Book Image

OpenCL Programming by Example

Book Image

OpenCL Programming by Example

Overview of this book

Research in parallel programming has been a mainstream topic for a decade, and will continue to be so for many decades to come. Many parallel programming standards and frameworks exist, but only take into account one type of hardware architecture. Today computing platforms come with many heterogeneous devices. OpenCL provides royalty free standard to program heterogeneous hardware. This guide offers you a compact coverage of all the major topics of OpenCL programming. It explains optimization techniques and strategies in-depth, using illustrative examples and also provides case studies from diverse fields. Beginners and advanced application developers will find this book very useful. Beginning with the discussion of the OpenCL models, this book explores their architectural view, programming interfaces and primitives. It slowly demystifies the process of identifying the data and task parallelism in diverse algorithms. It presents examples from different domains to show how the problems within different domains can be solved more efficiently using OpenCL. You will learn about parallel sorting, histogram generation, JPEG compression, linear and parabolic regression and k-nearest neighborhood, a clustering algorithm in pattern recognition. Following on from this, optimization strategies are explained with matrix multiplication examples. You will also learn how to do an interoperation of OpenGL and OpenCL. "OpenCL Programming by Example" explains OpenCL in the simplest possible language, which beginners will find it easy to understand. Developers and programmers from different domains who want to achieve acceleration for their applications will find this book very useful.
Table of Contents (18 chapters)
OpenCL Programming by Example
Credits
About the Authors
About the Reviewers
www.PacktPub.com
Preface
Index

Histogram calculation


Histogram is a graphical representation of tonal distribution of a digital image. It plots the number of pixels for each tonal value. In this example we find the histogram of each of the RGB color components in the color image.

In this section, we will discuss the histogram sample. The sample code has two parts the host code and the device code which is defined as a const char *histogram_kernel. For understanding purpose, we will discuss the OpenCL kernel code that follows. For an OpenCL application programmer most of the effort goes in writing the OpenCL kernel. The majority of the host code is that of setting up the OpenCL platform to run that kernel. We now start with the discussion of the kernel code.

Algorithm

The input image of size X height and Y width is divided into the small linear chunks of size BIN_SIZE=256. Each thread shall process 256 pixel values and compute the RGB histogram. Also the total number of threads in a work group which we have selected is 16...