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Lab 06: Graphics Part I: Making Photoshop Functions


  • Create functions to manipulate images

Image Transformations

You've probably used a variety of graphics editors such as Paint, Photoshop, GIMP, etc. to manipulate or enhance your pictures. In this lab session, you will be exploring and creating functions to transform your images in the same way these image editors are able to.

Image transformations are operations that change the appearance of an image or its spatial location. Common image transformations include resize (shrink or enlarge), rotate, crop, translate (i.e move), and flip. There are also functions to change the color or brightness of an image.

In this lab, we will explore four functions: resize, colorize, translate and paste. At the end of this session, you will be able to use this functions (and create your own) to transform your images into beautiful mosaics. Once again, you are only limited by your imagination and creativity.

Resizing an Image: Shrinking and Enlarging

Below is a program that takes an image and shrink it by a specified factor, F. For instance, if the original image is 1000x1000 pixels and you wanted to shrink it by a factor of 5, you would end up with an image of size 200x200.

from Myro import *

def main():
    # read an image and display it
    oldPic = makePicture("http://wiki.roboteducation.org/wiki/images/4/4d/Butterfly1.gif")
    show(oldPic, "Before")
    X = getWidth(oldPic)
    Y = getHeight(oldPic)
    # Input the shrink factor and computer size of new image
    F = int(ask("Enter the shrink factor."))
    newx = int(X/F)
    newy = int(Y/F)
    # create the new image
    newPic = makePicture(newx, newy)
    for x in range(newx):
        for y in range(newy):
            setPixel(newPic, x, y, getPixel(oldPic, x*F, y*F))
    show(newPic, "After")


The image below on the right is 425x400 pixels in dimension. After shrinking it by a factor of 2, the result is the image on the right with dimensions 212x200.

Original Image (425x400) After Shrinking (212x200, F=2)

Exercise 1: Write a function (resize) that gives the user the option to enlarge or shrink an image by some factor. The user should have the option to choose this factor as well. Your function should display the new image after it has been resized.

Changing Colors in your Image

In the previous labs, you've manipulated the pixels in the pictures your robot take to identify various objects such as the orange pyramid. In this section you will experiment with changing colors in other images (these do not have to be pictures your robots take). Recall that you can define your own colors using the makeColor function. For instance, to define a color called awesomeness with RGB values 156,120,47 you would use the following code:

awesomeness = makeColor(156,120,47)

Also, you can load pictures from your computer with the makePicture() function:

mySavedPicture = makePicture("robots.jpg")

To navigate and then select the image to load, use the following combination:

mySavedPicture = makePicture("http://wiki.roboteducation.org/wiki/images/4/4d/Butterfly1.gif")

You can also use makePicture(pickAFile()) to select and load a picture from your computer. When you call the pickAFile command, a navigational dialog box is displayed. You can use this to navigate to any folder and select a file to open most any image.

The red pixels in the first butterfly below have been changed to blue and its yellow pixels to red.

Butterfly1.gif<--- Butterfly1 Butterfly2.gif<--- Butterfly2

You can get the original butterfly (on the left) with this command:

>>> butterfly = makePicture("http://wiki.roboteducation.org/wiki/images/4/4d/Butterfly1.gif")

Exercise 2: Write a program that takes butterfly1 and changes two or more of the colors in the image to produce an output like butterfly2. To use image butterfly1, use the URL string "http://wiki.roboteducation.org/wiki/images/4/4d/Butterfly1.gif", or right-click on the image and select Save Image As and use the file name or pickAFile().

Copying and Pasting an Image

Copying an image can prove useful in image transformations and other applications. Below you will find functions for copying and pasting an image onto a canvas.

from Myro import *

def makeGray(pic):
    pic2 = copyPicture(pic)
    for pix in getPixels(pic2):
        r, g, b = getRGB(pix)
        gray = (r + g + b) / 3
        setRGB(pix, gray, gray, gray)
    return pic2

def paste(pic1, x, y, pic2):
    newpic = copyPicture(pic1)
    for col in range(getWidth(pic2)):
        for row in range(getHeight(pic2)):
            setPixel(newpic, col + x, row + y, 
                     getColor(getPixel(pic2, col, row)))
    return newpic

def main():
   butterfly = makePicture("http://wiki.roboteducation.org/wiki/images/4/4d/Butterfly1.gif")
   bigpic = makePicture(500, 500)
   bigpic = paste(bigpic, 10, 10, butterfly)
   bigpic = paste(bigpic, 200, 200, makeGray(butterfly))


Assignment 06: Adding More Functions to your Photoshop Library

Part I
Exercises 1 and 2 of Lab 8

Part II
1. Horizontal Flip: Write a function that will flip an image horizontally as displayed below:

2. Collage: Write a program to create a mosaic of images on your canvas. Your functions should utilize the translate, horizontal flip and the colorize function you create in class. Please Include your collage with your program (do not worry about printing it in color, greyscale is acceptable).

Links to Course-Related Pages