cs026_7_Part3

# cs026_7_Part3 - Topic 6 Modifying Pixels in a Matrix Part...

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1 Topic 6 Modifying Pixels in a Matrix Part 3 (Rotation, Scaling) Notes adapted from Introduction to Computing and Programming with Java: A Multimedia Approach by M. Guzdial and B. Ericson, and instructor materials prepared by B. Ericson.

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2 Rotating Pictures • Sometimes we may want to rotate a picture to the right or to the left • Which way has the image of the red motorcycle been rotated here?
3 Left Rotation • To rotate an image 90 degrees to the left, we still copy all the pixels, but they go to different locations in the target • (0, 0 ) goes to ( 0 ,2) (1, 0 ) goes to ( 0 ,1) (2, 0 ) goes to ( 0 ,0) (0, 1 ) goes to ( 1 ,2) (1, 1 ) goes to ( 1 ,1) (2, 1 ) goes to ( 1 ,0) • What happens to the row values? • They go to the columns : target x = source y (2,1) (1,1) (0,1) (2,0) (1,0) (0,0) (0,1) here (0,0) here (1,1) here (1,0) here (2,1) here (2,0) here 0 1 2 0 1 0 0 1 1 2

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4 Left Rotation • What happens to the column values? ( 0 ,0) goes to (0, 2 ) ( 1 ,0) goes to (0, 1) ( 2 ,0) goes to (0, 0) ( 0 ,1) goes to (1, 2 ) ( 1 ,1) goes to (1, 1 ) ( 2 ,1) goes to (1, 0 ) target y = source width –1 – source x (2,1) (1,1) (0,1) (2,0) (1,0) (0,0) (0,1) here (0,0) here (1,1) here (1,0) here (2,1) here (2,0) here 0 1 2 0 1 0 0 1 1 2
5 Left Rotation Method • We will now write a method to copy a picture (the source picture) to the current picture (the target picture) while rotating it to the left 90 degrees • Note that the source picture itself will not be changed • The method header will be public void copyLeftRotation(Picture sourcePicture) • Algorithm: • Loop through the source x • Loop through the source y • Get the source pixel at the x and y values • Get the target pixel whose x = the source y y = (the source picture width – 1 – source x) • Copy the color from the source pixel to the target pixel

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6 Left Rotation Method public void copyLeftRotation(Picture sourcePicture) { Pixel sourcePixel = null; Pixel targetPixel = null; int targetX, targetY = 0; // loop through the columns for (int sourceX = 0; sourceX < sourcePicture.getWidth(); sourceX++) {
7 Left Rotation Method (continued) // loop through the rows for (int sourceY = 0; sourceY < sourcePicture.getHeight(); sourceY++) { // set the target pixel color to the source pixel color sourcePixel = sourcePicture.getPixel(sourceX,sourceY); targetX = sourceY; targetY = sourcePicture.getWidth() – 1 – sourceX; targetPixel = this.getPixel(targetX,targetY); targetPixel.setColor(sourcePixel.getColor()); } } }

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8 Result of Left Rotation • Here is the image in redMotorcycle.jpg, and the result of rotating it to the left 90 degrees:
9 Right Rotation • To rotate an image 90 degrees to the right: ( 0 ,0) goes to (1, 0 ) ( 1, 0) goes to (1, 1 ) ( 2 ,0) goes to (1, 2 ) ( 0 ,1) goes to (0, 0 ) ( 1 ,1) goes to (0, 1 ) ( 2, 1) goes to (0, 2 ) • What happens to the column values? • They go to the

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## This note was uploaded on 12/20/2009 for the course COMP SCI 026 taught by Professor Unknown during the Spring '07 term at UWO.

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cs026_7_Part3 - Topic 6 Modifying Pixels in a Matrix Part...

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