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C++ and OpenCL

Build

  • Use ./build.sh to build the CPU version, or ./build.sh gpu to build the GPU version on Linux using g++
  • Alternatively, use make to build the CPU version, or make GPU=1 to build to GPU version.
  • Run ./DeslantImg to process the images in the data/ directory
  • Two processed images are saved in the repositories root directory

Some notes on how to compile the demo manually and how to compile for Windows or other operating systems:

  • Build CPU implementation on Linux (OpenCV must be installed, libopencv-dev):

      g++ --std=c++11 src/cpp/main.cpp src/cpp/DeslantImgCPU.cpp `pkg-config --cflags --libs opencv` -o DeslantImg

  • If the macro USE_GPU is defined, the computation takes place on the GPU. To build CPU and GPU implementation on Linux (OpenCV and OpenCL must be installed, libopencv-dev nvidia-opencl-dev):

      g++ --std=c++11 -D USE_GPU src/cpp/main.cpp src/cpp/DeslantImgCPU.cpp src/cpp/DeslantImgGPU.cpp src/cpp/CLWrapper.cpp `pkg-config --cflags --libs opencv` -lOpenCL -o DeslantImg

  • With OpenCV4 it might be needed to specify opencv4 instead of opencv with pkg-config

  • On Windows, the easiest way is to use Microsoft Visual Studio, put all files into a C++ project, set include and library paths for OpenCV and optionally OpenCL, and finally compile and run the program

Run

Command line options of DeslantImg:

Usage: DeslantImg [params] imagein imageout 

	-?, -h, --help, --usage (value:true)
		print this message
	--bg_color (value:255)
		color to fill the gaps of the sheared image that is returned
	--lower_bound (value:-1.0)
		lower bound of shear values
	--upper_bound (value:1.0)
		upper bound of shear values

	imagein (value:-)
		path name to read the input image from (or stdin)
	imageout (value:-)
		path name to write the output image to (or stdout)

API

Call function deslantImg(img, bgcolor) with the input image (grayscale), and the background color (to fill empty image space). It returns the deslanted image computed on the CPU.

#include "DeslantImgCPU.hpp"
...

// read grayscale image
const cv::Mat img = cv::imread("data/test1.png", cv::IMREAD_GRAYSCALE);

// deslant it
const cv::Mat res = htr::deslantImg(img, 255);

// and save the result
cv::imwrite("out1.png", res);

OpenCL API

The GPU version additionally takes an instance of CLWrapper which holds all relevant information needed for OpenCL: deslantImg(img, bgcolor, clWrapper). As the construction of a CLWrapper instance takes time, it makes sense to only create one instance and use it for all future calls to deslantImg(img, bgcolor, clWrapper).

#include "DeslantImgGPU.hpp"
...

// read grayscale image
const cv::Mat img = cv::imread("data/test1.png", cv::IMREAD_GRAYSCALE);

// deslant it
htr::CLWrapper clWrapper;
const cv::Mat res = htr::deslantImg(img, 255, clWrapper);

// and save the result
cv::imwrite("out1.png", res);