1. Getting and displaying
The Picture Object
Getting and displaying
Copyright © 2009 Curt Hill

2. How are pictures shown?
Any image displayed on a computer is a series of pixels
Pixel is an abbreviation of picture elements
It is a dot of a particular color and intensity
Each pixel has at least three components:
Red, Green, Blue
All of which are in the range 0-255
Copyright © 2009 Curt Hill

3. How are pictures organized?
Pictures are always lines of pixels
The lines are horizontal
The pictures are always rectangular
Each line is same length
Monitors are generally in the 1024 by 760 size
May be higher or lower depending on age and expense
Digital cameras usually make much larger images
Copyright © 2009 Curt Hill

4. How are pictures stored?
There are many formats
JPEG – Joint Photograph Expert Group
Usually have a .JPG extension on the file
GIF – Graphic Interchange Format
Owned by CompuServe
PNG is the public domain alternative
Bitmap – Native format for most PCs
Copyright © 2009 Curt Hill

5. Storage Most file formats compress the image in some way
Bitmaps generally the least
JPGs generally the best
GIFs are best for line drawings
Compression may be lossless or lossy
JPG is lossy but the amount of loss is a parameter to the compression process
Copyright © 2009 Curt Hill

6. Objects We will use the Java object named Picture and a few others
It will allows us to read from disk and write to disk JPGs
We will not have to worry about compression and other details
We will be able to access individual pixels as well as display the picture easily
Copyright © 2009 Curt Hill

7. Constructors Pictures like all other objects need a constructor
Recall there were two Turtle constructors with different parameters
One took just the World object
The other took an initial location and the World object
We will have multiple constructors with Picture as well
Copyright © 2009 Curt Hill

8. Picture Constructors
There is a default constructor: Picture pix = new Picture();
This creates a picture object but does not initialize it
The more helpful is the String constructor: Picture(String fileName);
The string is the file name of the picture
This could be a constant string or we could find it
Copyright © 2009 Curt Hill

9. View The string constructor makes the object
It then loads the actual picture into memory
It does not display it
This is done with the show method: p.show();
It creates a new window to display the picture
See the example program
Copyright © 2009 Curt Hill

10. Example public class PictureDemo1{
public static void main(String [] a){
Picture p = new Picture(
“C:/intro-prog-java/mediasources/barbara.jpg");
p.show(); }
Copyright © 2009 Curt Hill

11. What’s wrong with this picture?
The problem is the constant file name
Every time we run the program we get the same file
What we would really like is the ability to choose any picture file on the disk
We do this with FileChooser object
Copyright © 2009 Curt Hill

12. FileChooser FileChooser is an existing object
Produces a common dialog box screen that makes it easy to choose a file
The static method of the object that you want is called pickAFile
This returns a string
This can then be given to the Picture constructor
Copyright © 2009 Curt Hill

13. The Program
Copyright © 2009 Curt Hill

14. Started
Copyright © 2009 Curt Hill

15. Display
Copyright © 2009 Curt Hill

16. Commentary
The String declaration and call to FileChooser was made two lines so PowerPoint would not wrap
It could be: String fileName = FileChooser.pickAFile();
Displaying pictures is that easy
Copyright © 2009 Curt Hill

17. Now What? In order to do picture manipulation we need flow of control
This includes loops and conditionals
This is our next major topic (chapter 4)
However, a turtle can drop a picture onto its world
Copyright © 2009 Curt Hill

18. Turtles and Pictures
A turtle can place a picture on a world with the drop method
This method takes a Picture as a parameter
Something like this: Turtle t = new Turtle … Picture p = new Picture … … t.drop(p);
Copyright © 2009 Curt Hill

19. Commentary The picture is not resized
If the picture is too large it will be clipped by the world
The orientation of the picture matches the turtle
It will be shown tilted at the same angle as the turtle
Consider the following program
Copyright © 2009 Curt Hill

20. Example program public class PictureDemo1{
public static void main(String [] a){
String fileName;
fileName = FileChooser.pickAFile();
Picture p = new Picture(fileName);
World w = new World();
Turtle yertle = new Turtle(w);
yertle.forward(50);
yertle.drop(p);
yertle.turn(-50); }
Copyright © 2009 Curt Hill

21. Display
Copyright © 2009 Curt Hill

22. FileChooser Again FileChooser is a wrapper for the JFileChooser object
Part of the standard Java package
FileChooser is made to be easier to use
One problem with FileChooser is that it starts at the same directory
Depends on the system
In Windows usually MyDocuments
The directory to start in can be changed
Copyright © 2009 Curt Hill

23. setMediaPath A method that tells FileChooser where to start
Example: FileChooser.setMediaPath(“D:/intro-prog-java”);
Always use forward slashes rather than backslashes
Copyright © 2009 Curt Hill

24. Finally Next we must do a demo using Turtles
After that we figure out how to access and modify pixels
This is the next presentation
Copyright © 2009 Curt Hill