ForkLoop Images Assignment

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

double hue()

double saturation()

double value()

HsvImage

class HsvImage

HsvImage(HsvColor[][] pixels)

HsvImage(List<HsvColor[]> pixels)

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>

HsvColor apply(HsvColor color)

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:

• List<R>, and
• R[]

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