如何使用 OpenCL 将位图转换为纯黑白

Question

我有一个 WPF - C# 项目，我正试图加快我在其中进行的图像处理；通过使用 OpenCL 和 Cloo 来实现。

我确实设法让内核工作，可以将位图更改为灰度，但出于某种原因，我制作的黑白内核只能输出全黑图像。

这是我的内核 .cl 代码：

kernel void ConvertToBlackAndWhite(read_only image2d_t sourceImage, write_only image2d_t outputImage, float threshold)
{
    const sampler_t mainSampler = CLK_NORMALIZED_COORDS_FALSE | CLK_ADDRESS_CLAMP_TO_EDGE | CLK_FILTER_LINEAR;

    int2 position = (int2)(get_global_id(0), get_global_id(1));
    float4 pixel = read_imagef(sourceImage, mainSampler, position);

    float grayValue = (0.299 * pixel.z) + (0.587 * pixel.y) + (0.114 * pixel.x); // Get Grayscale Value

    const float thresholdValue = threshold * 255.0;

    if (grayValue > thresholdValue)
    {
        const float4 white = (float4){ 255.0, 255.0, 255.0, 255.0 }; // #FFFFFF
        write_imagef(outputImage, position, white);
    }
    else
    {
        const float4 black = (float4){ 0.0, 0.0, 0.0, 255.0 }; // #000000
        write_imagef(outputImage, position, black);
    }
}

我哪里错了？

如有任何帮助或提示，我们将不胜感激。

我已经根据@ProjectPhysX 的有用建议更新了我的内核代码：

kernel void ConvertToBlackAndWhite(read_only image2d_t sourceImage, write_only image2d_t outputImage, float threshold)
{
    const sampler_t mainSampler = CLK_NORMALIZED_COORDS_FALSE | CLK_ADDRESS_CLAMP_TO_EDGE | CLK_FILTER_LINEAR;

    int2 position = (int2)(get_global_id(0), get_global_id(1));
    float4 pixel = read_imagef(sourceImage, mainSampler, position);

    float grayValue = (0.299f * pixel.z) + (0.587f * pixel.y) + (0.114f * pixel.x); // Get Grayscale Value
    if (grayValue > threshold)
    {
        const float4 white = (float4){ 1.0f, 1.0f, 1.0f, 1.0f }; // #FFFFFF
        write_imagef(outputImage, position, white);
    }
    else
    {
        const float4 black = (float4){ 0.0f, 0.0f, 0.0f, 1.0f }; // #000000
        write_imagef(outputImage, position, black);
    }
}

这是将图像添加到 OpenCL 图像内存缓冲区的 C#：

...

// Allocate OpenCL Image Memory Buffer
inputImage2DBuffer = Cl.CreateImage2D(GPUManipulation.OpenCLContext, MemFlags.CopyHostPtr | MemFlags.ReadOnly, imageFormat,
                                     (IntPtr)width, (IntPtr)height,
                                     (IntPtr)ConstantsMain.Int0, inputByteArray, out error);

...

// Allocate OpenCL image memory buffer
IMem outputImage2DBuffer = Cl.CreateImage2D(GPUManipulation.OpenCLContext, MemFlags.CopyHostPtr | MemFlags.WriteOnly, imageFormat,
                                            (IntPtr)width, (IntPtr)height, (IntPtr)ConstantsMain.Int0, outputByteArray, out error);

...

Answer 1

read_imagef returns color/alpha 范围内的值 [0.0f, 1.0f] 而不是 [0.0f, 255.0f]。这意味着您必须设置：

const float thresholdValue = threshold; // do not multiply by 255.0f here
const float4 white = (float4){ 1.0f, 1.0f, 1.0f, 1.0f }; // #FFFFFF
const float4 black = (float4){ 0.0f, 0.0f, 0.0f, 1.0f }; // #000000

之前全黑的原因是没有grayValue（在[0.0f, 1.0f]范围内）可能大于thresholdValue（在0.5f*255.0f的顺序） .

如何使用 OpenCL 将位图转换为纯黑白

How can I convert a bitmap to pure black and white with OpenCL

c#

image-processing

opencl

cloo

opencl-c