mythma
彩色图转换为灰度图公式很简单：
Y=0.3RED+0.59GREEN+0.11 Blue

用GDI+实现的方式由两种：
1. 直接用上述公式修改象素点
2. 用ColorMatrix。

下面是用ColorMatrix实现示例：

using namespace Gdiplus;
    Image img(wszFileName);
    Graphics graphics(GetDC()->GetSafeHdc());
    ColorMatrix cm= {0.3f, 0.3f, 0.3f, 0, 0,
        0.59f,0.59f,0.59f,0, 0,
        0.11f,0.11f,0.11f,0, 0,
        0,    0,    0,    1, 0,
        0,    0,    0,    0, 1};
    ImageAttributes ia;
    ia.SetColorMatrix(&cm);

    float x = (float)img.GetWidth();
    float y = (float)img.GetHeight();
    graphics.DrawImage(&img, 
        RectF(0.0f,0.0f,x,y,
        0.0f,0.0f,x,y, 
        UnitPixel,
        &ia);

彩色图转换为灰度图公式很简单：
Y=0.3RED+0.59GREEN+0.11 Blue

用GDI+实现的方式由两种：
1. 直接用上述公式修改象素点
2. 用ColorMatrix。

下面是用ColorMatrix实现示例：

using namespace Gdiplus;
    Image img(wszFileName);
    Graphics graphics(GetDC()->GetSafeHdc());
    ColorMatrix cm= {0.3f, 0.3f, 0.3f, 0, 0,
        0.59f,0.59f,0.59f,0, 0,
        0.11f,0.11f,0.11f,0, 0,
        0,    0,    0,    1, 0,
        0,    0,    0,    0, 1};
    ImageAttributes ia;
    ia.SetColorMatrix(&cm);

    float x = (float)img.GetWidth();
    float y = (float)img.GetHeight();
    graphics.DrawImage(&img, 
        RectF(0.0f,0.0f,x,y,
        0.0f,0.0f,x,y, 
        UnitPixel,
        &ia);
 
遍历像素点，修改颜色，貌似比上面方法快

public static bool Invert0(Bitmap b) 
		{ 
			BitmapData bmData = b.LockBits(new Rectangle(0, 0, b.Width, b.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb); 
			int stride = bmData.Stride; 
			System.IntPtr Scan0 = bmData.Scan0; 
			unsafe 
			{ 
				byte * p = (byte *)(void *)Scan0; 
				int nOffset = stride - b.Width*3; 
				int nWidth = b.Width * 3; 
				int h=b.Height; 

				for(int y=0;y<h;++y) 
				{ 
					for(int x=0; x < nWidth; ++x ) 
					{ 
						p[0] = (byte)(255-p[0]); 
						++p;						 
					} 
					p += nOffset; 
				} 
			} 
			b.UnlockBits(bmData); 
			return true; 
		}

#thumbs .swiper-slide {
    opacity: 0.6;
    width: 25%;
    height: 40px;
    margin: auto 30px;
    cursor: pointer;
    filter: grayscale(100%);
}

#thumbs .swiper-slide-thumb-active {
    opacity: 1;
    filter: grayscale(0);
}

Done!

%str0='C:\Users\Administrator\Pictures\Camera Roll\'

MyYuanLaiPic = imread('C:\Users\Administrator\Pictures\Camera Roll\lena.jpg');%读取RGB格式的图像
MyFirstGrayPic = rgb2gray(MyYuanLaiPic);%用已有的函数进行RGB到灰度图像的转换

[rows , cols , colors] = size(MyYuanLaiPic);%得到原来图像的矩阵的参数
MidGrayPic = zeros(rows , cols);%用得到的参数创建一个全零的矩阵，这个矩阵用来存储用下面的方法产生的灰度图像
OldGrayPic = zeros(rows , cols);
OldGrayPic = uint8(OldGrayPic);
MidGrayPic = uint8(MidGrayPic);%将创建的全零矩阵转化为uint8格式，因为用上面的语句创建之后图像是double型的
%uint8是指0~2^8-1 = 255数据类型
for i = 1:rows 
    for j = 1:cols
        sum = 0;
        sumold = 0;
        for k = 1:colors
              sumold = sumold + MyYuanLaiPic(i , j , k) / 3;%进行转化的关键公式，sum每次都因为后面的数字而不能超过255
                switch k
                    case{1}
                            m = 0.299;
                    case{2}
                            m = 0.587;
                    case{3}
                            m = 0.114;
                end
                sum = sum + MyYuanLaiPic(i , j , k)*m;
        end
        MidGrayPic(i , j) = sum;
        OldGrayPic(i , j) = sumold;
    end
end
%imwrite(MidGrayPic , 'E:/image/matlab/DarkMouseGray.png' , 'png');
imwrite(MidGrayPic , 'DarkMouseGray.png' , 'png');
imwrite(OldGrayPic , 'OldGray.png' , 'png');
%显示原来的RGB图像
figure(1);
imshow(MyYuanLaiPic);

%显示经过系统函数运算过的灰度图像
figure(2);
imshow(MyFirstGrayPic);
%显示经过其他人设计的函数运算过的灰度图像
figure(3);
imshow(OldGrayPic);
%显示自制的转化之后的灰度图像
figure(4);
imshow(MidGrayPic);