CS 117 Assignment: Image Processing 2

For this assignment, we will get fancier in our ability to process images. We will now think of an image as a three-dimensional array of pixels: the first dimension corresponds to the rows, the second to the columns, and the third to the color bands.

This assignment will be due in two parts--part A on Friday 2/11 and part B on Wednesday 2/16. See the bottom of this page for details.

We will again use the EasyBufferedImage class, which gives us some of the basic tools that we need. Make sure to retrieve a new copy of EasyBufferedImage from the /Accounts/courses/cs117/ondich directory. While you're at it, grab a copy of either jackets.jpg or water.jpg, or obtain your own image instead if you like: you can use your picture from the Carleton directory or you can take your own picture with a digital camera.

Your mission is to create a class called ImageMultiProcessor that contains an EasyBufferedImage object as a private variable. This class will be similar in structure to the ImageProcessor class that you wrote for the last assignment, but with a different set of methods:

• public ImageMultiProcessor(String filename) throws IOException
  This is the constructor. The string is the source image filename.
• public void show(String title)
  This shows your image by calling the show(String title) method on your private image.
• public void show(String title, int x, int y)
  This shows your image by calling the show(String title, int x, int y) method on your private image.
• public boolean scale(double scaling)
  Scales your image. If scaling is 2, for example, your image should double in size. Likewise, if scaling is 0.25, your image should be 1/4 the size of the original. If scaling factor is less than or equal to 0, make no changes to the image and return false. Otherwise, return true.
• public boolean crop(int rowStart, int rowStop, int colStart, int colStop)
  Crops your image. Extracts only those pixels from pixels rowStart through rowStop and colStart through colStop. If any of the parameters are out of range for your image, leave the image unchanged and return false. Otherwise, return true.
• public void gray()
  Converts the image to gray. A gray image has only one color band instead of three. With EasyBufferedImage, you can construct a gray image with a 2-dimensional array consisting of rows and columns. To make your image gray, constuct a new image by averaging together all the color values for each pixel.
• public boolean circleCrop(int centerRow, int centerCol, int radius)
  Crops the image to a circular shaped portion of the original with a center at centerRow and centerCol and a radius of radius. Since the image itself must still be rectangular to fit inside a window, make the background of the rest of the image white. See example below. If centerRow, centerCol, radius, or some combination thereof are invalid, return false. Otherwise, return true.

• public boolean blur(int radius)
  Blurs an image. For each pixel, average all of the pixels within a circle centered at that pixel and with a radius as given. Make sure to put all of your results in a new array, instead of overwriting your original as you go; otherwise, your blurred pixels will cascade on top of each other.
• public boolean dither()
  Dithering is a technique used when you want to print a gray picture in a place such as a newspaper where no shades are available. Instead, you need to use individual pixels of black and white to simulate shades of gray. The popular Floyd-Steinberg algorithm for dithering is as follows:
  • Loop over all pixels, running across one row at a time.
  • For each pixel: if its value is larger than 128, set it to 255 (pure white). Otherwise, set it to 0 (pure black). Record the "error", which is the old value of this pixel minus the new one.
  • This "error" represents how much blackness we have added to this pixel. Distribute this blackness to adjacent pixels as follows:
  1. Add 7/16 of the error to the pixel immediately to the right ("east").
  2. Add 3/16 of the error to the pixel immediately diagonally to the bottom left ("southwest").
  3. Add 5/16 of the error to the pixel immediately below ("south").
  4. Add 1/16 of the error to the pixel immediately diagonally to the bottom right ("souhteast").
  • Any error to be distributed to pixels that are out of range should be ignored.

  Dithering should only be done on gray images, so return false if the image isn't gray already.

  
• public boolean overlay(ImageMultiProcessor overlayImage, int row, int col)
  Overlays a smaller overlayImage onto the image, as in the example below. If overlayImage can't be placed on the image (perhaps because it is too large or row or col are not valid), return false. Otherwise, return true.

Test your program by writing ImageMultiProcessorTest.java. Check the return values from your methods, and print out text indicating whether or not your methods were successful.

Assignment A (due Friday, 2/11, 5:00 PM)

Assignment A consists of getting the constructor, the show methods, and the crop method working, and is due on Friday. You and your partner should submit ImageMultiProcessor and ImageMultiProcessorTest, along with any associated images, in a directory called image2a

Assignment B (due Wednesday, 2/16, 5:00 PM)

Start early, have fun, and let me know if you need help.