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18.6. Changing Step 3: Changing which data we use

Below is a selection of images that you can use in the programs in this section.

We can also change which part of the picture we read and manipulate. When we are changing several colors at once we can create a new pixel with the desired color using Pixl(red,green,blue) as shown below on line 20.

# STEP 1: USE THE IMAGE LIBRARY from image import * # STEP 2: PICK THE IMAGE img = Image("vangogh.jpg") # STEP 3: SELECT THE DATA halfWidth = (int) (img.getWidth() / 2) halfHeight = (int) (img.getHeight() / 2) for x in range(halfWidth): for y in range(halfHeight): # STEP 4: GET THE DATA p = img.getPixel(x, y) r = p.getRed() g = p.getGreen() b = p.getBlue() # STEP 5: CREATE THE COLOR newPixel = Pixel(255-r, 255-g, 255-b) # STEP 6: CHANGE THE PIXEL img.setPixel(x, y, newPixel) # STEP 7: SHOW THE RESULT win = ImageWin(img.getWidth(),img.getHeight()) img.draw(win)

What happens if we skip every other x and y as we manipulate the colors? Maybe make the green 255 and the blue 0?

# STEP 1: USE THE IMAGE LIBRARY from image import * # STEP 2: PICK THE IMAGE img = Image("vangogh.jpg") # STEP 3: SELECT THE DATA for x in range(0,img.getWidth(),2): for y in range(0,img.getHeight(),2): # STEP 4: GET THE DATA p = img.getPixel(x, y) r = p.getRed() # STEP 5: CREATE THE COLOR newPixel = Pixel(r, 255, 0) # STEP 6: CHANGE THE PIXEL img.setPixel(x, y, newPixel) # STEP 7: SHOW THE RESULT win = ImageWin(img.getWidth(),img.getHeight()) img.draw(win)

Let’s try side-to-side copying.

# STEP 1: USE THE IMAGE LIBRARY from image import * # STEP 2: PICK THE IMAGE img = Image("vangogh.jpg") # STEP 3: SELECT THE DATA halfway = (int) (img.getWidth() / 2) for x in range(halfway): for y in range(img.getHeight()): # STEP 4: GET THE DATA p = img.getPixel(x, y) r = p.getRed() g = p.getGreen() b = p.getBlue() # STEP 5: CREATE THE COLOR newPixel = Pixel(r, g, b) # STEP 6: CHANGE THE PIXEL img.setPixel(halfway + x, y, newPixel) # STEP 7: SHOW THE RESULT win = ImageWin(img.getWidth(),img.getHeight()) img.draw(win)

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Q-4: Try it: How would you mirror the image from left-to-right around a vertical line in the middle of the picture? Try changing line 22 to these. If you get it right it will look like the women is nose to nose with herself.

• img.setPixel(halfway - x, y, newPixel)
• It does mirror, but only the left half
• img.setPixel(x - halfway, y, newPixel)
• This creates two copies of the left half
• img.setPixel(img.getWidth() - 1 - x, y, newPixel)
• Yes, it looks like the woman is kissing herself
• img.setPixel(x - img.getWidth(), y, newPixel)
• No, no effect.

Copy the pixels in the top left quadrant to the the bottom right quadrant. Look at the picture above for the expected result.

# USE THE IMAGE LIBRARY from image import * # PICK THE IMAGE img = Image("vangogh.jpg") # SELECT THE DATA halfwayWidth = (int) (img.getWidth() / 2) halfwayHeight = (int) (img.getHeight() / 2) for x in range(halfwayWidth): for y in range(halfwayHeight): # GET THE DATA p = img.getPixel(x, y) r = p.getRed() g = p.getGreen() b = p.getBlue() # CREATE THE COLOR newPixel = Pixel(r, g, b) # CHANGE THE PIXEL img.setPixel(halfwayWidth + x, halfwayHeight + y, newPixel) # SHOW THE RESULT win = ImageWin(img.getWidth(),img.getHeight()) img.draw(win)

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