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Lab 08: Graphics Part II: Making Photoshop Functions


  • Create functions to manipulate images

Image Transformations

You've probably used a variety of graphics editors such as Paint, Adobe 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 three functions: resize, colorize and paste. At the end of this session, you will be able to use this functions 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.

def main():
    # read an image and display it
    oldPic = makePicture(pickAFile())
    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 = X/F
    newy = 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:

myRed = makeColor(254, 0, 0)

Also, you can load the 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(pickAFile())

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 as any JPEG image. I

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

Butterfly1.JPG<--- Butterfly1 Butterfly2.JPG<--- Butterfly2

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, right click on the image and select Save Image As.

Translating an Image

In this section you will apply what you already know about Graphics to another type of image transformation, translation. A translation is simply a movement in the x,y plane of your window. When you were introduced to graphics, you created a variety of polygons as well as points and lines, drew these objects in a graphics window and then manipulated them in various ways. You can also treat an image like an object and move it around in your canvas in the same way you did with rectangles, circles etc. To convert a picture your robot takes into an image, use the following:

picture = takePicture()
pixmap  = makePixmap(picture)
image = Image(Point(x, y), pixmap)

If the picture was taken by your camera or downloaded from the web, you will need to use the makePicture command first so that the Myro commands will work on it. The code below creates two pixmap images, draws these images on a canvas and then translates them within the canvas using the move command.

def translate():
    myCanvas = GraphWin("My BigCanvas", 400, 400)
    oldPic = makePicture(pickAFile())
    pixmap  = makePixmap(oldPic)
    butterfly1 = Image(Point(50, 50), pixmap)
    butterfly2 = Image(Point(300, 300), pixmap)

The picture you choose must be smaller than your canvas. An ideal size is 100x100. The images below show the translation of two butterflies. As specified by the code above, butterfly1 starts out in the upper left corner and is translated 50 pixels along the x axis and the y axis. Butterfly2 starts out near the lower right corner and is translated -50 pixels along the x axis and the y axis.

Translate1.JPG <--- Before Translation Translate2.JPG <--- After Translation

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 createCanvas():
    canvas = GraphWin("My BigCanvas", 200, 200)
    pic = makePicture(pickAFile())
    return [pic, canvas]

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():
    [pic1, myCanvas] = createCanvas()
    pic2 = makeGray(pic1)
    newpic = paste(pic1, 0, 0, pic2)
    newpic = colorize(newpic, 0, 0, yellow)
    #drawing original pic
    pixmap  = makePixmap(pic1)
    image1 = Image(Point(50,50), pixmap)
    #drawing copied pic
    pixmap  = makePixmap(newpic)
    image1 = Image(Point(150,150), pixmap)


To the right is the product of copying and pasting a butterfly image. The result is a gray-scaled image of the original butterfly. CopyPaste.JPG

Assignment 08: Adding More Functions to your Photoshop Library

Part I : Exercises 1 and 2 of Lab 8

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

Links to Course-Related Pages