About the Image Processing Features in Assignment A1

The application here is an image enhancement program. It's pretty basic as such programs go, but it serves the purpose of providing a context in which to implement Undo. Five image-processing operations are provided: (0) Darken by 10%, (1) Convolve: Low-Pass, (2) Convolve: High-Pass, (3) Photonegative, and (4) RGB thresholds at 128. When the program is running, these operations are available from the "Image" menu. After an operation is performed on the image, the current image is replaced by the resulting image, and subsequent operations can be applied to this result. Thus long chains of these operations can be executed, if wanted by the user.

Knowing how the image-processing operations are implemented is not necessary for this assignment. However, here is some information about it for those interested. Three of the operations involve the use of a "lookup table" (LUT). A lookup table here is an array of 256 bytes that represent a mapping from [0, 1, ..., 255] to [0, 1, ..., 255]. The photonegative operation uses the mapping {0 -> 255, 1 -> 254, ..., 255 -> 0 }. The darken by 10% operation has its own mapping, as does the thresholding operation. Java's image module provides functionality for applying this kind of mapping to the R, G, and B color components of each pixel of a BufferedImage object. Two of the operations involve the use of Convolution filtering. This kind of operation computes each output pixel value as a weighted sum of the pixels in a (3 by 3) neighborhood. The low-pass filter is computing a weighted average, which leads to intentional blurring of the image. The high-pass filter is applying what's known as a Laplacian operator to the image and adding that result to the image thus "sharpening" it a little bit, which means making the "edges" that separate differently colored regions show up more prominently. These filtering operations are implemented in the program by instantiating java.awt.image.ConvolveOp.