我怎样才能加快这个直方图课程的速度？ [英] How can I speed up this histogram class?

问题描述

这应该计算8位灰度图像的直方图。使用1024x770测试位图，CreateTime最终在890ms左右。我怎样才能更快地实现这一目标（方式，方式）？

This is supposed to calculate the histogram of an 8-bit grayscale image. With a 1024x770 test bitmap, CreateTime ends up at around 890ms. How can I make this go (way, way) faster?

编辑：我应该提到这实际上并没有计算直方图，它只能得到值的位图。所以我真的应该问，从8位灰度图像中检索所有像素值的最快方法是什么？

I should mention that this doesn't actually compute the histogram yet, it only gets the values out of the bitmap. So I really should have asked, what is the fastest way to retrieve all pixel values from an 8-bit grayscale image?

public class Histogram {

    private static int[,] values;

    public Histogram(Bitmap b) {
        var sw = Stopwatch.StartNew();
        values = new int[b.Width, b.Height];

        for (int w = 0; w < b.Width; ++w) {
            for (int h = 0; h < b.Height; ++h) {
                values[w, h] = b.GetPixel(w, h).R;
            }
        }

        sw.Stop();
        CreateTime = (sw.ElapsedTicks /
            (double)Stopwatch.Frequency) * 1000;
    }

    public double CreateTime { get; set; }
}

推荐答案

基本直方图算法是类似于：

The basic histogram algorithm is something like:

int[] hist = new hist[256];
//at this point dont forget to initialize your vector with 0s.

for(int i = 0; i < height; ++i)
{
   for(int j = 0 ; j < widthl ++j)
   {
        hist[ image[i,j] ]++;
   }
}

算法总结了你有多少像素值0 ，有多少值= 1，依此类推。
基本思路是使用像素值作为直方图位置的索引，你将计算直方图的位置。

The algorithm sums how many pixels with value 0 you have, how many with value=1 and so on. The basic idea is to use the pixel value as the index to the position of the histogram where you will count.

我写了一个版本的算法对于C＃使用非托管代码（这很快）我不知道是否比你更快但随意采取它并测试，这是代码：

I have one version of this algorithm written for C# using unmanaged code (which is fast) I dont know if is faster than your but feel free to take it and test, here is the code:

    public void Histogram(double[] histogram, Rectangle roi)
    {
        BitmapData data = Util.SetImageToProcess(image, roi);

        if (image.PixelFormat != PixelFormat.Format8bppIndexed)
            return;

        if (histogram.Length < Util.GrayLevels)
            return;

        histogram.Initialize();
        int width = data.Width;
        int height = data.Height;
        int offset = data.Stride - width;

        unsafe
        {
            byte* ptr = (byte*)data.Scan0;

            for (int y = 0; y < height; ++y)
            {
                for (int x = 0; x < width; ++x, ++ptr)
                    histogram[ptr[0]]++;

                ptr += offset;
            }
        }
        image.UnlockBits(data);         
    }

    static public BitmapData SetImageToProcess(Bitmap image, Rectangle roi)
    {
        if (image != null)
            return image.LockBits(
                roi,
                ImageLockMode.ReadWrite,
                image.PixelFormat);

        return null;
    }

我希望我可以帮到你。

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