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