pictures looping through pixels.. lab review (1) objects instantiated from class turtle mytut =...
TRANSCRIPT
Pictures
Looping through pixels.
Lab Review (1)
Objects Instantiated from Class Turtle myTut = new Turtle(myWorld); new operator creates an instance of the
class Constructor
Constructs (initializes) object Has same name as class May need to supply arguments as
parameters
Lab Review (2)
Methods Send message to object by calling
method myTut.turnLeft();
Argument can be supplied as a parameter myTut.forward(45);
Lab Review (3)
/** * Draws a square with side width pixels at the current position * in the world. * * @param width length of the side */public void drawSquare(int width){ //draw side one this.forward(width); // turn 90 deg counterclockwise this.turnLeft(); // draw side two …}
For main program:
/** This program draws uses the Turtle to draw nested squares.
@author S. Sigman @version 2/4/2007 */
Lab Review (4)
Using the Java packages require that the class or classes be made available to the compiler.
import statement used to do this import java.awt.Color; Put at top of the file import java.awt.*; makes all classes in
java.awt available.
Problem
Manipulate a digital image make a picture brighter/darker alter the color in a picture
In computer science we must often start by learning about the domain in which we are writing programs. Often requires us to learn more about our
language
Digital Images
How are images encoded? Basic Idea: Represent image as a 2-
dimensional matrix of colored dots. Human Visual Perception
Humans have low visual acuity We see color and luminance (black and white)
using different neural pathways in our brain Luminance is perceived with our peripheral
vision
Digital Images - Arrays
Arrays are a contiguous collections of cells homogeneous data where each cell is identified by an index.
int [] score = {23, 25, 22, 25}; score[0] is 23; score[1] is 25; score[3] is ? Arrays are objects. The assignment above is a
shorthand that hides the new operator. int [] grades = new int [10]; // declares and
// allocates grades[0] = 35;
Digital Images – Matrices
Matrices are 2-dimensional arrays In Java a matrix is an array of arrays An image has type: Pixel [][] pictData;
0
1
0 1 2 3
Row Major Order
pictData [r] [c]
0 1 2 3
0
1
Column Major Order
pictData [c] [r]
Digital Images - Color
Visible light is continuous Wavelength: 370 nm – 730 nm
We have red, green, blue receptors red peak: 560 nm green peak: 550 nm blue peak: 425 nm
Color we see is based upon signals from recptors
Digital Images – Color Models
RGB – Red Green Blue HSV – Hue Saturation and Value CMYK – Cyan, Magenta, Yellow, Black
Used by printers
Digital Image - RGP
Three Channels Red, Green, Blue Value Range: 0 – 255 24 bit color
16 million colors Does not cover range of colors we perceive
32 bit color 16 million colors alpha channel – transparency
Creating an Image
String fileName = FileChooser.pickAFile();
Picture pict = new Picture(fileName);
// show the image
pict.show();
// explore the image
pict.expore();
Looking at Pixels
Pixel pix = pict.getPixel(0,0); int xCord = pix.getX(); int yCord =
pix.getY(); int redVal = pix.getRed(); pix.setRed(255); pix.setGreen(0);
pix.setBlue(0); pict.repaint(); // must repaint to show
// change
Looking at Pixels (2)
Pixel [] imgData = pict.getPixels();pict.getPixel(10,100).setColor(Color.black);
pict.getPixel(11,100).setColor(Color.black);
pict.getPixel(12,100).setColor(Color.black);
pict.getPixel(13,100).setColor(Color.black);
pict.repaint(); This process is a little laborious!!
Changing The Green Component For All Pixels
Push the green component to 255 for all pixels.
Algorithm Get an array of pixels in image For each pixel in the image
set the green component to 255
How do we do the for each?
The For Each Loop
Allows us to repeat a set of Java commands for each element in an array.
Syntax for (type variableName: array)
statement; for multiple statements enclose in { }
Method to Maximize Green
public void maxGreen() { // get the pixels Pixel [] pixels = this.getPixels(); // set the pixels to max green for(Pixel curPix : pixels) {
curPix.setGreen(255); }}
While Loops
Java provides other ways to construct loops
While loop loop while some condition is true syntax
while (test)
statement; Advice: always use braces
Maximize Green With a While Loop
public void maxGreen() { // get the pixels Pixel [] pixels = this.getPixels(); // set the pixels to max green int curPos = 0; while (curPos < pixels.length) {
pixels[curPos].setGreen(255); curPos++; // same as curPos = curPos + 1; }}
For Loop
Loop with a built-in counter – also called a counting loop
Syntax for (init; limit test; change)
statement; Advice: always use braces
Maximize Green With a For Loop
public void maxGreen() {
// get the pixels
Pixel [] pixels = this.getPixels();
// set the pixels to max green
for (int i=0;i < pixels.length; i++) {
pixels[i].setGreen(255);
}
}
Scope
For loop from previous slidefor (int i=0;i < pixels.length; i++) {
pixels[i].setGreen(255); }
Where is i’s value know? Just inside the block the defines the body of
the loop. This is i’s scope. Look at scope in Picture. Principle: Variables scope should be as
small as possible. Called localization.