C#中如何高性能地把图像转换成grayscale的

C#里把图片灰度化: 先是用以下代码, 能转换, 但经测试性能比较低, 在窗口中预览灰度化的采集视频, 相当卡顿, 这是因为在两重循环里大量调用GetPixel和SetPixel

private Bitmap rgb2gray(Bitmap bm)
{
//Row-wise iteration through the Bitmap
for (int y = 0; y {
for (int x = 0; x {
Color pixelColor = bm.GetPixel(x, y);
int pixelLuminance = (int)(pixelColor.R * 0.2126 + pixelColor.G * 0.7152 + pixelColor.B * 0.0722);
bm.SetPixel(x, y, Color.FromArgb(pixelLuminance, pixelLuminance, pixelLuminance));
}//for
}//for
return bm;
}//rgb2gray(Bitmap)

?

经搜索, 在http://stackoverflow.com/questions/1580130/high-speed-performance-of-image-filtering-in-c-sharp 里找到以下代码:?

public static void GrayScaleImage(Bitmap image)
{
if (image == null)
throw new ArgumentNullException("image");
// lock the bitmap.
var data = image.LockBits(
new Rectangle(0, 0, image.Width, image.Height),
ImageLockMode.ReadWrite, image.PixelFormat);
try
{
unsafe
{
// get a pointer to the data.
byte* ptr = (byte*)data.Scan0;
// loop over all the data.
for (int i = 0; i {
for (int j = 0; j {
// calculate the gray value.
byte y = (byte)(
(0.299 * ptr[2]) +
(0.587 * ptr[1]) +
(0.114 * ptr[0]));
// set the gray value.
ptr[0] = ptr[1] = ptr[2] = y;
// increment the pointer.
ptr += 3;
}
// move on to the next line.
ptr += data.Stride - data.Width * 3;
}
}
}
finally
{
// unlock the bits when done or when
// an exception has been thrown.
image.UnlockBits(data);
}
}

?

?改用以上代码, 经测试, 性能可以, 但是处理后的图片有些问题, 左边的大部分灰度化的区域有栅格, 右边有一小段区域没有灰度化. ?这当然难不倒老杨, ?老杨感觉是ptr指向的索引不正确的问题, ?参考了下其他代码(https://github.com/baobaohuang/Graphic_gray/blob/cd1d9b543762c23a8fc232e21f8de15dd810e8b2/gray/Program.cs ?, 这个也可以工作, 性能高于最初的代码,但低于上面的代码), ?修正代码如下:?

public static void GrayScaleImage(Bitmap image)
{
if (image == null)
throw new ArgumentNullException("image");
// lock the bitmap.
var data = image.LockBits(
new Rectangle(0, 0, image.Width, image.Height),
ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
try
{
unsafe
{
// get a pointer to the data.
byte* ptr = (byte*)data.Scan0;
// loop over all the data.
for (int i = 0; i {
ptr = (byte*)data.Scan0 + i*data.Stride;
for (int j = 0; j {
// calculate the gray value.
byte y = (byte)(
(0.299 * ptr[2]) +
(0.587 * ptr[1]) +
(0.114 * ptr[0]));
// set the gray value.
ptr[0] = ptr[1] = ptr[2] = y;
// increment the pointer.
ptr += 3;
}
}
}
}
finally
{
// unlock the bits when done or when
// an exception has been thrown.
image.UnlockBits(data);
}
}

?

最后测试, 以上代码效果perfect ! ?不过后来发现, 其实两段代码的处理ptr的方式都一样可以, 主要是

var data = image.LockBits(
new Rectangle(0, 0, image.Width, image.Height),
ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

?这里必须用PixelFormat.Format24bppRgb