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Section 18.2 Understanding Image Representation
Understanding images requires understanding a set of abstractions:
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Images are made up of little pixels (objects of the Pixel class), laid out on an (x,y) grid.
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Each pixel contains a red value, a green value, and a blue value.
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Each color value is actually a number between 0 and 255.
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If a pixel has red=0, green=0, and blue=0 then the color is black since this is an absence of any color of light.
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If a pixel as red=255, green=255, and blue=255 then the color is white. Try tilting the bottom of a cd in white light to see the colors in the light.
Figure 18.2.1. Figure: A grid with horizontal (x) and vertical (y) dimensions
Activity 18.2.1.
11-9-1: Where is x = 0 y = 0 on an image?
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Middle of the image in width on the left side
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y is 0 at the top left corner
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Top right corner of the image
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x is 0 at the left corner
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Middle of the image in width and height
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y is 0 at the top left corner and x is 0 on the left
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Top left corner of the image
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Correct! x is 0 and y is 0 at the top left corner of the image
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Bottom left corner of the image
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y is 0 at the top and increases towards the bottom
Activity 18.2.2.
11-9-2: What color would red = 255, green = 0, blue = 0 be?
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black
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Black is an absence of light (all values are 0).
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white
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White is when all values are 255.
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red
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If the green and blue are 0 and the red is 255 this will be red.
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green
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This would be true if the green was 255 and the other values were 0.
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blue
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This would be true if the blue was 255 and the other values were 0.
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