How To: Green Screen for Schools

October 27, 2010

Green Screen, also known as Blue Screen or Chroma Keying, is a technique in video whereby you film your subject in front of a green or blue background and remove the blue/green colour to reveal another image behind. Most people know it best from weather forecasts – the forecaster isn’t actually standing in front of a weather map at all. It is used heavily in films and television programs too – see this link for an amazing video showing the potential of the technique.

How we’ve used it:

Students found it very motivating to use the green screen, as they could transport themselves anywhere they needed, for example play football at Bramall Lane, or play the guitar on stage at Wembley. We have found it particularly good for the students from the special schools we work with, as they can act out certain behaviours in a safe setting – for example crossing a road for a Green Cross Code video.

The Background

At the CLC we use a green screen (we decided on green as less people wear green than blue – anything the same colour as the background will also become transparent!) made up of a large green curtain on a curtain rail. You get best results with a very bright, vibrant green or blue colour, for example:

We also bought a Lastolite portable green screen with frame, which packs up small enough to take into schools. However, you don’t have to use a piece of cloth, it could be a wall painted blue or green with enough room for filming in front.

The Lighting and Other Considerations

You get the best results from an evenly lit background, as any difference in shade of colour will cause problems in the editing stage. If possible light the background and the subject separately, as this helps with crisp edges (and reduces the green halo effect). Try and avoid the subject casting shadows on the screen. Finally it is difficult to get a good result when there is a lot of movement; static scenes (e.g. news reports) work best.

The Editing

We use Adobe Premiere Pro to edit our green screen videos, but this is an expensive option for schools. There is a cheaper version, Adobe Premiere Elements, which costs around £60 for a single licence, and this still gives a good result:

  1. Drag your background image onto Video 1 track on timeline.
  2. Drag your green screen clip onto Video 2 track (i.e. above the background).
  3. Click on the Edit tab on the right and then Effects. Scroll down to find the Keying section and drag the Chroma Key effect to the green screen clip. (There is a specific Green Screen effect too, but the Chroma Key one is easier to tweak to get best result).
  4. Click on Edit Effect and open the Chroma Key effect (click on triangle).
  5. Click on the eyedropper icon then click on the preview screen to pick the most representative colour of the background (i.e. not too dark or light a shade).
  6. Use the Similarity and Blend sliders to get rid of any remaining background colour. I generally aim for Similarity between 15-30%, and Blend <20%.
  7. If there is a problem area in a corner (which never appears behind the subject), use the Eight-Point Garbage Matte effect. You can drag any of the 8 points to mask out areas you don’t want.

See below for a screen shot of Adobe Premiere Elements:

  • If you have access to a Mac, then iMovie has a Green Screen function:
    1. Click on iMovie > Preferences in the top menu bar, and tick the box next to Show Advanced Tools.
    2. Drag your background image or video onto the project area first.
    3. Now drag your green screen clip on top of the background image. In the menu that appears, choose Green Screen.
    4. The software does all the tricky stuff (like choosing the colour to remove) and gives a surprisingly good result.

    It is possible to chroma key video in Windows Movie Maker – see how to do it here. However the end result isn’t great unless you have a very well lit background, without too much variation in colour.

    Here is an example of  a music video, created using the Green Screen by year 6 pupils:


    French Summer School 2010

    September 1, 2010

    Following on from the success of our Spanish Summer School last year, we ran a French one for 3 days in August, aimed at Year 5 and 6 students with no or little prior knowledge of the language – although there were a few who had already learnt much of what we covered.

    Day 1

    We covered Greetings, How you are and Names in the morning. Each pair of attendees had the use of an iPad, which we used initially as an expensive mini-whiteboard using the free app Doodle Buddy, to write answers on. Having used mini-whiteboards as a teacher, it soon became clear that the iPads have the advantage of being much cleaner and avoiding the problem of pens running out of ink all the time.

    At the end of the morning, students then created a comic strip using all the language learnt, using the Strip Designer app on the iPad (which we called Pow! due to the icon used). This costs £1.79 but is worth it, as creating comic strips is really easy to do, using images from My Photos. The students used aliens for the characters in their strip, created using the Martian app. This is another free app to create your own alien, choosing colour, body shape, number of legs etc (ideal for teaching body parts!)

    You can then take a screen shot of the finished martian (hold down the home and power button) which automatically goes into My Photos. I also used this app to create a unique lock screen for each iPad so the students knew which was theirs for the week.

    Once these had been finished the attendees recorded a short piece of French on mp3 recorders to add to a Voki, using French names picked from a list rather than their own. Some of them used Audacity to edit their voice. Unfortunately I’ve not managed to embed the results here.

    After lunch we looked at some French-speaking countries and how to say where you lived. Everyone then used Animoto to create a short slideshow about a country.

    Cameroon culture

    Canada

    Unfortunately this was quite a frustrating day with regard to the technology, as our broadband connection was running very slowly and some Vokis were lost when the website froze. Other computers wouldn’t connect to the network or kept crashing, and by the end of the day I remembered why a lot of teachers don’t use computers in the classroom. Still it was worth it in the end.

    Day 2

    In the morning we did colours and because some students had already learnt them I did a bit on adjectival agreement too, in order for them to create a poster using the Moodboard Lite app (free) with French sentences describing images found on the internet. The Moodboard app was created for designers, artists etc but I liked it for the colours posters because one of the features was the ability to create a colour palette. The students used the Collins French dictionary app to look up any words they didn’t know. This was the £5.99 version, and although there was a cheaper one, this had a good balance of detail in the entries whilst still being simple enough for learners of this age.
    I’ve always noticed that children find it difficult to use a dictionary properly for a foreign language and so I spent a little time talking them through the process and explaining what some of the abbreviations meant. The novelty of the iPads certainly seemed to motivate them more than using a paper version.

    The rest of the morning was spent learning numbers 1-20, and we used the noughts and crosses background in Doodle Buddy to play bingo. Each child then planned a short stop-motion animation using some of the language learnt so far, using plasticine for characters and I Can Animate software.

    Day 3

    The students spent the morning editing their animations using Windows Movie Maker, adding voiceovers and titles.

    We then covered some basic weather vocabulary with the aim of creating weather forecasts in front of the green screen. Unfortunately we were running out of time so I gave the attendees the choice of how to create their weather-based presentations – using Voki, Animoto, Strip Designer, or filming it and editing in Windows Movie Maker. The groups that filmed their weather forecast used the free app iPrompt Pro as a scrolling script to read from on the iPads. It is a little complicated to use, as you have to fiddle with the settings to get the script to scroll slowly enough, but worth it to avoid the children clutching a bits of paper, and typing in the script reinforced the language.

    All of the work created over the 3 days was eventually uploaded to our French Summer School blog, which was set up using Posterous. I still really like this platform as it is so simple to use, and presents the work really nicely (for example multiple photos get put into a gallery).

    In all it was a very successful 3 days. I was really pleased with how well the iPads worked aspart of the classroom-type activities. Originally I had seen them very much as something students would use for reference and for passive skills (i.e. reading/listening), but there are enough free/cheap apps out there for creating work too, although we didn’t do any audio recording directly on the iPads. I shall try to do a separate post detailing all of the useful apps I found for MFL work.

    One last issue presented itself with the iPads, and that was transferring all of the images of the work the students did onto my computer. The photos don’t get synched through iTunes, but when you plug the iPad in, the PC sees it as a camera, and if you double click on the icon that appears in My Computer you can see all of the photos saved on the device and transfer them as you wish.

    You can hear me talk about the French and last year’s Spanish summer school in a podcast published on Joe Dale’s Integrating ICT into the Modern Languages Classroom blog.


    Chocolate Glogs from Totley Primary

    May 20, 2009

    Totley PrimaryA Year 4 class from Totley Primary visited the CLC yesterday to present the information they had learnt about Chocolate. Initially their teacher had asked to use Publisher to create leaflets, but after seeing the possiblities that Glogster offered, she decided that chocolate glogs were a better, and more varied, way to present the information.

    Before they arrived, the class took photos of their trip to a chocolate factory and their classroom display about the subject. They also borrowed some of our Flip Mino video cameras to record short interviews about their likes and dislikes, as well as jingles for made up chocolate bars.

    The teacher had created an educational account on Glogster, with accounts Chocolate Glogfor all the students. This meant that the Glogs remained private except to other members of the class. Each pupil created their own Glog, using text, images and video about Chocolate. They could customise the look of their Glog to suit their own personal taste, which they really liked. There is always a danger that pupils spend more time on the aesthetics than the content, but with close monitoring from the teacher, this shouldn’t be a problem.

    The finished posters were excellent, and the pupils remained focussed all morning on the task. For the last half hour of the session they were allowed to use the inbuilt messaging application, to talk to their friends. This is an excellent way of providing feedback, both between the pupils, and from the teacher. It is also an opportunity to discuss how to behave online towards others.

    The class teacher, Nicola Wileman, gave us some audio feedback. Please click here to hear it.