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.

Here is the reference guide to the graphics package.


Tasks

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

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 placePixmap 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 placePixmap( 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)
    

    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 testPlacePixmap.py miller.ppm

    If you look at the end of test program, you will see that it writes the output to a file called duplicate.ppm. You can use your show.py program to view the duplicate.ppm image. It should show two copies of the original image, side-by-side.

    As you are working with your code, remember that the Zelle graphics package can read only PPM type images.

    Once you are confident that your placePixemap function works, please remove the comments that we supplied. They don't help the reader understand the overall purpose of the code because they are a line-by-line annotation of what each line does. In most cases, that is obvious from the code itself. Helpful comments include the docstring (which you need to write), which explains the meaning of each parameter.

  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. Note: when we say "like swapRedBlue", we do not mean "variants of swapRedBlue". A filter that simply reorders the color channels will not count towards your three (though you are welcome to write them in addition to your three, if you like the effect).
  3. Your main warhol program (which you should put in a file named warhol.py) should read in one image, create four copies of it, use your filter functions to alter tham, create a new blank image that is width*2 by height*2 and then use the placePixmap function to insert the four edited images. Finally, it should write out the collage image. The code below is a skeleton of the algorithm.
    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)
        # clone pmap and assign it to a new variable (e.g. map2)
        # clone pmap and assign it to a new variable (e.g. map3)
        # clone pmap and assign it to a new variable (e.g. map4)
    
        # call your first manipulator function on map1
        # call your second manipulator function on map2
        # call your third manipulator function on map3
        # call your fourth manipulator function on map4
    
        # 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 big map to a file
    
    

    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.

    Tip: For this function, helpful comments would indicate the different sections of code (e.g. "read in one pixmap", "make 4 copies of it", "make an empty pixmap big enough to hold 4 copies of this one", and "put the 4 filtered images into the big one"). And, of course, a docstring is a must.

  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.


Extensions


Writeup

Make a new wiki page for your assignment. Put the label cs151s15project4 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 Courses server in your private directory in a folder named Project4.

Colby Wiki

In general, your writeup should follow the outline below.