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Manipulating Pictures, Arrays, and Loops part 1

Manipulating Pictures, Arrays, and Loops part 1. Digital Pictures. Represented by pixels With a red, green, and blue value stored for each pixel Stored in .jpg (JPEG) files International standard With lossy compression Lossy means not all data is stored

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Manipulating Pictures, Arrays, and Loops part 1

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  1. Manipulating Pictures, Arrays, and Loopspart 1 Georgia Institute of Technology

  2. Digital Pictures • Represented by pixels • With a red, green, and blue value stored for each pixel • Stored in .jpg (JPEG) files • International standard • With lossy compression • Lossy means not all data is stored • But what is lost isn’t that important • Compression means made smaller • Other formats for storing digital pictures are GIFF and BMP Georgia Institute of Technology

  3. Manipulating a Picture • To manipulate a picture we need to manipulate the pixels that make up the picture • Change the red, green, or blue values at the pixel • Pixel is a class that was created at Georgia Tech • Each pixel object has a red, green, and blue value

  4. What Data does a Picture Object Have? • A picture object has an array of pixel objects • That it read from the JPEG file • It knows the picture width pictureObj.getWidth() • It knows the picture height pictureObj.getHeight() • It knows how to return an array of pixels Pixel[] pixelArray = pictureObj.getPixels() Georgia Institute of Technology

  5. Picture Exercise • Create a picture in DrJava • get the pictures width, height, and number of pixels String fileName = FileChooser.pickAFile(); Picture pictureObj = new Picture(fileName); int width = pictureObj.getWidth(); System.out.println(“The picture width is “ + width); int height = pictureObj.getHeight(); System.out.println(“The picture height is “ + height); Pixel[] pixelArray = pictureObj.getPixels(); System.out.println(pixelArray.length + “ pixels”); Georgia Institute of Technology

  6. Pixel Objects • Each pixel has a red, green, and blue value • getRed(), getGreen(), getBlue() • setRed(v), setGreen(v), setBlue(v) • Each pixel knows the location it was in the picture object • getX(), get(Y) • You can also get and set the color at the pixel • getColor(), setColor(color) Georgia Institute of Technology

  7. Color Objects • There is a class defined in Java that represents color • The Color class in the package java.awt • To use the class you must either • import java.awt.Color; • Use the full name java.awt.Color • You can create a color object by giving the red, green, and blue values for it • Color colorObj = new Color(255,10,125); Georgia Institute of Technology

  8. Predefined Colors • The Color class has defined class constants for many colors • Color.red, Color.green, Color.blue, Color.black, Color.white, Color.yellow, Color.gray, Color.orange, Color.pink, Color.cyan, Color.magenta • Or you can use all uppercase names • Color.RED, Color.BLUE, Color.BLACK, … Georgia Institute of Technology

  9. Getting and Setting Pixel Colors • To get a pixel’s color as a color object Color color1 = pixelObj.getColor(); int red = color1.getRed(); int green = color1.getGreen(); int blue = color1.getBlue(); • To set a pixel’s color using a new color object red = 20; green = 30; blue = 100; Color color2 = new Color(red,green,blue); pixelObj.setColor(color2); Georgia Institute of Technology

  10. Pixel Exercise • In DrJava • Pick a file and create a picture object • Get the array of pixels from the picture object • Get the 1st pixel from the array of pixels • Pixel pixelObj = pixelArray[0]; // 0 is first one • Get the red, green, and blue value for this pixel • Get the x and y location of this pixel • Get the color of this pixel • Get the red, green, and blue values of the color Georgia Institute of Technology

  11. Changing Pixel Colors • There are two ways to change the color of a pixel in a picture • Set the red, green, and blue values individually • pixelObj.setRed(value), • pixelObj.setGreen(value), • pixelObj.setBlue(value), • Or set the color • pixelObj.setColor(colorObj) • But, you won’t see any change in the picture • Until you ask it to repaint: pictureObj.repaint(); Georgia Institute of Technology

  12. Pictures are 2-D Arrays • They have columns and rows (x and y) • You can get a pixel at a particular x and y location • Pixel pixelObj = picture.getPixel(x,y); • The columns and rows • start with index 0 • end with num -1 X Y Georgia Institute of Technology

  13. Changing a Picture Exercise > import java.awt.Color; > String fileName = "C:/intro-prog-java/mediasources/caterpillar.jpg"; > Picture pictureObj = new Picture(fileName); > pictureObj.show(); > pictureObj.getPixel(10,100).setColor(Color.black); > pictureObj.getPixel(11,100).setColor(Color.black); > pictureObj.getPixel(12,100).setColor(Color.black); > pictureObj.getPixel(13,100).setColor(Color.black); > pictureObj.getPixel(14,100).setColor(Color.black); > pictureObj.getPixel(15,100).setColor(Color.black); > pictureObj.getPixel(16,100).setColor(Color.black); > pictureObj.getPixel(17,100).setColor(Color.black); > pictureObj.getPixel(18,100).setColor(Color.black); > pictureObj.getPixel(19,100).setColor(Color.black); > pictureObj.repaint(); Georgia Institute of Technology

  14. Method to Decrease Red • Loop through all the pixels in an array of Pixel objects and change the red in each public void decreaseRed() { Pixel[] pixelArray = this.getPixels(); int value = 0; // loop through all the pixels in the array for (Pixel pixelObj : pixelArray) { // get the red value value = pixelObj.getRed(); // decrease the red value by 50% (1/2) value = value / 2; // set the red value of the current pixel to the new value pixelObj.setRed(value); } } The body of the loop is in {} Georgia Institute of Technology

  15. Decrease Red Method public void decreaseRed() { Pixel[] pixelArray = this.getPixels(); int value = 0; Pixel pixelObj = null; int index = 0; // loop through all the pixels while(index < pixelArray.length) { // get the current pixel pixelObj = pixelArray[index]; // get the red value value = pixelObj.getRed(); // decrease the red value value = value / 2; // set the pixel red pixelObj.setRed(value); // increment the index index = index + 1; } Georgia Institute of Technology

  16. Decrease Red Exercise • In DrJava • Add the method decreaseRed() to Picture.java • Before the last } which ends the class definition • Compile the method • Click the Compile All button • Test it by doing the following in the interactions pane > String fileName = "C:/intro-prog-java/mediasources/caterpillar.jpg"; > Picture picture1 = new Picture(fileName); > picture1.explore(); > picture1.decreaseRed(); > picture1.explore(); Georgia Institute of Technology

  17. Faking a Sunset • If you want to make an outdoor scene look like it happened during sunset • You might want to increase the red • But you can’t increase past 255 • Another idea is to reduce the blue and green • To emphasize the red • Try to reduce the blue and green by 30% Georgia Institute of Technology

  18. Faking a Sunset Algorithm • Reduce the blue and green by 30% • Get the array of pixels from the picture • Set up an index to start at 0 • Loop while the index is less than the length of the array • Get the pixel at the current index from the array of pixels • Set the blue value at the pixel to 0.7 times the original value • Set the green value at the pixel to 0.7 times the original value • Increment the index and go back to step 3 Georgia Institute of Technology

  19. Faking a Sunset Method /** * Method to simulate a sunset by * decreasing the green * and blue */ public void makeSunset() { Pixel[] pixelArray = this.getPixels(); Pixel pixelObj = null; int value = 0; int i = 0; // loop through all the pixels while (i < pixelArray.length) { // get the current pixel pixelObj = pixelArray[i]; // change the blue value value = pixelObj.getBlue(); pixelObj.setBlue((int) (value * 0.7)); // change the green value value = pixelObj.getGreen(); pixelObj.setGreen((int) (value * 0.7)); // increment the index i++; } } Georgia Institute of Technology

  20. Negating an Image • How would you turn a picture into a negative? • White should become black • 255,255,255 becomes 0,0,0 • Black should become white • 0,0,0 becomes 255,255,255 Georgia Institute of Technology

  21. Negate Algorithm • Subtract current value from 255 for red, green, and blue • Get the array of pixels from the picture • Declare variables to hold the current pixel and the red, green, and blue values • Loop starting an index at 0 and incrementing by 1 and loop while the index is less than the length of the array • Get the pixel at the current index from the array of pixels • Set the red value to 255 – current red value • Set the blue value to 255 – current blue value • Set the green value to 255 – current green value • Increment the index and go back to step 3 Georgia Institute of Technology

  22. Negate Method /** * Method to negate the picture */ public void negate() { Pixel[] pixelArray = this.getPixels(); Pixel pixelObj = null; int redValue, blueValue, greenValue = 0; // loop through all the pixels for (int i = 0; i < pixelArray.length; i++) { // get the current pixel pixelObj = pixelArray[i]; // get the values redValue = pixelObj.getRed(); greenValue = pixelObj.getGreen(); blueValue = pixelObj.getBlue(); // set the pixel's color pixelObj.setColor( new Color(255 - redValue, 255 - greenValue, 255 - blueValue)); } } Georgia Institute of Technology

  23. Changing to Grayscale • Grayscale ranges from black to white • The red, green, and blue values are the same • How can we change any color to gray? • What number can we use for all three values? • The intensity of the color • We can average the colors • (red + green + blue) / 3 • Example • (15 + 25 + 230) / 3 = 90 Georgia Institute of Technology

  24. Other ideas… • Create a mirror image • Create quadrants • Create lines • Change the size • Reverse the image • ….

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