Chapter 35 — Quiz

Twenty-five questions to check your command of compositing, keying, stock elements, and the ethics of synthetic media. Mix of multiple choice, true/false (with justification), short answer, and "what's wrong with this shot?" Answers and a review map are at the end — attempt all twenty-five before you check.

Multiple choice

1. The alpha channel of a composited layer stores: - (a) the red, green, and blue color of each pixel - (b) the transparency (opacity) of each pixel - (c) the brightness of each pixel only - (d) the motion of each pixel between frames

2. In a matte (the alpha viewed in black-and-white), a grey pixel means: - (a) an error in the key - (b) fully opaque — keep the foreground - (c) fully transparent — show the background - (d) partial transparency — a soft or semi-transparent edge

3. Green is the default chroma-key color mainly because: - (a) it is the brightest color a camera can record - (b) it is far from skin tones, sensors resolve green best, and it needs less light than blue - (c) editing software can only key green - (d) green backgrounds are cheaper than blue ones

4. The single most important reason to put 6–10 feet between your subject and the green screen is to: - (a) make the shot look more cinematic - (b) reduce green spill on the subject and drop the subject's shadow off the screen - (c) fit more people in frame - (d) increase the depth of field

5. When lighting a green-screen shot, the subject should be lit: - (a) exactly the same as the screen - (b) as brightly as possible to overpower the green - (c) to match the background plate they'll be composited into - (d) with no light — the key handles it

6. Despill refers to: - (a) removing green light that contaminated the subject's edges - (b) making the green screen brighter - (c) spilling the background color onto the foreground on purpose - (d) cleaning coffee off the color-grading desk

7. A chroma keyer and a color qualifier (Chapter 32) are fundamentally the same tool because both: - (a) change the frame rate - (b) isolate a range of hue/saturation/luma — one feeds a grade, the other feeds transparency - (c) only work on skin tones - (d) require a green screen

8. You shoot a clip knowing it will be keyed. The best capture choice is: - (a) the smallest file size possible - (b) the least-compressed, highest-chroma format available (4:2:2 over 4:2:0) - (c) a heavily compressed 4:2:0 clip to save card space - (d) it makes no difference; keying happens in post

9. Rotoscoping is: - (a) automatically keying a green screen - (b) drawing a mask and animating it frame-by-frame to follow a moving subject - (c) a type of camera move - (d) a stock-footage library

10. Light-on-black stock elements (fire, flares, light leaks) are usually composited with which blend mode, so the black disappears? - (a) multiply - (b) normal/over - (c) screen (or add) - (d) difference

11. A screen replacement is commonly needed because a real filmed screen: - (a) is always the wrong aspect ratio - (b) flickers/bands (rolling shutter), shows moiré, is too dim, glares — or the final UI wasn't ready on set - (c) cannot be focused on - (d) records no sound

12. The technique that locks a replacement image to the four corners of a moving screen is: - (a) a garbage matte - (b) a corner-pin (planar) track - (c) a light wrap - (d) chroma subsampling

13. According to §35.6, the question that gates whether you may create synthetic media of a real person is: - (a) disclosure - (b) whether it looks convincing - (c) informed, specific consent - (d) whether it's for fiction or nonfiction

14. Disclosure of synthetic media is absolutely required in: - (a) obvious fiction (a monster, a set extension) - (b) documentary and journalism, where it could be mistaken for real - (c) never — disclosure is always optional - (d) only when required by a specific named law

15. A clean plate is: - (a) a freshly formatted memory card - (b) an extra shot of the empty location with the to-be-removed object gone, used as a patch - (c) a green screen with no wrinkles - (d) a fully corrected, neutral grade

16a. A light wrap in a composite is there to: - (a) brighten the whole background - (b) let a thin band of the background's light bleed onto the foreground's edges, so it sits in the scene - (c) remove green spill - (d) sharpen the matte edge

16b. A garbage matte is used to: - (a) delete the whole background automatically - (b) roughly crop out non-green junk (stands, cloth edges) before the keyer runs - (c) add grain to a composite - (d) replace a screen

16c. Compared with a moving camera, a locked-off camera makes a composite: - (a) harder, because there's less motion blur to hide edges - (b) easier, because nothing has to be motion-tracked - (c) impossible to grade - (d) no different at all

True / False — justify your answer in one sentence

16. Green screen is primarily a post-production effect; the shoot barely matters.

17. A composite can look fake even when the matte edge is technically perfect.

18. Overexposing the green screen makes it easier to key.

19. A keyer should be judged first in color, over the final background.

20. A stock element that is sharper and cleaner than the footage around it is a problem, not a bonus.

21. Having a signed release from a person means any synthetic use of their likeness is automatically ethical.

Short answer

22. Name the two separate lighting jobs on a green-screen shoot and, in a phrase each, why they're separate.

23. List the five-step order for pulling and cleaning a key.

24. State the chapter's one-line premise about where a clean composite is really made — and give one on-set reason and one capture reason it's true.

What's wrong with this shot?

25. A branded video composites a spokesperson (shot on green) into a warm, window-lit studio. In the final shot: the spokesperson has a faint green rim on their hair; their key light is hard and comes from the right, while the studio's window light is soft and clearly comes from the left; the subject looks razor-sharp and slightly "cut-out" against the softer background; and the whole thing hasn't been graded together. Name at least four distinct problems and the fix for each.

Answer Key

Answers and explanations **1. (b)** — Alpha = per-pixel transparency; R/G/B store color. **2. (d)** — Grey = partial transparency (soft/semi-transparent edges: hair, motion blur, glass). White = keep, black = drop. **3. (b)** — Far from skin tones, best-resolved channel (twice the green photosites in a Bayer array), and needs less light than blue. **4. (b)** — Distance kills spill and drops the subject's shadow off the screen — the two biggest on-set key wreckers. **5. (c)** — The subject is lit for the *plate* they'll land in, not for the screen. Matching light is what makes a composite believable. **6. (a)** — Despill removes green light contaminating the subject's edges; the loudest "green screen!" tell if left in. **7. (b)** — Both isolate a hue/sat/luma range; a qualifier feeds it to a grade, a keyer feeds it to alpha/transparency. **8. (b)** — Chroma subsampling matters: 4:2:2 keeps more color detail than 4:2:0, so color edges key far cleaner. You can't add back what the codec discarded. **9. (b)** — Roto = a hand-drawn mask animated over time to follow motion when you can't key; green screen exists to avoid it. **10. (c)** — Screen/add mode makes black transparent, letting only the bright element through — no matte needed. **11. (b)** — Real screens flicker/band (rolling shutter), moiré, run dim, glare, or the UI wasn't final on the day. **12. (b)** — A corner-pin/planar track pins the new layer to the screen's four corners frame-by-frame. **13. (c)** — Consent gates whether you *may*. No informed, specific consent → stop. **14. (b)** — In documentary/journalism the duty not to deceive is absolute; obvious fiction needs no disclaimer. **15. (b)** — A clean plate is an empty-frame shot used as a perfect, already-matched patch for removals. **16a. (b)** — A light wrap bleeds a little of the background's light/color onto the foreground edge so it sits *in* the scene rather than on top of it. **16b. (b)** — A garbage matte roughly masks out non-green junk (stands, cloth edges) before the keyer, so the keyer only deals with actual green. **16c. (b)** — Locked-off = nothing to motion-track; the composite is far easier. Moving cameras require tracking the foreground and background together. **16. False** — A clean key is *lit and shot*; the shoot (even screen, separation, matched subject light, good codec) determines whether the post key is easy or impossible. **17. True** — Mismatched light, lens/DoF, camera angle, motion, grade, or grain read as "fake" even with a flawless edge; the eye reads light before edges. **18. False** — A blown, uneven screen keys *worse*. Expose it to a clean, even mid-green. **19. False** — Judge the *matte in black-and-white* first (the truth of your transparency); check in color over the real background only after cleaning. **20. True** — Mismatch is the amateur tell; the element must share the shot's grain, sharpness, motion blur, grade, and light direction. **21. False** — Consent settles whether you *may*; it doesn't settle *deception*. A convincing impersonation that could mislead still requires disclosure (and some uses remain wrong regardless). **22.** (1) Light the *screen* — flat, even, one green value, so the keyer has one color to find. (2) Light the *subject* — matched to the background plate, so they belong in the new world. Separate because they serve opposite goals and their lights must not contaminate each other. **23.** Pull the key (sample green → matte) → read the matte in black-and-white → despill → clean the matte (clip black, clip white, shrink/soften — gently) → garbage-matte and composite/grade together. **24.** Premise: *a clean composite is lit and shot, not fixed in post.* On-set reason: an even, wrinkle-free screen with subject separation and matched light gives an easy, clean matte. Capture reason: a least-compressed, high-chroma format (4:2:2, higher bit depth) gives clean color edges — detail you can't recover later. **25.** (1) *Green rim on hair* → despill in post; on set, add a rim light and more separation. (2) *Light direction/quality mismatch* (hard right key vs. soft left window) → re-light the subject to match the plate (soft, from the left); if stuck in post, relight with grading windows and flip/soften as far as possible, but this is really an on-set fix. (3) *Razor-sharp "cut-out" subject over a soft background* → soften the matte edge slightly, add a light wrap, and match depth of field/focus to the plate. (4) *Not graded together* → grade foreground and background to one shared look, contrast, and color temperature; match grain; keep skin on the flesh-tone line (Chapter 32).

Topics to review by question

  • Q1–2, 17: the alpha channel and the matte — §35.1
  • Q3–5, 16, 18, 22: green screen, spill, two lighting jobs, separation — §35.2
  • Q6–8, 19, 23: keying, despill, matte cleanup, capture format — §35.3
  • Q9, 15, 16b: masks, roto, garbage matte, clean plates — §35.4
  • Q16a, 16c: light wrap, locked-off composites — §35.1, §35.3
  • Q10–12, 20: stock elements, blend modes, screen replacement, matching — §35.5
  • Q13–14, 21: consent, impersonation, disclosure — §35.6
  • Q24: the chapter premise (finish begins on set) — §35.1–35.3
  • Q25: integrated composite diagnosis — §§35.1–35.3 + Chapter 32