IPA IP 2021 Question 66
A question IPA Japan published in 令和3年度 ITパスポート試験 公開問題 問66, translated into English. ITPEC is based on the same exams.
When the gradation of each color of RGB is represented by a 3-digit binary number respectively, how many colors can be represented by color mixing?
Explanation
512 colors — 8 gradation levels for each of red, green and blue, combined independently.
- •One color with a 3-digit binary number: 23 = 8 levels, 000 to 111
- •Red, green and blue each take any of their 8 levels independently, so the mixtures number 8 × 8 × 8 = 512
Equivalently, a pixel uses 3 × 3 = 9 bits in all, and 29 = 512.
Answer (d)
Why not others:
- •(a) 8 — the number of levels of one color only, not of the mixtures
- •(b) 24 — multiplies 8 levels by 3 colors, adding the colors' choices instead of combining them
- •(c) 256 — 28, the count for 8 bits per pixel; three colors of 3 bits each make 9 bits, and twice as many colors
Key rule: The number of colors is the product of each component's levels, so it equals 2 raised to the total number of bits per pixel.
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This question comes from the past questions IPA Japan publishes, translated into English by ITPEC Practice. ITPEC Practice is an independent study tool and is not affiliated with IPA or ITPEC. See the original paper (PDF) or Report an issue.