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2 What do these things have in common?

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8 Blue/green screen compositing

9 Process (overview) Filming of a subject in front of an evenly lit, bright, pure blue (or green) background The compositing process, whether photo- chemical or digital, replaces all the blue in the picture with another image, known as the background plate

10 How does it work? Imagine a photo:

11 Select a colour or similar range of colours by the magic wand tool

12 Delete the selected areas

13 After doing this, overlay the image over something else Now imagine same process for every single frame of a video clip  chroma keying

14 The filming process Traditional method: Film subject over homogenous green background Make sure subject does not wear any green clothing. Why? –Will disappear when chroma key is applied Subject must be drowned out with strong white light (from all directions). Why? –To eliminate shadows on green background

15 Traditional method Advantages –Relatively easier to adjust and fine-tune during filming Disadvantages –Background may not be homogenous green

16 New method Shine green light on a subject over a special background Advantages: –Homogeneity of background does not matter –Potential to produce very well done greenscreen effect Disadvantages: –Subject cannot wear reflective clothing / have reflective objects (eg. spectacles) as green light will be reflected –Subject cannot be too close to camera or green light will drown out the subject, no matter how strong the white light is –Takes a lot more adjustment of lighting

17 Setting up the background

18 Setting up green light (stick to camera)

19 Preparing to film

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21 Filming

22 Note the white lights all around to drown out the shadows

23 Examples of badly done greenscreen Shadow (will cause a green border to remain around character after chroma keying) - Not enough white light in some directions Non-homogenous / grainy background -Green light intensity too strong / not enough white light

24 Shadow (will cause a green border to remain around character after chroma keying) Different shades of green - Green light too focused / too close to subject

25 Green light reflected off surface of subject (will disappear in when chroma is applied) - Green light too close to subject / too strong / not enough white light on subject

26 Background has black streaks due to irregular surface - White light has not drowned out the scene (reposition the angles, increase intensity)

27 Example of well-done greenscreen

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29 In premiere… (after capturing the shot footage) Under effects tab  Video effects  Keying  Chroma key Drag to the clip you want to chroma key

30 Under effects control, expand the “chroma key” effect you just inserted Under the colour tab, click on the dropper tool and click on the background of the scene to change the keyed colour from white to the specific shade of green In this case, clip to be keyed is overlaid on a black video Adjusting colour of key

31 Work with the similarity tab This is what you will get when similarity is 0 (too low) Adjusting similarity

32 This is what you will get when similarity is too high

33 Find the optimum similarity (note the presence of green border even if green-screen is quite well done) Adjusting similarity

34 Find the optimum blend (here it’s 100%) White surfaces may be faded off, but that is alright if clip is overlaid over a non-moving, homogenous background Adjusting blend

35 Drag a “Color Balance (RGB)” effect to ABOVE the chroma key effect Color Balance (RGB) can be found under Video effects  Image control Decrease green and increase red and blue slightly until you get something like this Color balance

36 Drag a “Brightness and Contrast” effect to BELOW the chroma key effect Brightness and Contrast can be found under Video effects  Color Correction Adjust brightness and contrast until you get something like this Brightness & Contrast

37 Additional effects Additional effects you may want to use to finetune your chroma key: Lighting effects –Video effects  Adjust  Lighting Effects Gamma correction –Video effects  Image Control  Gamma Correction Color channels –Video effects  Color Correction  Channel Mixer OR Color Balance –note: this color balance is different from the color balance (RGB) A second chroma key

38 Words of caution Method to do the perfect chroma key varies with your footage Need to experiment with the above effects Play through the entire clip when you adjust the settings for the effects (may work for one frame but not for others) If necessary, cut the clip into a few clips and apply different effects for each To make post-production work easier, footage must be well-shot (refer to abovementioned examples of badly done and well done greenscreen)

39 Take test shots! Always take some test shots with the subject in the greenscreen room before the actual thing Note down where you place your camera and the lights (esp. the intensity of green lights, white lights and their angle) Try out different combinations but note down which is used for which shot on the tape Try out chroma keying on the computer and see which setup works best Do the optimum setup of the lights, etc on the actual shooting

40 Before each take, write down the arrangement of lights on a paper, put in front of the camera, and record for a few seconds  Allows editor to see which setup gave best effect in Premiere

41 So, how do I get the greenscreen room? Approach the art department (in the art office on third level of SRC) beforehand (ie. a few days) On the day itself, find the same teacher and ask for permission to get the keys Remember to keep the room clean, switch off all the lights, fans and air-cons after using, and lock up

42 The End. Good luck!