PyOpenCL 错误的输出图像

Question

我试图在图像上添加渐变 - works.CPU 和 GPU 程序应该做同样的事情。我对输出图像有疑问，因为 GPU 代码给我的图像与 CPU 代码不同，我不知道哪里出错了。我认为 CPU 代码没问题，但 GPU 不行。 Output images - 原始，cpu，gpu - 请检查我的代码。谢谢。

import pyopencl as cl
import sys
import Image
import numpy
from time import time

def gpu_gradient():

    if len(sys.argv) != 3:
        print "USAGE: " + sys.argv[0] + " <inputImageFile> <outputImageFile>"
        return 1

    # create context and command queue
    ctx = cl.create_some_context()
    queue = cl.CommandQueue(ctx)

    # load image
    im = Image.open(sys.argv[1])
    if im.mode != "RGBA":
        im = im.convert("RGBA")
    imgSize = im.size
    buffer = im.tostring() # len(buffer) = imgSize[0] * imgSize[1] * 4


    # Create ouput image object
    clImageFormat = cl.ImageFormat(cl.channel_order.RGBA, 
                                cl.channel_type.UNSIGNED_INT8)
    input_image = cl.Image(ctx,
                                cl.mem_flags.READ_ONLY | cl.mem_flags.COPY_HOST_PTR,
                                clImageFormat,
                                imgSize,
                                None,
                                buffer)
    output_image = cl.Image(ctx,
                            cl.mem_flags.WRITE_ONLY,
                            clImageFormat,
                            imgSize)

    # load the kernel source code
    kernelFile = open("gradient.cl", "r")
    kernelSrc = kernelFile.read()

    # Create OpenCL program
    program = cl.Program(ctx, kernelSrc).build()
    # Call the kernel directly
    globalWorkSize = ( imgSize[0],imgSize[1] ) 
    gpu_start_time = time()
    program.gradientcover(queue,
                            globalWorkSize,
                            None,
                            input_image,
                            output_image)

    # Read the output buffer back to the Host
    buffer = numpy.zeros(imgSize[0] * imgSize[1] * 4, numpy.uint8)
    origin = ( 0, 0, 0 )
    region = ( imgSize[0], imgSize[1], 1 )

    cl.enqueue_read_image(queue, output_image,
                        origin, region, buffer).wait()

    # Save the image to disk
    gsim = Image.fromstring("RGBA", imgSize, buffer.tostring())
    gsim.save("GPU_"+sys.argv[2])
    gpu_end_time = time()
    print("GPU Time: {0} s".format(gpu_end_time - gpu_start_time))

def cpu_gradient():
    if len(sys.argv) != 3:
        print "USAGE: " + sys.argv[0] + " <inputImageFile> <outputImageFile>"
        return 1

    gpu_start_time = time()
    im = Image.open(sys.argv[1])
    if im.mode != "RGBA":
        im = im.convert("RGBA")
    pixels = im.load()
    for i in range(im.size[0]):
        for j in range(im.size[1]):

            RGBA= pixels[i,j]
            RGBA2=RGBA[0],RGBA[1],0,0
            pixel=RGBA[0]+RGBA2[0],RGBA[1]+RGBA2[1],RGBA[2],RGBA[3]

            final_pixels=list(pixel)
            if final_pixels[0]>255: 
                final_pixels[0]=255
            elif final_pixels[1]>255:
                final_pixels[1]=255
            pixel=tuple(final_pixels)
            pixels[i,j]=pixel
    im.save("CPU_"+sys.argv[2])
    gpu_end_time = time()
    print("CPU Time: {0} s".format(gpu_end_time - gpu_start_time))
cpu_gradient()
gpu_gradient()

内核代码：

const sampler_t sampler = CLK_NORMALIZED_COORDS_FALSE | 
                          CLK_ADDRESS_CLAMP | 
                          CLK_FILTER_NEAREST;

__kernel void gradientcover(read_only image2d_t srcImg,
                              write_only image2d_t dstImg)
{

    int2 coord = (int2) (get_global_id(0), get_global_id(1));

    uint4 pixel = read_imageui(srcImg, sampler, coord);
    uint4 pixel2 = (uint4)(coord.x, coord.y,0,0);
    pixel=pixel + pixel2;
    if(pixel.x > 255) pixel.x=255;
    if(pixel.y > 255) pixel.y=255;


    // Write the output value to image
    write_imageui(dstImg, coord, pixel);
}

Answer 1

您的 CL 和 Python 代码不做同样的事情！

        RGBA= pixels[i,j]
        RGBA2=RGBA[0],RGBA[1],0,0
        pixel=RGBA[0]+RGBA2[0],RGBA[1]+RGBA2[1],RGBA[2],RGBA[3]

将 RG 分量添加到像素。

uint4 pixel = read_imageui(srcImg, sampler, coord);
uint4 pixel2 = (uint4)(coord.x, coord.y,0,0);
pixel=pixel + pixel2;

将坐标中的 X、Y 添加到像素。

这很可能是造成结果差异的原因。

假设（根据描述）你想通过坐标变暗使图像变亮，我建议 python 代码应该是：

        RGBA= pixels[i,j]
        RGBA2=i,j,0,0

相反。

PyOpenCL 错误的输出图像

PyOpenCL wrong output image

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