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Nested Loops – part 2

Nested Loops – part 2. Barb Ericson Georgia Institute of Technology Nov 2009. Learning Goals. Understand at a conceptual and practical level How to mirror part of a picture How to calculate the number of times a nested loop will execute How to copy pixels from one picture to another

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Nested Loops – part 2

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  1. Nested Loops – part 2 Barb Ericson Georgia Institute of Technology Nov 2009 NestedLoops-part2

  2. Learning Goals • Understand at a conceptual and practical level • How to mirror part of a picture • How to calculate the number of times a nested loop will execute • How to copy pixels from one picture to another • How to declare, initialize and change several variables in a for loop • How to copy part of a picture to another picture Georgia Institute of Technology

  3. Mirror part of a picture • Use the explorer to figure out the part to mirror NestedLoops-part2

  4. Mirror temple method /** * Method to mirror part of the temple picture around a * vertical line at a mirror point */ public void mirrorTemple() { int mirrorPoint = 276; Pixel leftPixel = null; Pixel rightPixel = null; // loop through the rows for (int y = 27; y < 97; y++) { // loop from 13 to just before the mirror point for (int x = 13; x < mirrorPoint; x++) NestedLoops-part2

  5. Mirror temple - continued { leftPixel = getPixel(x, y); rightPixel = getPixel(mirrorPoint + (mirrorPoint - x), y); right Pixel .setColor(leftPixel .getColor()); } } } NestedLoops-part2

  6. Testing the mirrorTemple method > String fileName = "C:/intro-prog-java/mediasources/temple.jpg"; > Picture picture = new Picture(fileName); > picture.explore(); > picture.mirrorTemple(); > picture.explore(); NestedLoops-part2

  7. How many pixels were changed? • We could put print statements in the code • to see the x and y values, but that would take a long time • We can also just keep a count • And print the value of the count after the loop ends • We can calculate the number of times a loop will run using end – start + 1 = number of times • numOuter = 96 – 27 + 1 = 70 • numInner = 275 – 13 + 1 = 263 • Total for a nested loop is numInner * numOuter • 70 * 263 = 18,410 NestedLoops-part2

  8. Copying Pixels to a New Picture • Need to track the source picture x and y • And the target picture x and y • We can use a blank picture • As the target picture • Several blank pictures are available • 640x480.jpg • 7inX95in.jpg Georgia Institute of Technology

  9. Copy Picture Algorithm • Copy a picture to the 7 by 9.5 inch blank picture • Create the target picture object • Invoke the method on the target picture • Create the source picture object • 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 Georgia Institute of Technology

  10. Copy Algorithm to Code • Loop through the source pixels // loop through the columns for (int sourceX = 0, targetX = 0; sourceX < sourcePicture.getWidth(); sourceX++, targetX++) { // loop through the rows for (int sourceY = 0, targetY = 0; sourceY < sourcePicture.getHeight(); sourceY++, targetY++) { Georgia Institute of Technology

  11. Copy Algorithm to Code – Cont • Get the source and target pixels sourcePixel = sourcePicture.getPixel(sourceX,sourceY); targetPixel = this.getPixel(targetX,targetY); • Set the color of the target pixel to the color of the source pixel targetPixel.setColor(sourcePixel.getColor()); Georgia Institute of Technology

  12. Copy Method public void copyKatie() { String sourceFile = FileChooser.getMediaPath("KatieFancy.jpg"); Picture sourcePicture = new Picture(sourceFile); Pixel sourcePixel = null; Pixel targetPixel = null; // loop through the columns for (int sourceX = 0, targetX = 0; sourceX < sourcePicture.getWidth(); sourceX++, targetX++) { Georgia Institute of Technology

  13. Copy Method - Continued // loop through the rows for (int sourceY = 0, targetY = 0; sourceY < sourcePicture.getHeight(); sourceY++, targetY++) { // set the target pixel color to the source pixel color sourcePixel = sourcePicture.getPixel(sourceX,sourceY); targetPixel = this.getPixel(targetX,targetY); targetPixel.setColor(sourcePixel.getColor()); } } } Georgia Institute of Technology

  14. Trying the copyKatie Method • Create a picture object using the 7inX95in.jpg file in the mediasources directory • Picture p1 = new Picture(FileChooser.getMediaPath(“7inX95in.jpg”)); • Show the picture • p1.show(); • Invoke the method on this picture object • p1.copyKatie(); • Repaint the picture • p1.repaint(); Georgia Institute of Technology

  15. Result of copyKatie Method Georgia Institute of Technology

  16. Copying Pixels to a New Picture • 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? 0 1 0 1 0 1 2 3 0 1 2 3 Georgia Institute of Technology

  17. Copy to Position Exercise • Write a method copyRobot to copy • robot.jpg • To location • 100, 100 in 7inx95in.jpg • Test with String file = FileChooser.getMediaPath(“7inx95in.jpg”); Picture p = new Picture(file); p.copyRobot(); p.show(); Georgia Institute of Technology

  18. Cropping • We can copy just part of a picture to a new picture • Just change the start and end source x and y values to the desired values • Use pictureObj.explore() to find the x and y values • What are the x and y values to get the face of the girl in KatieFancy.jpg?

  19. Copy Face Method public void copyKatiesFace() { String sourceFile = FileChooser.getMediaPath("KatieFancy.jpg"); Picture sourcePicture = new Picture(sourceFile); Pixel sourcePixel = null; Pixel targetPixel = null; // loop through the columns for (int sourceX = 70, targetX = 100; sourceX < 135; sourceX++, targetX++) { // loop through the rows for (int sourceY = 3, targetY = 100; sourceY < 80; sourceY++, targetY++) {

  20. Copy Face Method - Continued // set the target pixel color to the source pixel color sourcePixel = sourcePicture.getPixel(sourceX,sourceY); targetPixel = this.getPixel(targetX,targetY); targetPixel.setColor(sourcePixel.getColor()); } } }

  21. Testing Copy Katie’s Face • Create a picture object • Picture p1 = new Picture(FileChooser.getMediaPath( “7inX95in.jpg”)); • Show the picture • p1.show(); • Invoke the method • p1.copyKatiesFace(); • Repaint the picture • p1.repaint();

  22. Creating a Collage • You can create a collage by copying several pictures to a blank picture • You can use the general copy method on flower1.jpg and flower2.jpg

  23. /** * Method to copy flower pictures to create a * collage. * All the flower pictures will be lined up near the * top of the current picture */ public void copyFlowersTop() { // create the flower pictures Picture flower1Picture = new Picture(FileChooser.getMediaPath( "flower1.jpg")); Picture flower2Picture = new Picture(FileChooser.getMediaPath( "flower2.jpg")); // declare the source and target pixel variables Pixel sourcePixel = null; Pixel targetPixel = null; // copy the first flower picture to the top left // corner for (int sourceX = 0, targetX = 0; sourceX < flower1Picture.getWidth(); sourceX++, targetX++) { for (int sourceY = 0, targetY = 0; sourceY < flower1Picture.getHeight(); sourceY++, targetY++) { sourcePixel = flower1Picture.getPixel(sourceX,sourceY); targetPixel = this.getPixel(targetX,targetY); targetPixel.setColor(sourcePixel.getColor()); } } Create Collage Method

  24. // copy the flower2 picture starting with x = // 100 for (int sourceX = 0, targetX = 100; sourceX < flower2Picture.getWidth(); sourceX++, targetX++) { for (int sourceY = 0, targetY = 0; sourceY < flower2Picture.getHeight(); sourceY++, targetY++) { sourcePixel = flower2Picture.getPixel(sourceX, sourceY); targetPixel = this.getPixel(targetX,targetY); targetPixel.setColor(sourcePixel.getColor()); } } // copy the flower1 negated to x = 200 flower1Picture.negate(); for (int sourceX = 0, targetX = 200; sourceX < flower1Picture.getWidth(); sourceX++, targetX++) { for (int sourceY = 0, targetY = 0; sourceY < flower1Picture.getHeight(); sourceY++, targetY++) { sourcePixel = flower1Picture.getPixel(sourceX, sourceY); targetPixel = this.getPixel(targetX,targetY); targetPixel.setColor(sourcePixel.getColor()); } } Create Collage Method - cont

  25. // clear the blue in flower 2 picture and add at // x=300 flower2Picture.clearBlue(); for (int sourceX = 0, targetX = 300; sourceX < flower2Picture.getWidth(); sourceX++, targetX++) { for (int sourceY = 0, targetY = 0; sourceY < flower2Picture.getHeight(); sourceY++, targetY++) { sourcePixel = flower2Picture.getPixel(sourceX,sourceY); targetPixel = this.getPixel(targetX,targetY); targetPixel.setColor(sourcePixel.getColor()); } } // copy the negated flower 1 to x=400 for (int sourceX = 0, targetX = 400; sourceX < flower1Picture.getWidth(); sourceX++, targetX++) { for (int sourceY = 0, targetY = 0; sourceY < flower1Picture.getHeight(); sourceY++, targetY++) { sourcePixel = flower1Picture.getPixel(sourceX, sourceY); targetPixel = this.getPixel(targetX,targetY); targetPixel.setColor(sourcePixel.getColor()); } } } Create Collage Method - cont

  26. Challenge • Create your own collage • Copy at least two different pictures to the collage • Do at least 3 different picture manipulations to the pictures • Reduce red • Negate • Clear blue • Mirror the collage

  27. Summary • To mirror part of a picture • Set the starting and ending values in the nested loop • To copy pixels from one picture to another • Keep track of the sourceX, sourceY and targetX and targetY • You can declare, initialize, and change more than one variable in a for loop for (int sourceX = 0, targetX = 0; sourceX < sourcePicture.getWidth(); sourceX++, targetX++) • You can copy just part of a picture to another picture Georgia Institute of Technology

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