CS 100 - Computer Literacy, Spring 2005

Lab 7

This assignment will have you take an image and create a new image that will display the original picture multiple times. For example, take the following image of George Washington.

This image shown in twice side-by-side/horizontally would be:

Duplicating an Image Side-by-Side

Next we need a loop to access each pixel from the original image. Each pixel must be put into the duplicated image twice, once on the left side and once on the right side. We can use getColor() to get the pixel's color information from the original image and use setColor() twice to put that color information into the duplicated image. The only remaining question is:

"Where does the color information get put in the duplicated image?"

To answer this question let us assume we are dealing with an original image of 100x150 pixels. Hopefully by understanding what is done with this example, we can determine how to deal with this for any image.

• The original image will have
  • its upper left corner at pixel 1,1
  • its upper right corner at pixel 100,1
  • its lower left corner at pixel 1,150
  • its lower right corner at pixel 100,150
• The duplicated image image needs to have the same height with twice the width of the original picture. So its size would be 200x150 pixels.
• The duplicated image can be thought of as having two different sections. One section will hold the left side image. The other section will hold the right side image.
• The left side image will have
  • its upper left corner at pixel 1,1
  • its upper right corner at pixel 100,1
  • its lower left corner at pixel 1,150
  • its lower right corner at pixel 100,150
• The right side image will have
  • its upper left corner at pixel 101,1
  • its upper right corner at pixel 200,1
  • its lower left corner at pixel 101,150
  • its lower right corner at pixel 200,150
• The color information from the pixel at position 1,1 (the upper left corner) in the original image would need to be placed in both the left side image and the right side image of the duplicated image. This would be at the pixels with position of 1,1 and 101,1.
• The color information from the pixel at position 5,2 (close to the upper left corner) in the original image would need to be placed in both the left side image and the right side image of the duplicated image. This would be at the pixels with position of 5,2 and 105,2.
• The color information from the pixel at position 98,142 (close to the lower right corner) in the original image would need to be placed in both the left side image and the right side image of the duplicated image. This would be at the pixels with position of 98,142 and 198,142.
• We have a pattern here! The color information from the pixel at position X,Y in the original image would need to be placed in both the left side image and the right side image of the duplicated image. This would be at the pixels with position of X,Y and 100+X,Y.
• Also note that the value of 100 is the width of the original picture! Thus for any picture, the color information from the pixel at position X,Y in the original image would need to be placed in both the left side image and the right side image of the duplicated image. This would be at the pixels with position of X,Y and (width_of_the_original_image)+X,Y.

The following JES code shows how this is done:

Program to duplicate an image within another image

def duplicateHorz(): #Allow the user to pick up an image file file = pickAFile() #now convert the image in JES format pic = makePicture(file) # get the size of the originalimage origWidth = getWidth(pic) origHeight = getHeight(pic) # determine the size of new image newWidth = origWidth * 2 newHeight = origHeight #now creat a new image in JES format new_pic = makeEmptyPicture(newWidth, newHeight) # Loop for each pixel in the original image. # Put that pixels color information in two positions # in the new duplicated image. for orig_pixel in getPixels(pic): # get X and Y positions of pixel from new image x = getX(orig_pixel) y = getY(orig_pixel) # get the color from original pixel c = getColor(orig_pixel) # set the color to the pixel in the left side to c left_pixel = getPixel(new_pic, x, y) setColor(left_pixel, c) # set the color to the pixel in the right side to c right_pixel = getPixel(new_pic, x+origWidth, y) setColor(right_pixel, c) #Now display the new image show(new_pic) # save the new image writePictureTo(new_pic, pickAFile())

Lab Assignment 7

Modify the above code in two different ways.

1. Write a function triplicateHorz() that will produce three images side-by-side/horizontally. Doing this to the George Washington image we would get:
   
2. Write a function duplicateVert() that will produce two images one on top of the other (i.e. vertically). Doing this to the George Washington image we would get:
   

We would like to see any resulting images posted on the lab 7 page on CS 100 Swiki.

Try to use a small image when running your program. Some images from our textbook can be found at http://www.cs.uic.edu/~i100/images/other/index.html.