Raster dataラスターデータ divides an image into a grid of pixels arranged in rows and columns and records a color value for each pixel.
Divide the image into a pixel grid
Record a color value per pixel
Enlarged, outlines turn jagged
When shown large, each pixel simply stretches, and the edges of diagonal lines look jagged.
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More pixels (higher resolution) give finer detail, but there are more values to store, so the data grows larger. When the image is enlarged, each pixel stretches and the edges of diagonal lines and curves show stair-step jaggies. Raster data suits images like photographs, where color and shading change finely from spot to spot.
AnalogyIt is like a mosaic made of small colored tiles. From a distance you see a picture, but up close you can see the seams between each tile.
How to rememberThe word raster comes from the Latin for rake. Picture the parallel lines a rake leaves, packed side by side, as rows of pixels stacked one on another.
Exam points
ExamRaster dataラスターデータ holds color and brightness values for every pixel, so it can be edited by changing colors one pixel at a time.
Bitmap dataビットマップデータ is image data that records each pixel's color as a sequence of bits, and the term means almost the same as raster data.
The more bits assigned to each pixel, the more colors it can show: black and white need just 1 bit, while full color with about 16.77 million colors needs 24 bits. The BMP format is a typical file format that saves images this way.
AnalogyIt is like a sheet of graph paper with a color number written in each square. Read the numbers in order and you can paint the original picture again.
How to rememberRemember it literally: bits laid out to match positions on the screen, like a map.
Exam points
ExamWithout compression, the size of bitmap dataビットマップデータ is set by pixel count × bits per pixel. With the same bits per pixel, doubling both the width and height in pixels makes the size four times larger.
Mix-upBitmap dataビットマップデータ and raster dataラスターデータ both represent images as a pixel grid; they differ only in name and refer to nearly the same thing.
Vector dataベクターデータ represents an image with point coordinates and shape information such as the lines and curves that connect them and the fills inside them.
Record coordinates and shape data
Calculate for the display size
Draw smooth outlines
Since it is drawn from the results every time, the edges stay smooth even when enlarged.
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Because it is redrawn from coordinates and formulas every time it is shown, its outlines never blur or turn jagged when scaled up or down. Its size depends not on the on-screen dimensions but on the number and complexity of shapes, so logos and drawings built from simple shapes stay small. On the other hand, it is a poor fit for images like photographs, where the color changes from point to point.
AnalogyIt is like handing over drawing instructions such as “draw a line from this point to that one,” rather than a finished picture. Follow the steps and you can draw it cleanly on paper of any size.
How to rememberVector is the same word as the math term for a quantity with direction. Picture an arrow running from a start point to an end point to draw a line.
Exam points
Mix-upHow edges look when enlarged depends on how the image is stored. Vector dataベクターデータ is redrawn from formulas and stays smooth, while pixel-based raster dataラスターデータ stretches its pixels and its edges turn jagged.