CS 151: Project #4

Project 4: The Warhol Project

Main course page

The purpose of this project is to make a collection of images in the style of Andy Warhol. You'll do this by manipulating the pixel colors of an image.


Make sure you have copies of the graphics.py and display.py files.

You can grab your picture from the photo directory.

For this assignment you're going to create two python programs. One will generate a Warhol style collage. The other will change the blue screen to a different color. Both will write their results to an image file, which you can then view with your show program.

  1. In your filter.py file, create a function putPixmap which takes four arguments. The first argument will be a destination Pixmap, the second argument will be a source Pixmap, and the last two arguments will be an x, y location to place the second Pixmap into the first. The function outline in comments is given below.

    For each comment inside the function below, you need to write one line of python code.

    # place src into dst with upper left at x, y in dst
    def putPixmap( dst, src, x, y ):
        # loop over each row i in src
            # loop over each column j in src
                # from src, get the (r, g, b) value at pixel (j, i)
                # in dst, set location (x + j, y + i) to (r, g, b)
        # return

    Once you have written your function, you can use this file to test it. Run the test program on the command line and give it an image filename as its argument. For example:

    python testPutPixmap.py miller.ppm

    Remember that the Zelle graphics package can read only PPM type images.

  2. Create three more functions like swapRedBlue that edit the colors in a Pixmap to achieve some effect. See if you can emulate some of the Instagram effects.
  3. Your main warhol program should read in one image, create four copies of it, use your manipulation functions to change their colors, create a new blank image that is width*2 by height*2 and then use the putPixmap function to insert the four edited images. Finally, it should write out the collage image.
    def main(argv):
        # if the length of argv is less than 2
            # print a usage statement
            # exit
        # read in the Pixmap from argv[1], put the result into a variable (e.g. pmap)
        # clone pmap and assign it to a new variable (e.g. map1)
        # call your first manipulator function on the clone
        # clone pmap and assign it to a new variable (e.g. map2)
        # call your second manipulator function on the clone
        # clone pmap and assign it to a new variable (e.g. map3)
        # call your third manipulator function on the clone
        # clone pmap and assign it to a new variable (e.g. map4)
        # call your fourth manipulator function on the clone
        # create a new Pixmap that is 2*width x 2*height and store it in a new variable
        # put map1 into the collage at (x, y) = (0, 0)
        # put map2 into the collage at (0, height)
        # put map3 into the collage at (width, 0)
        # put map4 into the collage at (width, height)
        # save the map to a file
        # return

    Finish up this task by putting a call to main inside the conditional statement we've used before. Then call your python program and view the collage.

  4. Your last task is to create a python program that reads in your blue-screen image and turns the blue-screen pixels to a different color. The rest of the pixels should remain untouched. You will need to loop over each pixel in the image and test if it is very blue. If it is very blue, change its color. Otherwise, leave it alone.

    A reasonable test for 'very blue' is if the blue channel is at least twice the red channel and also bigger than the green channel.



Make a new wiki page for your assignment. Put the label cs151f12project4 on the page. Each of you needs to make your own writeup.

In addition to making the wiki page writeup, put the python files you wrote on the Academics server in your handin directory.

Colby Wiki

In general, your writeup should follow the outline below.