Multiple If’s with Images

We can use multiple if’s to reduce the number of colors in an image. Let’s say that if we have a little bit of each of red, green, and blue, we want to make each of them zero. If we have more, we set them to a mid-range value like 120. This is called posterizing because it reduces all the colors in a picture to a small number of colors – like the ones you might use if you were making a poster.

from image import * # CREATE AN IMAGE FROM A FILE img = Image("arch.jpg") # LOOP THROUGH ALL PIXELS for x in range(img.getWidth()): for y in range(img.getHeight()): p = img.getPixel(x, y) r = p.getRed() g = p.getGreen() b = p.getBlue() # VALUES FOR THE NEW COLOR if r < 120: r = 0 if r >= 120: r = 120 if g < 120: g = 0 if g >= 120: g = 120 if b < 120: b = 0 if b >= 120: b = 120 # CREATE THE COLOR newPixel = Pixel(r,g,b) # CHANGE THE IMAGE img.setPixel(x, y, newPixel) # SHOW THE CHANGED IMAGE win = ImageWin(img.getWidth(),img.getHeight()) img.draw(win)

Rewrite the code for posterizing an image using if and else rather than multiple if’s. Test that it still works correctly.

csp-15-4-2: How many different colors will be in our image when we are done?

• 8
• Two possible values of each of red, green, and blue (3 colors) is 2 raised to 3rd power combinations which is 8.
• 3
• Two values of each of red, green, and blue is more than 3.
• 120
• Far fewer
• 16,777,216 (= 256 * 256 * 256)
• That's the total number of colors possible. But this code reduces that.

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