ForkLoop Images Assignment
Contents
Motivation
We gain experience using a parallel fork loop. Image processing often presents the opportunity for a lot of parallelism. Here we will operate on a single image, making a parallel task for each row.
Background
Revisit the Image Batch Race Condition Exercise's Background section for information on pixels and images.
HsvColor
class HsvColor
HsvImage
class HsvImage
- int width()
- int height()
- Optional<HsvColor> colorAtPixel(int x, int y)
- setColorAtPixel(int x, int y, HsvColor color)
- HsvColor[][] rows()
- HsvColor[] rowAt(int y)
PixelFiler
interface PixelFilter extends UnaryOperator<HsvColor>
Code To Investigate
Image Batch Race Condition Exercise
Image Batch Race Condition Code To Investigate
PixelFilters
Our Image Filter will apply a PixelFilter to every pixel in a specified image.
Some example pixel filters have been provided which use named classes, anonymous classes, and lambdas:
| class PixelFilters |
|---|
public class PixelFilters {
private static class HueSettingPixelFilter implements PixelFilter {
private final double hue;
public HueSettingPixelFilter(double hue) {
this.hue = hue;
}
@Override
public HsvColor apply(HsvColor src) {
double saturation = src.saturation();
double value = src.value();
return new HsvColor(hue, saturation, value);
}
}
public static PixelFilter hueSettingPixelFilterOf(double hue) {
// return new instance of named class HueSettingPixelFilter
return new HueSettingPixelFilter(hue);
}
public static PixelFilter hueAdjustingPixelFilterOf(double deltaHue) {
// return new instance of anonymous class
return new PixelFilter() {
@Override
public HsvColor apply(HsvColor src) {
double hue = src.hue();
double saturation = src.saturation();
double value = src.value();
return new HsvColor(hue + deltaHue, saturation, value);
}
};
}
public static PixelFilter saturationAdjustingPixelFilterOf(double deltaSaturation) {
// return anonymous function (also known as a lambda) with parameter type
return (HsvColor src) -> {
double hue = src.hue();
double saturation = src.saturation();
double value = src.value();
return new HsvColor(hue, saturation + deltaSaturation, value);
};
}
public static PixelFilter valueAdjustingPixelFilterOf(double deltaValue) {
// return anonymous function (also known as a lambda) without parameter type
return src -> {
double hue = src.hue();
double saturation = src.saturation();
double value = src.value();
return new HsvColor(hue, saturation, value + deltaValue);
};
}
}
|
Code To Implement
ParallelTaskPerRowImageFilter
| class: | ParallelTaskPerRowImageFilter.java |  |
| methods: | apply | |
| package: | imagefilter.exercise | |
| source folder: | student/src/main/java |
apply
method: public HsvImage apply(HsvImage src, PixelFilter pixelFilter) 
(parallel implementation required)
 Warning: When saving the result of pixelFilter.apply(), always put the result in a new array. Don't overwrite values of the source array. |
To complete this method we must return a new instance of the HsvImage class.
Nicely, HsvImage provides both:
- a constructor which takes an List<HsvColor[]> and,
- another constructor which takes an HsvColor[][].
These two constructors match up well with the two different return types of the many incantations of join_fork_loop:
where R is the return type of the TaskFunction<T, R> passed to the join_fork_loop.
What should the return type from the this TaskFunction be?
Visualization
| class: | ImageFilterApp.java | VIZ |
| package: | imagefilter.viz | |
| source folder: | student/src/main/java |
Testing Your Solution
| class: | __ParallelTaskPerRowImageFilterTestSuite.java |  |
| package: | imagefilter.exercise | |
| source folder: | testing/src/test/java |
Pledge, Acknowledgments, Citations
| file: | exercise-fork-loop-images-pledge-acknowledgments-citations.txt |
More info about the Honor Pledge
