問84
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スキャナやプリンタの性能の一つである解像度を表す単位はどれか。
平成24年度 春期 ITパスポート試験 問84
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This question's explanation and your answers so far.
解説
問 84
Incorrectア
bps stands for bits per second, and it is the unit of communication speed (transmission speed) that expresses how many bits of data can be sent in one second. It is used to indicate the speed of LANs, Internet lines, serial communication and so on, and it is written with prefixes such as Mbps (1 million bps) or Gbps (1 billion bps). It is an amount of data per unit of time, not a density of dots per unit of length, so it cannot be a unit of resolution.
- イ
正解 The correct answer is イ, dpi. dpi stands for dots per inch, and it is the unit that expresses how many dots can be placed within one inch (about 2.54 cm) of length. A scanner reads the original document as a collection of tiny dots, and a printer prints by arranging tiny dots, so this number of dots per inch directly indicates how fine the image is, that is, the resolution. The larger the value, the finer and more densely the dots are arranged, so the outlines of characters and the gradations of photographs are reproduced more smoothly. For example, a 600 dpi printer can place 600 dots per inch, so it is twice as fine as a 300 dpi model both vertically and horizontally, and per unit of area it can express four times as many dots. Because dpi is a density per unit of length, even for an image with the same number of pixels, lowering the dpi makes the printed size larger and coarser, while raising the dpi makes it smaller and more detailed. Therefore, the unit that represents the resolution of scanners and printers is イ.
Incorrectウ
fps stands for frames per second, and it is the unit of frame rate that expresses how many frames are displayed in one second in a video or animation. The larger the value, the smoother the motion looks. This is an indicator of fineness along the time axis, and it is a different characteristic from resolution, which shows how detailed each individual image is, so it is wrong.
Incorrectエ
Hz (hertz) is the unit of frequency that expresses how many vibrations or repetitions occur in one second. It is used for the clock frequency of a CPU (such as 3.5 GHz), the refresh rate of a display (such as 60 Hz), the AC frequency of a power supply and so on. This too is a count per unit of time rather than a spatial density of dots, so it is not suitable as the unit that represents the resolution of scanners and printers.
ここがポイント
- The unit of resolution, dpi — dots per inch, the number of dots in one inch, expresses how fine an image is. It is the resolution indicator for scanners and printers, and the larger the value, the more detailed the output. For the pixel density of displays and digital cameras, ppi (pixels per inch) is sometimes used instead, but the idea is the same: how many fit into one inch.
- Tell confusable units apart by asking how many of what per what — dpi is dots per unit of length (one inch), bps is bits per unit of time (one second), which is communication speed, fps is frames per unit of time, which is the smoothness of video, and Hz is repetitions per unit of time, which is frequency. By checking whether the denominator is a length or a time, you can tell that dpi is the only unit of resolution.
用語