Picture Lab Activity 8

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Creating a collage

You can copy one picture to another by copying the color from the pixels in one picture to the pixels in the other picture. To do this you will need to keep track of the row and column information for both the picture you are copying from and the picture you are copying to, as shown in the following copy method. The easiest way to do this is to declare and initialize both a fromRow and toRow in the outer for loop and increment them both at the end of the loop. A for loop can have more than one variable declaration and initialization and/or modification. Just separate the items with commas. Note that the inner loop has both a fromCol and a toCol declared, initialized, and incremented.

public void copy(Picture fromPic,  int startRow, int startCol)
    Pixel fromPixel = null;
    Pixel toPixel = null;
    Pixel[][] toPixels = this.getPixels2D();
    Pixel[][] fromPixels = fromPic.getPixels2D();
    for (int fromRow = 0, toRow = startRow;
         fromRow < fromPixels.length && toRow < toPixels.length;
         fromRow++, toRow++)
      for (int fromCol = 0, toCol = startCol;
           fromCol < fromPixels[0].length && toCol < toPixels[0].length;
           fromCol++, toCol++)
        fromPixel = fromPixels[fromRow][fromCol];
        toPixel = toPixels[toRow][toCol];

You can create a collage by copying several small pictures onto a larger picture. You can do some picture manipulations like zero blue before you copy the picture as well. You can even mirror the result to get a nice artistic effect (Figure 11).

The following method shows how to create a simple collage using the copy method.

public void createCollage()
    Picture flower1 = new Picture("flower1.jpg");
    Picture flower2 = new Picture("flower2.jpg");
    Picture flowerNoBlue = new Picture(flower2);

Notice that the Picture method write can be used to save a copy of the final collage to your disk as a JPEG picture file. You can also specify the full path name of where to write the picture (“c:\temp\collage.jpg”). Be sure to include the extension (.jpg) as well so that your computer knows the file type.

You can test this with the testCollage method in PictureTester.


  1. Create a second copy method that adds parameters to allow you to copy just part of the fromPic. You will need to add parameters that specify the start row, end row, start column, and end column to copy from. Write a class (static) test method in PictureTester to test this new method and call it in the main method.
  2. Create a myCollage method that has at least three pictures (can be the same picture) copied three times with three different picture manipulations and at least one mirroring. Write a class (static) test method in PictureTester to test this new method and call it in the main method.