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15.1. Using Decisions with Images

Learning Objectives:

• Show examples of using conditionals to modify images.

• Use conditionals to combine two pictures.

• Use if and else with images.

• Use multiple if statements with images.

We can create image effects by conditionally executing code. In the code below we will try to change the color of the women’s shirt. We will clear the red value (set it to 0) for any pixel that has a red value greater than 200 and a green value of less than 100 and a blue value of less than 100.

from image import * # CREATE AN IMAGE FROM A FILE img = Image("gal2.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 > 200 and g < 100 and b < 100: # CREATE THE COLOR newPixel = Pixel(0, g, b) # CHANGE THE IMAGE img.setPixel(x, y, newPixel) # SHOW THE CHANGED IMAGE win = ImageWin(img.getWidth(),img.getHeight()) img.draw(win)

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What happens if we only test if red is greater than 200? Change the code above to try it.

Can you find values that work well to only change the shirt color and not anything else?

Remember that white light is a combination of red, green, and blue light with each value at 255 for totally white light. Try to change just the white background to green.

Note

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