PImage data type

A PImage object is the equivalent of an "off-stage" canvas that stores an array of pixels. We can examine and manipulate the color settings for those pixels and later render the PImage to an actual canvas.

loadImage() function

Examples:

• PImage slu = loadImage("campus4.jpg");     // must be stored in sketch directory

• PImage slu = loadImage("/Users/goldwasser/Documents/campus4.jpg");

• PImage slu = loadImage("http://business.slu.edu/uploads/2012/11/08/slu-homepage-campus4.jpg");

createImage() function

We can also create a new (blank) PImage object by using the createImage() function with a given width and height and color model. Examples are:

• PImage example = createImage(400,200,RGB);

  To create a new 400-by-200 image using RGB colors (but no alpha channel)

• PImage sample = createImage(400,200,ARGB);

  To create a new 400-by-200 image using RGB colors with alpha

• PImage sample = createImage(400,200,ALPHA);

  To create a new 400-by-200 image using grayscale color with alpha

background() function

We have previously used the background function to set the entire canvas background to a particular color. It is also possible to set the entire canvas background to a given image, as in

background(slu);

image() function

We can display a particular PImage object on our canvas, with top-left corner at (x,y) using a command of the form:

image(slu, x, y);

You can also use transformation functions such as scale and rotate to alter the canvas coordinate system before rendering an image.

Useful functions of a PImage object

For the following examples, assume our image is named with variable img.

• get(x, y);

  Returns the color of the pixel at coordinate (x,y) of the PImage.
  Example:

  color c = img.get(25,0);

• get(x, y, w, h);

  Returns a new PImage of width w and heighth which is a copy of the rectangle anchored at (x,y) in the original PImage.
  Example:

  PImage sample = img.get(25,0,100,50);

• set(x, y, c);

  Set the pixel at coordinate (x,y) of the PImage to color c.
  Example:

  img.set(100, 50, color(255,0,0));

• set(x, y, image);

  Sets the rectangle anchored at coordinate (x,y) in one PImage to be a copy of an entire other image.
  Example:

  img.set(100, 50, slu);

Additional "Bells and Whistles"

There exists functionality for many common image processing tasks (although, for the purpose of exploration, we may later develop our own low-level implementations for many of these). To demonstrate several of these, we rely on the following reference image.

• img.save(filename);

  Saves the current PImage directly to a file (typically .jpg, .tif, .png format).

• img.resize(w,h);

  Resizes an image to new width and height (scaling appropriately).
  

• img.mask(other);

  Uses the other PImage as a "mask" for the first image. The other image should use grayscale values, but those grayscale values will be treated as new alpha values for transparency in masking the first image.
  

• img.filter(...);

  has many uses:

  • img.filter(GRAY);

    Converts image to grayscale.
    

  • img.filter(INVERT);

    Converts image to "negative" color, in effect inverting the color components for each pixel
    

  • img.filter(THRESHOLD, pct);

    Converts image to black and white, depending on whether each pixel is above or below the given threshold percentage.
    

  • img.filter(BLUR, radius);

    Blurs the image using a Gaussian blur with the given radius.
    
    
    

  • img.filter(ERODE);

    Reduces the light areas.
    
    
    

  • img.filter(DILATE);

    Increases the light areas.
    
    
    

  • img.filter(POSTERIZE, num);

    For each color channel, reduces the number of distinct color values that can be used to num (for some 1 ≤ num ≤ 255)

• img.blend(...);

  blending is another multipurpose tool that allows you to compose two images (or portions thereof) on a pixel-by-pixel basis. Depending on the parameterization, it can take a (weighted) average of the two corresponding pixels, add them, subtract them, take the darker or lighter of the two, and various other forms of combination.

  See documentation for more details.