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Image Processing Concepts: Loading, Displaying, and Accessing Pixels

Learn how to manipulate images in Processing using PImage and PFont classes. Load and display images, access individual pixels, and work with 2D arrays for advanced image processing effects. Experiment with text effects and alignment using PFont in your projects.

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Image Processing Concepts: Loading, Displaying, and Accessing Pixels

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  1. IAT 800 Lecture 8 PImage and PFont

  2. Outline • Programming concepts • PImage • PFont IAT 800

  3. Loading Images • Loading Images • Give your project a name and save. • Place the image file in: • <processing dir>/sketchbook/<project name>/data/ • Use this code: PImage im = loadImage(“<image filename>”); IAT 800

  4. Displaying Images • image() shows your image. • image(im, 0, 0) will display your image from the last slide at the top left of the window. IAT 800

  5. Accessing Pixels • The PImage class allows you to access the RGB values of each individual pixel of the image, with the pixels[] array. • You can get the width and height of the image file using the width and height fields of PImage. IAT 800

  6. Accessing Pixels • How do we know which pixel to look for in the array? 0 1 2 3 4 0 1 2 3 IAT 800

  7. Accessing Pixels • How do we know which pixel to look for in the array? 0 1 2 3 4 0 1 2 3 0 IAT 800

  8. Accessing Pixels • How do we know which pixel to look for in the array? 0 1 2 3 4 0 1 2 3 0 1 IAT 800

  9. Accessing Pixels • How do we know which pixel to look for in the array? 0 1 2 3 4 0 1 2 3 0 1 2 3 IAT 800

  10. Accessing Pixels • Array Index • x + y*width 0 1 2 3 4 (4, 0) = 4 + 0*5 = 4 (3, 2) = 3 + 2*5 = 13 0 1 2 3 0 1 2 3 IAT 800

  11. Accessing Pixels • What would a piece of code look like that got a color from a pixel? • Let’s look at some applications of this. PImage im = loadImage(“test1.jpg”); color c1 = im.pixels[3 + 2*im.width]; // gets color at (3, 2) stroke(c1); // set our line color so we can draw with this color. IAT 800

  12. Window vs. Image • The drawing window also has a pixels[] array. • You must call loadPixels(); to get the image from the screen • You don’t need a PImage object. loadPixels(); color c2 = pixels[3 + 2*width]; // gives us the color at (3, 2) in the window. IAT 800

  13. Window vs. Image • When would we want to use both of these? • Use the Window’s pixels if you want to draw more things based on the image that’s already on the screen. • Use the Image’s pixels if you want to manipulate the pixels of the image before you draw them. IAT 800

  14. 2D Arrays • Java lets us make Arrays of Arrays, otherwise called 2D Arrays. These are very useful for accessing arrays of pixels like the ones we’ve been working with. int[][] bob = new int[3][4]; color[][] pixels2d = new color[200][200]; IAT 800

  15. 2D Arrays • Processing doesn’t provide us with a 2D array of pixels to use, so let’s develop a class that will make manipulating pixels easier. IAT 800

  16. 2D Arrays • Interestingly, 2D Arrays are just covering up a 1D array much like the pixels[] array. color[][] pixels2d = new color[20][20]; color c2 = pixels2d[3][2]; color[] pixels1d = new color[400]; color c1 = pixels1d[3 + 2*20]; Underneath, these two pieces of code do the same thing. The 2D array convention just makes it easier for us to access the array based on things like our x and y values. IAT 800

  17. PFont • PFont is the Processing class for manipulating fonts • Like PImage for images • Use PFont with • PFont loadFont() – loads a font • textFont(PFont font, int size) – sets the current font • text(String str, int x, int y) – draws a string in the current font at the current location • Also text(String str, float x, float y) IAT 800

  18. Simple example // the fonts must be located in the data directory PFont eureka = loadFont("Eureka90.vlw"); PFont zig = loadFont("Ziggurat-HTF-Black-32.vlw"); textFont(eureka, 44); text("word", 10, 30); textFont(zig, 44); text("word", 10, 60); IAT 800

  19. Use fill() to change the color of text // the fonts must be located in the data directory PFont eureka = loadFont("Eureka90.vlw"); PFont zig = loadFont("Ziggurat-HTF-Black-32.vlw"); fill( 0, 255, 0 ); textFont( eureka, 44); text( "word", 10, 30); textFont( zig, 44); fill( 255, 0, 0); text( "word", 10, 60); IAT 800

  20. textMode sets the alignment • textAlign( LEFT ); • x, y is the upper left hand corner of the text • textAlign( RIGHT ); • x, y is the upper right hand corner of the text • textAlign( CENTER ); • x, y is the upper center of the text IAT 800

  21. Producing text effects • All the transform methods apply to drawing text • That means you can translate, rotate, and scale text • Combined with draw(), this means you can move text around the screen in real time • Remember, the movement of the rocket and asteroids in our asteroids example was just translation and rotation • So you can make textual machines where text moves around the screen! IAT 800

  22. Processing example void draw( ) { image( im, mouseX-370, mouseY-210 ); color c1 = im.pixels[365 + 210 * im.width ] ; loadPixels(); c1 = pixels[ 3 + 2 * width ] ; stroke( c1 ); fill( c1 ); textAlign( LEFT ); ellipse( mouseX, mouseY, 20, 10 ); textFont( eur, 44 ); text( "Yo!", mouseX + 20, mouseY + 20 ); fill( 255, 0, 0); pushMatrix(); textAlign( RIGHT ); rotate( 0.2); textFont( zig, 44 ); text( "Yo?", mouseX, mouseY + 100 ); popMatrix(); } PImage im ; PFont eur ; PFont zig ; void setup() { size( 600, 600 ); im = loadImage( "cdshaw.96.jpg" ); for( int i = 600 ; i >= 0 ; i -= 50 ) image( im, i, i ); eur = loadFont( "Eureka90.vlw" ); zig = loadFont( "Ziggurat-HTF-Black-32.vlw" ); textFont( eur ); } IAT 800

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