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| Figure 3 . Output text on the command line screen. |
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java version "1.6.0_14"
Java(TM) SE Runtime Environment (build 1.6.0_14-b08)Java HotSpot(TM) Client VM (build 14.0-b16, mixed mode,
sharing)javac 1.6.0_14
Dick BaldwinPicture, filename Prob02.jpg height 274 width 365 |
The algorithm
The algorithm required to transform the image from Figure 1 to Figure 2 is:
A color value is inverted by subtracting the value from 255 and using the difference as the new color value.
Obvious that the blue color value is reduced to zero
It should be obvious to the student when comparing the two images in the PictureExplorer objects that the blue pixel value has been set to zero for every pixel in the modified image.
Color inversion is not quite so obvious
Deducing that the red and green colors in the output pixels are the inverse of the red and green colors in the input image isn't quite as straightforward.However, using algebra to compare several corresponding pixels in the two images should make it obvious fairly quickly to the curious student.
The implementation of the algorithm will be explained below.
Will explain in fragments
I will explain this program in fragments. A complete listing is provided in Listing 6 near the end of the module.
I will begin with the driver class named Prob02 , which is shown in its entirety in Listing 1 .
| Listing 1 . The driver class. |
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public class Prob02{//the driver class
public static void main(String[]args){
Prob02Runner obj = new Prob02Runner();obj.run();System.out.println(obj.getPicture());}//end main
}//end class Prob02 |
You should already be familiar with everything in Listing 1 . The most important aspect of Listing 1 for purposes of this discussion is the call to the run method belonging to the object instantiated from the Prob02Runner class. I will explain the run method shortly.
Beginning of the class named Prob02Runner
The class definition for the class named Prob02Runner begins in Listing 2 .
| Listing 2 . Beginning of the class named Prob02Runner. |
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class Prob02Runner{
private Picture pic = new Picture("Prob02.jpg");public Prob02Runner(){//constructor
System.out.println("Dick Baldwin");}//end constructor
//----------------------------------------------------////Accessor method
public Picture getPicture(){return pic;} |
Again, you should be familiar with everything in Listing 2 . I will simply highlight the instantiation of a new Picture object using an image file as input and the saving of a reference to that object in the private instancevariable named pic .
The beginning of the run method
The run method begins in Listing 3 . This is where the action is, so to speak.
| Listing 3 . The beginning of the run method. |
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public void run(){
pic.addMessage("Dick Baldwin",10,20);pic.explore(); |
You are already familiar with the call to the addMessage method to add my name as text to the image encapsulated in the Picture object. ( See Figure 1 .)
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