looks more like they're writing on a transparent whiteboard. Probably perspex, or plexiglass.</p>

<p>This type:
<img src="https://i.sstatic.net/JTALO.jpg" alt="Whiteboard"></p>

CC BY-SA 3.0
2014-01-12T20:18:19.117Z
Thanks for the answer Callum, from all of the information in the links above it seems that they are definitely creating the final video using a composition of two videos and some processing in post.
Jack
CC BY-SA 3.0
2014-01-12T02:16:19.707Z
2014-01-12T02:16:19.707Z
Cal McLean
<p>In a typical Udacity course, the hand written course videos are displayed with the writers hand beneath a semi-transparant view of the notes (1:02 in video linked below).</p>

<p>I want to replicate this to record some tutorial videos, but am stuck on how Udacity managed to achieve this effect.</p>

<p>Here is a video of their set up:
<a href="http://blog.udacity.com/2013/06/coffee-break-episode-6-inside-recording.html" rel="nofollow">http://blog.udacity.com/2013/06/coffee-break-episode-6-inside-recording.html</a></p>

<p>And here is some more information from one of the teachers:
<a href="https://medium.com/teaching-learning/1d7c77b857de" rel="nofollow">https://medium.com/teaching-learning/1d7c77b857de</a></p>

<p>From what I gather, they have a Tablet that they draw on, which they then use some form of screen capture software to record the video of the notes. </p>

<p>At the same time, they are recording a video of the teacher writing on the tablet.</p>

<p>With these two videos they seem to be chroma keying the screen capture out of the video of the teacher's hand.</p>

<p>How are they achieving this effect? If they are chroma keying the screen capture out of the teacher's hand video, how can this be achieved?</p>

<p>Thanks </p>

<video><chromakey>
Udacity - Hand under notes video effect
Jack
# Udacity - Hand under notes video effect

(Asked by: username_0 on 2014-01-11)

In a typical Udacity course, the hand written course videos are displayed with the writers hand beneath a semi-transparant view of the notes (1:02 in video linked below).

I want to replicate this to record some tutorial videos, but am stuck on how Udacity managed to achieve this effect.

Here is a video of their set up:
<http://blog.udacity.com/2013/06/coffee-break-episode-6-inside-recording.html>

And here is some more information from one of the teachers:
<https://medium.com/teaching-learning/1d7c77b857de>

From what I gather, they have a Tablet that they draw on, which they then use some form of screen capture software to record the video of the notes.

At the same time, they are recording a video of the teacher writing on the tablet.

With these two videos they seem to be chroma keying the screen capture out of the video of the teacher's hand.

How are they achieving this effect? If they are chroma keying the screen capture out of the teacher's hand video, how can this be achieved?

Thanks

**Tags:** video, chromakey


---

## 3 answers

### Answer by username_1 on 2014-01-11. Score: 3

Most likely, they are simply using an output of the notes with transparency. If you output the digital version of the notes with a transparent background you could just layer it over the video once properly aligned and it would work fine.

Alternately, a quicker process if they do not support alpha is to just apply a blend between the layers. Since the background matches the video except for where the hand is, it would blend very smoothly.

Finally, what is known as a luma-key could also be used on the screen capture file to generate transparency anywhere that the luminosity (brightness) differs from the empty background.

Any of these options could be used and they are all extremely easy to use, though the first requires the most advanced technique to generate the alpha content, but would also produce the best results.

> **Comments:**
> **username_0**: Thanks for the answer AJ. The part that I'm stuck on is removing the background from the raw video of the hand. In the tutorials, the background is pure white (and not the grey tablet with a screen that is being filmed). I'll keep looking.  
> **username_1**: @username_0 - removing the background from the video with the hand is the wrong way to do it.  You work from the digital version of the notes that knows exactly what is stuff they drew and what is background.  Then you layer those notes over the video from the actual camera, just the way it is, no alterations necessary.  
> **username_0**: thanks. How would you get a pure white background though? By layering the notes over the hand video, you would see the grey finish of the tablet.  
> **username_1**: @username_0 - the easiest way is just to lower the white point so that grey becomes white.  If you notice the edge of the hand (at least in the video clip you linked) is a bit washed out on the brighter end.  

---

### Answer by username_2 on 2016-04-20. Score: 1

Udacity has answered your question here <http://blog.udacity.com/2014/09/udacity-videos-transparent-hand.html>

> **Comments:**
> **username_3**: It's recommended to paraphrase the solution given at the link, so should the link go dead, future readers aren't left in the dark.  
> **username_4**: Sad but true: the ethos of StackExchange is that answers should be sufficiently complete as to be practical despite the death of external links.  A definitive external link could be a "see also" or "see for more details" but the actual answer needs to be present in the Answer.  
> **username_1**: Yeah, it would certainly be preferable to have more details from the link, though in this case, with such a direct answer, I'm not going to mark it as needing more detail.  It would be a super improvement to include some of the details, but you can't get a much better response than having the details straight from the source.  
> **username_5**: What is not clear is what they meant by overhead camera, is it the camera of the tablet, if so how does it record the back of the hand, ie if it is a camera outside ie somewhere in the room or say on top of the teachers head then how do they synchronise the relative position of it with respect to the tablet.  

---

### Answer by username_6 on 2014-01-12. Score: 1

What with the felt-tip pen and the transparency of the writing surface, this actually looks more like they're writing on a transparent whiteboard. Probably perspex, or plexiglass.

This type:
![Whiteboard](https://i.sstatic.net/JTALO.jpg)

> **Comments:**
> **username_0**: Thanks for the answer Callum, from all of the information in the links above it seems that they are definitely creating the final video using a composition of two videos and some processing in post.  

---

