c# - 如何使用 LockBits 将位图中非黑色的像素着色为黄色？

Question

使用 GetPixel 和 SetPixel 很简单，但速度很慢，所以我尝试使用 LockBits。

我很久以前就用过这种方法来比较两张图片:

public static Bitmap FastComparison(Bitmap bmp1,Bitmap bmp2)
    {
       tolerancenumeric = 15;
       int tolerance = tolerancenumeric * tolerancenumeric + 
                       tolerancenumeric * tolerancenumeric + 
                       tolerancenumeric * tolerancenumeric; //dr * dr + dg * dg + db * db;
       bmp3 = new Bitmap(512,512);  
       PixelFormat pxf = PixelFormat.Format24bppRgb;
       Rectangle rect = new Rectangle(0, 0, bmp1.Width, bmp1.Height);
       BitmapData bmpData1 = bmp1.LockBits(rect, ImageLockMode.ReadWrite, pxf);
       BitmapData bmpData2 = bmp2.LockBits(rect, ImageLockMode.ReadWrite, pxf);
       BitmapData bmpData3 = bmp3.LockBits(rect, ImageLockMode.ReadWrite, pxf);

       IntPtr ptr1 = bmpData1.Scan0;
       IntPtr ptr2 = bmpData2.Scan0;
       IntPtr ptr3 = bmpData3.Scan0;

       int numBytes = bmpData1.Stride * bmp1.Height;
       byte[] rgbValues1 = new byte[numBytes];
       Marshal.Copy(ptr1, rgbValues1, 0, numBytes);
       bmp1.UnlockBits(bmpData1);

       byte[] rgbValues2 = new byte[numBytes];
       Marshal.Copy(ptr2, rgbValues2, 0, numBytes);
       bmp2.UnlockBits(bmpData2);


       for (int counter = 0; counter < rgbValues1.Length; counter += 3)
       {
          int  dr, dg, db;
          dr = (int)rgbValues2[counter] - (int)rgbValues1[counter];
          dg = (int)rgbValues2[counter + 1] - (int)rgbValues1[counter + 1];
          db = (int)rgbValues2[counter + 2] - (int)rgbValues1[counter + 2];
          int error = dr * dr + dg * dg + db * db;

          int y, x;
          y = (counter / 3) / 512;
          x = (counter - y * 512 * 3)/3;
          if ((x == 479) && (y == 474))
          {
             Byte r1, g1, b1, r2, g2, b2;
             r1 = rgbValues1[counter];
             b1 = rgbValues1[counter+1];
             g1 = rgbValues1[counter+2];
             r2 = rgbValues2[counter];
             b2 = rgbValues2[counter+1];
             g2 = rgbValues2[counter+2];
           }

           if (error < tolerance)
           {
             rgbValues1[counter] = 0; 
             rgbValues1[counter + 1] = 0;
             rgbValues1[counter + 2] = 0;
           }
         }
         Marshal.Copy(rgbValues1, 0, ptr3, numBytes);
         bmp3.UnlockBits(bmpData3);
         return bmp3;
       }

但现在我也想使用 LockBits，但使用一张图像并将所有非黑色的像素着色为黄色。

我开始了新的方法:

public Bitmap ChangeColors(Bitmap bmp1)
        {
            bmpColors = new Bitmap(512, 512);
            PixelFormat pxf = PixelFormat.Format24bppRgb;
            Rectangle rect = new Rectangle(0, 0, bmp1.Width, bmp1.Height);
            BitmapData bmpData1 = bmp1.LockBits(rect, ImageLockMode.ReadWrite, pxf);

            IntPtr ptr1 = bmpData1.Scan0;

            int numBytes = bmpData1.Stride * bmp1.Height;
            byte[] rgbValues1 = new byte[numBytes];
            Marshal.Copy(ptr1, rgbValues1, 0, numBytes);
            bmp1.UnlockBits(bmpData1);

            for (int counter = 0; counter < rgbValues1.Length; counter += 3)
            {
                int y, x;
                y = (counter / 3) / 512;
                x = (counter - y * 512 * 3) / 3;

                Byte r1, g1, b1;
                r1 = rgbValues1[counter];
                b1 = rgbValues1[counter + 1];
                g1 = rgbValues1[counter + 2];
            }

            return bmpColors;
        }

但不确定如何使位图 bmpColors 成为原始位图，但所有像素都不是黑色的黄色。

Answer 1

简单地测试字节并相应地设置它们怎么样？

Byte r1, g1, b1;
r1 = rgbValues1[counter];         // should be + 2 !!
b1 = rgbValues1[counter + 1];     // should be + 0 !!
g1 = rgbValues1[counter + 2];     // should be + 1 !!

if (r1 + b1 + g1 == 0 ) 
{
    r1 = 255;
    g1 = 255;
}

当然，这假设您可以接受纯黑色和基本黄色。

如果你需要更多的控制，你需要更多的代码，比如

if (r1 + b1 + g1 < threshold)

对于黑色阴影，对于黄色可能:

    r1 = myYellow_R;
    g1 = myYellow_G;
    b1 = myYellow_B;

顺便说一句:您需要检查那些索引；上次我查看 LockBits 数组中的数据是反转的:不是RGB，(更不用说你拥有的RBG了)但是BGR! (对于 32bpp BGRA !)

由于您使用的是旧方法，请同时确保您的像素格式没有问题；如果它是 32bpp，您需要进行一些简单的修改。