pyopencl内核输出黑色图像

Question

为什么图像保存后会变成黑色？我才刚开始学习opencl。在没有opencl的情况下，在纯CPU上，循环遍历矩阵并使用rgb2gray平均值公式将值存储在灰色数组中。使用windows和python 3.8

import pyopencl
import numpy as np
import imread
import matplotlib.pyplot as plt

ocl_platforms = (platform.name for platform in pyopencl.get_platforms())
print("\n".join(ocl_platforms))
# select platform
platform = pyopencl.get_platforms()[0]
# select device
device = platform.get_devices()[0]

# create context
ctx = pyopencl.Context(devices=[device])

img = imread.imread('gigapixel.jpg')

r = np.array(img[:, :, 0], dtype=np.float32)

g = np.array(img[:, :, 1], dtype=np.float32)

b = np.array(img[:, :, 2], dtype=np.float32)
gray = np.empty_like(r)
# without gpu
for i in range(r.shape[0]):
    for j in range(r.shape[1]):
        gray[i, j] = (r[i, j] + g[i, j] + b[i, j]) / 3
plt.imshow(gray)
plt.show()
# convert to uint8
gray = np.uint8(gray)
# save image
imread.imsave('gray_cpu.jpg', gray)

对于GPU，剩下的代码是

gray = np.empty_like(r)
program_source = """
__kernel void rgb2gray(__global float *r, __global float *g, __global float *b, __global 
float *gray) {
int i = get_global_id(0);
int j = get_global_id(1);
gray[i, j] = (r[i, j] + g[i, j] + b[i, j])/ 3;
}
"""
gpu_program_source = pyopencl.Program(ctx, program_source)
gpu_program = gpu_program_source.build()
program_kernel_names = gpu_program.get_info(pyopencl.program_info.KERNEL_NAMES)
print(program_kernel_names)

queue = pyopencl.CommandQueue(ctx)

r_buf = pyopencl.Buffer(ctx, pyopencl.mem_flags.READ_ONLY |             
pyopencl.mem_flags.COPY_HOST_PTR, hostbuf=r)
g_buf = pyopencl.Buffer(ctx, pyopencl.mem_flags.READ_ONLY | 
pyopencl.mem_flags.COPY_HOST_PTR, hostbuf=g)
b_buf = pyopencl.Buffer(ctx, pyopencl.mem_flags.READ_ONLY |     
pyopencl.mem_flags.COPY_HOST_PTR, hostbuf=b)
gray_buf = pyopencl.Buffer(ctx, pyopencl.mem_flags.WRITE_ONLY, r.nbytes)

gpu_program.rgb2gray(queue, r.shape, None, r_buf, g_buf, b_buf, gray_buf)

pyopencl.enqueue_copy(queue, gray, gray_buf)


plt.imshow(gray)
plt.show()

gray = np.uint8(gray)

imread.imsave('gigapixel_gray.jpg', gray)

Answer 1

如果您需要保留array[x,y]表示法，那么尝试Numba而不是PyOpenCL。Numba将Python函数的字节码转换为OpenCL内核。

PyOpenCL只是OpenCL API上的一个包装器，因此它直接编译C语言或C++语言的给定内核代码。所以你需要像这样索引：

int i = get_global_id(0);
int j = get_global_id(1);
gray[i][j] = (r[i][j] + g[i][j] + b[i][j])/ 3;

如果希望看到在任何阶段产生的错误(内核编译、缓冲区复制等)，则需要捕获PyOpenCL的异常，因为将OpenCL-错误绑定到Python。你应该这样检查他们：

try:
  your_opencl_accelerated_function()
except:
  print("Something didn't work")