1. CSC1401 Viewing a picture as a 2D image - 2

2. Review from the last week
We treated a picture as a 2 dimensional array, and used the getPixel(x,y) method to access each of the pixels
Since there were 2 dimensions (x and y), we needed a nested loop to access all of the pixels

3. Review A two-dimensional array has columns and rows
Use nested loops to work with 2-d arrays
One loop for the x direction and one for the y
for (int x = 0; x < this.getWidth(); x++) {
// loop through the rows (y direction)
for (int y = 0; y < this.getHeight(); y++)

4. Learning Goals Understand at a conceptual and practical level
How to copy pixels from one picture to another
How to copy pixels from one picture to a specified location in another picture
How to create larger or smaller pictures

5. Copying Pixels to a New Picture
Need to track the source picture x and y
And the target picture x and y 1 2 3 4 1 2 3 4

6. Copying Pixels to a New Picture1
What if we want to copy the target to a different location in the source
Than 0,0
Say startX and startY
What is an algorithm that will do this? 1 2 3 4 1 1 2 3 1 2 3 4 1 2 3

7. Copy Picture Algorithm
Copy a picture into another picture
Create the picture objects
Invoke the method on the target picture
Loop through the source picture pixels
Get the source and target pixels
Set the color of the target pixel to the color of the source pixel

8. Copy Algorithm to Code Loop through the source pixels
// loop through the columns
for (x = 0;
x < insertedPicture.getWidth();
x++) {
// loop through the rows
for (y = 0;
y < insertedPicture.getHeight();
y++)

9. Copy Algorithm to Code – Cont
Get the source and target pixels
copyPixel = insertPicture.getPixel(x,y);
targetX = ???;
targetY = ???;
targetPixel = this.getPixel(targetX,targetY);
Set the color of the target pixel to the color of the source pixel
targetPixel.setColor(copyPixel.getColor());

10. Creating a method
What parameters are needed?

11. Copy Method

12. Trying out our method Copying Katie onto the beach
I found an x value of 247 and a y value of 125 was a good location to copy her onto the beach (using the explore)

13. Scaling You can make a picture smaller You can make a picture larger
Faster to download on the web
Increment the source x and y by a number larger than 1
Don’t use all the source pixels in target
You can make a picture larger
Show more detail
Copy the same source x and y to more than one target x and y
Use source pixels more than once in target

14. Scaling Down a Picture
passionFlower.jpg is 640pixels wide and 480 pixels high
If we copy every other pixel we will have a new picture with width (640 / 2 = 320) and height (480 / 2 = 240) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 2 8 10

15. Scaling Down Algorithm
Create the target picture
Invoke the method on the target picture
Create the source picture
Loop with source x starting at 0 and target x starting at 0 as long as < source width
Increment the source x by 2 each time through the loop, increment the target x by 1
Loop with source y starting at 0 and target y starting at 0 as long as < source height
Increment the source y by 2 each time through the loop, increment the target y by 1
Copy the color from the source to target pixel

16. Scaling Down Method

17. Invoking the method
Picture smaller = stevepicture.decreasePicture (2);

18. Thinking Through Scaling Up1 2
Copy each pixel in the source multiple times to the target
Source (0,0) Target (0,0)
Source (0,0) Target(1,0)
Source (1,0) Target(2,0)
Source (1,0) Target(3,0)
Source (2,0) Target(4,0)
Source (2,0) Target(5,0)
Source (0,0) Target(0,1)
Source (0,0) Target(1,1) 1 2 3 4 5 6 1 1 2 3 4 5 1 2 3 4 5 6 1
What could we add to source x and source y so that it is 0 twice, then 1 twice, then 2 twice, etc.
Remember that 0.5 is 0 when you cast to integer. 2 3

19. Scaling Up Algorithm Create the target picture
Invoke the method on the target picture
Loop with source x starting at 0 as long as < source width
Loop with source y starting at 0 as long as < source height
Loop another x from 0 up to the factor of multiplication
Loop another y from 0 up to the factor of multiplication
Copy the color from the source to target pixel
The source x and y will need to be double variables. Cast them to int to lose the fractional part to get the pixel x and y.

21. Scaling Up Exercise
Write a method copyFlowerBigger to scale up the picture flower1.jpg when you copy it to 640x480.jpg
Save the result to a file using
pictureObj.write(“file”);

22. Summary To copy pixels from one picture to another
Keep track of the sourceX, sourceY and targetX and targetY
To copy one picture to a location in another
Just keep track of the values for targetX and targetY

23. Assignment
Review Media Computation Chapter 5, Section 2