Lab 3: Fun with Images --- or Photoshop is not Magic!

In this lab you will incorporate image processing into Python programming

1. Cut and paste the files image.py and imtest.py into your directory. Make sure to save the first file using the same file name. Don't worry about the code in image.py, it will only imported into your code and not modified. If you are working from a non-lab computer you may also need to download and install Python Imaging Library
2. The image.py library contains the following functions with indicated uses:

             Function                 Usage
   
           FileImage           myImage = FileImage("pic.jpg")  Reads in an image
   	show                myImage.show("title")  Displays the image in a window with given title
           copy                newImage = myImage.copy()   Creates a copy     
           redraw              myImage.redraw()   Redraws image after changes have been made
           EmptyImage          eImage = EmptyImage(width,height)  Creates a color image of indicated size
                                                                  and initializes color to (0,0,0)
           copyGray            grayImage = myImage.copyGray()  Creates a grayscale image from a color image
           save                newImage.save("newimage.jpg")  Saves image in the indicated format
       
           getPixel2D          (r,g,b) = myImage.getPixel(x,y)  Returns (r,g,b) for color image
                               intensity = grayImage.getPixel2D(x,y)  Returns integer grayscale between 0 and 255 
           setPixel2D          myImage.setPixel2D(x,y,(r,g,b))  Sets color at (x,y) to (r,g,b)
                               grayImage.setPixel2D(x,y,intensity)  Sets gray level at (x,y) to integer intensity
           getHeight           height = myImage.getHeight()
           getWidth            width = myImage.getWidth()
   

3. Cut and paste the image jack.jpg into your directory. Read through the file imtest.py and try to understand what it will do, then run it entering jack.jpg when prompted for an image name and see the result.
4. Rewrite the program so that the green component is removed and the red and blue components are retained.
5. Write a program that reads in an image and creates a new image that has flipped the original horizontally (i.e. y coordinates remain the same and x coordinates are flipped).
6. Repeat, but now flip the image vertically.
7. Cut and paste the images jackdark.jpg, jackfade.jpg, jackbright.jpg into your directory. These are grayscale images that have "bad contrast". The problem is that in each case, the range of grayscale values is compressed into an interval much smaller than the full range [0,255]. The contrast can be improved by doing the following:
   • Reading through all of the pixels and finding both the smallest and largest grayscale value in the image, say minGray and maxGray.
   • Rescaling the image as follows:

              newGray =int((255.0*(oldGray-minGray))/(maxGray-minGray))
      
            Note that if oldGray=minGray then newGray = 0 and if oldGray = maxGray then newGray = 255.
            That is, the interval [minGray,maxGray] is scaled to [0,255]
     

8. Write a Python program that reads in a grayscale image and performs the above steps to enhance the contrast. Try it on the three given "bad images".