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/*File ImgMod02.java.java Copyright 2004, R.G.Baldwin The purpose of this program is to make it easy to experiment with the modification of pixel data in an image and to display the modified version of the image along with the original version of the image. The program extracts the pixel data from an image file into a 3D array of type: int[row][column][depth]. The first two dimensions of the array correspond to the rows and columns of pixels in the image. The third dimension always has a value of 4 and contains the following values by index value: 0 alpha 1 red 2 green 3 blue Note that these values are stored as type int rather than type unsigned byte which is the format of pixel data in the original image. This type conversion eliminates many problems involving the requirement to perform unsigned arithmetic on unsigned byte data. The program supports gif and jpg files and possibly some other file types as well. Operation: This program provides a framework that is designed to invoke another program to process the pixels extracted from an image. In other words, this program extracts the pixels and puts them in a format that is relatively easy to work with. A second program is invoked to actually process the pixels. Typical usage is as follows: java ImgMod02 ProcessingProgramName ImageFileName For test purposes, the source code includes a class definition for an image-processing program named ProgramTest. If the ImageFileName is not specified on the command line, the program will search for an image file in the current directory named junk.gif and will process it using the processing program specified by the second command-line argument. If both command-line arguments are omitted, the program will search for an image file in the current directory named junk.gif and will process it using the built-in processing program named ProgramTest. The image file must be provided by the user in all cases. However, it doesn't have to be in the current directory if a path to the file is specified on the command line. When the program is started, the original image and the processed image are displayed in a frame with the original image above the processed image. A Replot button appears at the bottom of the frame. If the user clicks the Replot button, the image-processing method is rerun, the image is reprocessed and the new version of the processed image replaces the old version. The processing program may provide a GUI for data input making it possible for the user to modify the behavior of the image-processing method each time it is run. This capability is illustrated in the built-in processing program named ProgramTest. The image-processing programming must implement the interface named ImgIntfc02. That interface declares a single method with the following signature: int[][][] processImg(int[][][] threeDPix, int imgRows, int imgCols); The first parameter is a reference to the 3D array of pixel data stored as type int. The last two parameters specify the number of rows of pixels and the number of columns of pixels in the image. The image-processing program cannot have a parameterized constructor. This is because an object of the class is instantiated by invoking the newInstance method of the class named Class on the name of the image-processing program provided as a String on the command line. This approach to object instantiation does not support parameterized constructors. If the image-processing program has a main method, it will be ignored. The processImg method receives a 3D array containing pixel data. It should make a copy of the incoming array and modify the copy rather than modifying the original. Then the program should return a reference to the modified copy of the 3D pixel array. The program also receives the width and the height of the image represented by the pixels in the 3D array. The processImg method is free to modify the values of the pixels in the array in any manner before returning the modified array. Note however that native pixel data consists of four unsigned bytes. If the modification of the pixel data produces negative values or positive value greater than 255, this should be dealt with before returning the modified pixel data. Otherwise, the returned values will simply be masked to eight bits before display, and the result of displaying those masked bits may not be as expected. There are at least two ways to deal with this situation. One way is to simply clip all negative values at zero and to clip all values greater than 255 at 255. The other way is to perform a further modification so as to map the range from -x to +y into the range from 0 to 255. There is no one correct way for all situations. When the processImg method returns, this program causes the original image and the modified image to be displayed in a frame on the screen with the original image above the modified image. If the user doesn't specify an image-processing program, this program will instantiate and use an object of the class named ProgramTest and an image file named junk.gif. The class definition for the ProgramTest class is included in this source code file. The image file named junk.gif must be provided by the user in the current directory. Just about any gif file of an appropriate size will do. Make certain that it is small enough so that two copies will fit on the screen when stacked one above the other. The processing program named ProgramTest draws a diagonal white line across the image starting at the top left corner. The program provides a dialog box that allows the user to specify the slope of the line. To change the slope, type a new slope into the text field and press the Replot button on the main graphic frame. It isn't necessary to press the Enter key after typing the new slope value into the text field, but doing so won't cause any harm. (Note that only positive slope values can be used. Entry of a negative slope value will cause an exception to be thrown.) Other than to add the white line, the image processing program named ProgramTest does not modify the image. It does draw a visible white line across transparent areas, making the pixels underneath the line non-transparent. However, it may be difficult to see the white line against the default yellow background in the frame. If the program is unable to load the image file within ten seconds, it will abort with an error message. Some operational details follow. This program reads an image file from the disk and saves it in memory under the name rawImg. Then it declares a one-dimensional array of type int of sufficient size to contain one int value for every pixel in the image. Each int value will be populated with one alpha byte and three color bytes. The name of the array is oneDPix. Then the program instantiates an object of type PixelGrabber, which associates the rawImg with the one-dimensional array of type int. Following this, the program invokes the grabPixels method on the object of type PixelGrabber to cause the pixels in the rawImg to be extracted into int values and stored in the array named oneDPix. Then the program copies the pixel values from the oneDPix array into the threeDPix array, converting them to type int in the process. The threeDPix array is passed to an image-processing program. The image-processing program returns a modified version of the 3D array of pixel data. This program then creates a new version of the oneDPix array containing the modified pixel data. It uses the createImage method of the Component class along with the constructor for the MemoryImageSource class to create a new image from the modified pixel data. The name of the new image is mo