Heterogeneous Computing with OpenCL

Chapter 9. OpenCL Case Study

Histogram

This chapter discusses optimizing memory-bound kernels—in this case, a histogram of 8-bit-per-pixel image data optimized into 256 histogram bins.

Keywords Example program, histogram, image, local, memory-bound, OpenCL

Introduction

This chapter discusses specific optimizations for a memory-bound kernel. The kernel we choose for this chapter is an image histogram operation. The source data for this operation is an 8-bit-per-pixel image with a target of counting into each of 256 32-bit histogram bins.

The principle of the histogram algorithm is to perform the following operation over each element of the image:

for( many input values ) {

histogram[ value ]++;

}

This algorithm performs many scattered read-modify-write ...