The Vibrating Poster
A school notice-board poster must be 60 cm × 45 cm, painted in gouache, and read clearly from 5 m. The message is "Save Water". The candidate uses a pure red background and pure green letters in roughly equal areas, plus several bright blue water drops. From 3 m the letters appear to vibrate and are hard to read. The art teacher says the poster fails its function even though the colours are strong. The candidate has one afternoon to repaint and wants to keep a bold, festive look. Available paints include titanium white, lemon yellow, viridian, ultramarine, crimson, burnt sienna, and black.
1. Diagnose the problem using colour-contrast concepts, distinguishing hue, value, and area effects.
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The problem is not that red and green are 'bad colours'; it is uncontrolled contrast. Red and green are near-complements, so at full saturation and similar value they produce simultaneous contrast and afterimages, which makes edges vibrate. Equal areas intensify the effect because neither colour is clearly dominant. The bright blue drops add a third competing hue, further fragmenting attention.
Value is the critical readability factor: if the red and green are close in tone, the letter shapes lose their silhouette even though the hue contrast is strong. The candidate has confused chromatic contrast with legibility. A poster read at 5 m needs a clear value hierarchy and controlled area proportions, not maximum saturation everywhere.
2. Propose two revised schemes with specific proportions, and explain why each improves readability.
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Scheme A - controlled complement. Deep crimson background (about 70%), off-white letters (20%), dark green shadow/outline and small green accents (10%). The complement is retained, but the large red area dominates and the letters gain a strong light-dark edge. The green is no longer equal in area or saturation, so vibration is reduced.
Scheme B - analogous cool with one warm accent. Viridian/ultramarine background (70%), dark ultramarine letters (20%), white water drops (10%), plus a small burnt-sienna accent. This removes the complementary vibration while keeping a festive, bold look.
In both schemes, the letter forms are separated from the background by at least three value steps on a grey scale. Hue contrast supports the message; value contrast carries legibility at 5 m.
3. How should the candidate test the revised poster before final painting?
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Test in this order:
- Squint test: Squint at a small colour rough. If the lettering disappears, value contrast is too weak.
- Greyscale copy: Photocopy or photograph the rough in greyscale. The text should remain clearly readable.
- Distance test: Place the rough at 5 m and check readability, then at 3 m to confirm the vibration is gone.
- Colour-vision check: Since red/green is a common confusion pair, ensure the message also reads in a red-green simulation or rely on value and shape rather than hue alone.
Only after these tests should the candidate commit to the final 60 × 45 cm painting.