SimpleImage Reference

Basic SimpleImage Functions

The simple CS106AP "SimpleImage" code provides basic digital image processing code for you to call.

• 1. Create image variable from filename. Reads the image data into memory, returning a image reference to store in a variable.
  image = SimpleImage(filename)
• 2. loop 'pixel' variable over all the pixels in the image
  

  for pixel in image:
      # use pixel in here
      pixel.red = 0
  

• 3. Access data in a pixel
• Each pixel has properties accessed with dots:
• pixel.red pixel.green pixel.blue # the 3 color values (read/write)
  e.g. pixel.red = 0 # set red value to 0
  e.g. pixel.red = pixel.red // 2 # halve red red value
• pixel.x pixel.y # the x,y coord of the pixel
• 4. Display the image - return the image, and our calling/framework code puts it on screen for you
  return image
• The red/green/blue values are stored in the image as int values in the range 0..255
• Values outside that range are changed to be 0..255 within the image:
  -Setting a value to a float like 3.5 is changed to int 3 internally
  -Setting a value larger than 255 is changed to 255 internally
  -Setting a value less than 0 is changed to 0 internally

Advanced SimpleImage Functions

• 1. Access image size: image has .width and .height attributes
  image.width
• 2. Create a blank/white image, here width 200 height 100

    image = SimpleImage.blank(200, 100)
  

• By default the image is white, every pixel (255, 255, 255). An optional third argument can specify a color for the whole image of 'black', 'red', 'green', 'blue' or 'white:

    image = SimpleImage.blank(200, 100, 'black')
  

  
  Here is an older syntax to create a blank/white image that also works:
  image = SimpleImage('', width=200, height=100)
  width and height numbers should be integers
• 3. Access 1 pixel by its x,y coordinates: image.get_pixel(x, y)
  x=0 is the left column, growing toward the right
  y=0 is the top row, growing towards the bottom
  Here accessing pixel at x 10 and y 20:
  pixel = image.get_pixel(10, 20)
• x value must be in the range 0..width-1 (inclusive)
• y value must be in the range 0..height-1 (inclusive)
• x and y numbers should be integers

Range Loop

The "foreach" above is the easiest way to loop over all the pixels. However sometimes you want to write loops to access pixels by their x,y coordinates. Here is the canonical nested range loops to access all the pixels in an image. This loop does the top row (y=0), then the next row (y=1) and so on.

def example(filename):
    image = SimpleImage(filename)
    for y in range(image.height):
        fox x in range(image.width):
            pixel = image.get_pixel(x, y)
            # do something with pixel
            pixel.red = pixel.red // 2
    return image