CS 117 Assignment: Image Processing 1

Last spring break, my family went to England. One day, sitting on the London Underground after a long day of sightseeing, I noticed a perfect geeky photographic opportunity: my son, daughter, and wife were sitting across from me, wearing red, green, and blue jackets, respectively. "RGB" popped into my brain, so I snapped a quick picture.

Now, as I brood over the many ways I could ask you to modify existing images, this picture returns to my attention. Could you make the whole image negative, with whites turned to blacks, darks to lights, etc.? Could you make Sam's jacket purple without changing the rest of the picture? If so, what would happen to his eyes or lips? Could you replace his jacket with another image--perhaps the water in the left side of this picture (from San Diego's Seaworld, a few years earlier)?

The answer is surely yes: you could do all those things, and thus, I'm going to ask you to do so.

You can think of a digital image as a long array of pixels, each of which has a red value, a green value, and a blue value between 0 and 255. Suppose, for example, that you have an image that is 200 pixels wide and 100 pixels high. Pixel numbers 0 through 199 pixels in our imaginary array form the top row of the image, pixels 200-399 form the second row, etc.

The class EasyBufferedImage gives you some tools for manipulating standard image files of type jpg, gif, or png, using an array like the one described above. To get started using this class, first retrieve copies of EasyBufferedImage.java and ImageProcessorTest.java either via these links or from the /Accounts/courses/cs117/ondich/jackets/ directory. While you're at it, save copies of the pictures above: jackets.jpg and water.jpg.

Your mission is to create a class called ImageProcessor that contains a EasyBufferedImage object as a private variable. You should then write the following methods:

• public ImageProcessor( 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 )
  This shows your image by calling the show( String title, int x, int y ) method on your private image. The x and y allow you to position your image windows for convenient viewing.
• public void removeGreenAndBlue()
  Modifies your image to remove all the green and blue from your image, leaving only the red. You can do this by setting all the values in the green and blue pixel arrays to 0.
• public void negate()
  Converts the image to "negative" form (like a photographic negative). Here, you don't necessarily have to duplicate the color correspondence between a photo negative and its print. But you should modify all colors in a way that turns black into white, white into black, dark colors into light, light into dark, etc.
• public void replaceRed( Color replacementColor )
  Modifies your image by replacing all "red" pixels replaced by the specified color. There are two subtleties to this problem. First, you need to decide what it means for a pixel to be red (in terms of its RGB values). Second, if you just replace all "red" pixels with exactly the replacement color, you'll lose any detail in a red object (for example, the folds and zipper in a red jacket would disappear, replaced by a uniformly colored blob). The Color class has object methods getRed(), getGreen(), and getBlue(), which you may find useful to pull apart replacementColor. You only need to solve the first subtlety to get full credit for this problem (i.e., a single shade of purple covering the red jacket is ok), but you get major coolness bonuses and a sense of accomplishment if you solve the second issue.
• public void replaceRed( EasyBufferedImage replacementImage )
  Modifies the image so that all "red" pixels replaced by pixels taken from the replacement image. Note that the main image and the replacementImage need to have the same dimensions for this technique to produce the desired effect (replacing, for example, the red jacket with a portion of the water scene). If you are looking for an extra challenge, see if you can figure out a way to preserve some of the detail in the original image. For example, you would see water in place of the red jacket, but you could still see the folds, collar, and zipper of the jacket--kind of a jacket made out of water.

Test your program by using ImageProcessorTest.java. Comment out the portions of ImageProcessorTest.java that refer to methods that you haven't written yet so that you can test your code as you go.

Note that though I have provided you with two images to use for testing, you are welcome to use your own images. The only real restriction is that the two images you use for the replaceRed( EasyBufferedImage replacementImage ) method need to be the same size. Two images from the same digital camera with the same settings usually work fine. If not, you can use lots of kinds of software (e.g. the Paint program that comes standard with Windows) to modify the sizes of existing images.

Good luck, and have fun.