OpenCL in Action

I am reading the “OpenCL in Action” book and have a question on the code “simple_image.c” in Ch 6. When I run the code, I do not get the expected output PNG image, instead I simply get a white PNG image with only the top left most pixel in black color (i.e. an output image with 1 pix black, 15 pix white). Could you help me with this particular code exercise?