Tell additive color mixing, which makes colors with light, apart from subtractive color mixing, which makes colors with ink, by their primary colors and what mixing them produces.
Distinguish dpi from ppi by what they count (dots or pixels) and where each is used, and work out a pixel count from a resolution.
Explain what CG stands for and what kind of technology it refers to.
Additive color mixing (加法混色) creates colors by overlapping the three primary colors of light, red (R), green (G) and blue (B), and gets brighter the more colors are added.
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Because light itself is being added together, each extra color increases the amount of light reaching the eye. Overlapping all three at equal, full strength gives white. Devices that show colors by giving off light, such as displays and projectors, work this way.
AnalogyIt is like adding flashlights one by one in a dark room: the wall they light up keeps getting brighter.
How to rememberLook at a screen through a magnifying glass and you can see rows of tiny red, green and blue dots.
Exam points
ExamThe three primary colors of light (光の三原色) are red, green and blue (RGB).
ExamIn additive color mixing (加法混色), overlapping red, green and blue at equal strength produces white.
Subtractive color mixing (減法混色) creates colors by overlapping the three primary colors of ink, cyan (C), magenta (M) and yellow (Y), and gets darker the more colors are added.
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Ink absorbs part of the light that hits it, so the more colors are layered, the less light is reflected back to the eye. In theory, layering all three gives black. Real inks alone produce a muddy black, so printers and printing presses add black ink (K) and work with the four colors of CMYK.
AnalogyIt is like stacking sheets of colored cellophane one at a time: what you see through them grows steadily darker.
How to rememberThe K in CMYK is said to come from "Key plate", the printing plate that lays down the black.
Exam points
ExamIn subtractive color mixing (減法混色), layering the three colors cyan, magenta and yellow gives black in theory.
Mix-upLayering RGB and getting brighter is additive color mixing (加法混色); layering CMY and getting darker is subtractive color mixing (減法混色).
dpi (dots per inch) is a unit of resolution expressed as the number of dots lined up across one inch (about 2.54 cm).
Resolution
Pixels from scanning 4 in × 5 in (width × height)
Pixel count
150 dpi
600 × 750
450,000
300 dpi
1,200 × 1,500
1,800,000 (4 times 150 dpi)
600 dpi
2,400 × 3,000
7,200,000 (16 times 150 dpi)
The larger the value, the more finely the dots are packed, allowing more detailed scanning and printing. On an image scanner each dot read becomes one pixel of the image, so each side yields "length (inches) × dpi" pixels. Since the pixel count is width times height, doubling the dpi makes it four times as large.
AnalogyIt is like graph paper of the same size: the finer the grid, the smoother the picture you can draw on it.
How to rememberOne inch is roughly the width of an adult's thumb.
Exam points
Examdpi is the unit for how finely an image scanner (イメージスキャナ) reads an image and how finely a printer places its dots.
ExamThe data size of an uncompressed image is the vertical pixel count (画素数) × the horizontal pixel count × the data size of one pixel.
ppi (pixels per inch) is a unit of resolution expressed as the number of pixels lined up across one inch.
A pixel is the smallest unit that makes up a digital image, and ppi is mainly used to describe how fine a display or smartphone screen is. Even on screens of the same size, a higher ppi makes the outlines of text and photos look smoother.
AnalogyIt is like tiling a wall of fixed size: the smaller the tiles and the more of them you use, the finer the pattern they can form.
Exam points
Mix-updpi counts dots per inch, while ppi counts pixels (画素) per inch. For both, a larger value means finer detail.
CG is the short name for the technology of using a computer to create or edit images and video.
There is 2D CG, which draws flat shapes and pictures, and 3D CG, which uses calculation to render solid objects with depth. It is used across many fields, from game and film imagery to previews of finished products and buildings.
How to rememberAn abbreviation formed from the initials of the two words Computer Graphics.
Exam points
ExamProjecting CG imagery onto the surface of a building or other solid object to create a visual effect is called projection mapping (プロジェクションマッピング).
Additive color mixing layers RGB, the three primary colors of light, and gives white when all three are overlapped at equal strength.
Subtractive color mixing layers CMY, the three primary colors of ink, and gives black in theory when all three are overlapped. Printing uses CMYK, which adds black ink.
dpi is the resolution unit for image scanners and printers; since each dot read becomes one pixel, the pixel count along each side of the image is "length (inches) × dpi".
CG (computer graphics) is the technology of creating images and video with a computer.