CSC111 Lab 7 2014

--D. Thiebaut (talk) 12:45, 10 March 2014 (EDT)

---

Page under construction!

This lab presents image-processing operations in Python using JES. You will need to submit the last working version of your program by the end of the lab.

References

• A very good reference can be found here.
• A list of all the JES functions that apply to image processing can be found here.

Images

• It turns out that the new version of JES also works on JPG images as well at BMP images, so for this lab you can use the cat and baby with red eyes we saw in class, or pictures of your own choosing. One recommendation, though: the larger the image you pick, the more time you'll have to wait for your programs to process your image.

• redEyes.bmp
• catHat.bmp

JES and Image Processing

Skeleton Program

Below is a program you should copy/paste to your JES window.

# JES Picture processing
# D. Thiebaut
# A demo of some of the functions available in JES for manipulating 
# the pixels of an image.


# the image we are playing with
image = None

# changeColor( image ).
# Changes the amount of red, green and blue that is in an image
def changeColor( image ):
  for x in range(0,getWidth(image)):
    for y in range(0,getHeight(image)):
        pixel = getPixel (image, x, y)
        red   = getRed(pixel)
        green = getGreen(pixel)
        blue  = getBlue(pixel)
  
        # the line below replaces the pixel with its original color.  Change
        # the amount of red, green and blue to see some change in the colors
        newColor = makeColor( red, green, blue )
        setColor( pixel, newColor )
  return image

# ==================================================================  
#                             MAIN PROGRAM
# ==================================================================  
file = pickAFile()
image = makePicture( file ) 
show( image )
  
image = changeColor( image )
repaint( image )

• Run it to verify that it displays your image. Right now the program doesn't modify any pixel, so do not expect anything different from the original.

Problem 1: random processing

Add a new function to your JES program that modifies the red, green and blue components of each pixel. Here are different modifications you can try (be imaginative and try others too). Don't limit to just one component: apply the modification to all 3!

if blue <125  :
    blue = 0
else:
    blue = 255

blue = ( blue + red ) // 2
red = ( red + green ) // 2
green = ( green + blue ) // 2

blue = blue // 2	make blue component darker
blue = blue + (255-blue)//2	make blue component lighter
applies a threshold and create "patches" of colors
not sure how to call this one!

• 
  what transformation produced the image on the right?

Problem 2: black and white

• Make your image black and white by storing the same value in the green, red, and blue component of a pixel. In a first step, pick the amount of red of the pixel and store that number in the 3 components.

• Next take the average amount of red, green and blue and store that value (store it in a variable called grey for example), in all three components.

• Better: initial the grey variable as follows:

  grey  = int( 0.3 * red +0.6 * green +0.11 * blue )

Problem 3

Copy paste this function that contains a call to repaint( image ) inside the for x in range(...) loop. See how the program "sweeps" through the image.

• Modify the function so that the sweep goes from left to right.

• Modify the function so that the sweep goes from top to bottom

• Modify the function so that the sweep goes from bottom to top

Problem 4

Pick one of the functions you have written for the problems above and make a new copy of it under a different name.

Replace the nested for-loop with this loop:

    for x in range( getWidth( image ) ):
        for y in range( min( x, getHeight( image ) ):

Predict the way the image is going to be transformed by these nested for-loops. Then run it!

Problem 5: Border

Write a new function called addBorder( image, borderWidth ) that will put a red border around the image.

Modify the program and ask the user to pick a color first, then pass this color to the function addBorder( image, borderWidth, color ) which will put a border all around the image.

Problem 6: B&W image with Colored Border

Make your program output a version of your colored image that will be black and white with a colored border around it.

Problem 7: Diagonal

• Replace the nested for-loops by this single loop like this:

     for x in range(0,getWidth(image)): 
         y = min( x, getHeight( image )-1 )
         pixel = getPixel (image, x, y)
         ...

and set the color of that pixel to red. What do you get?

• Modify your function so that it puts a red diagonal cross over the image.