制作水印图片叠加到原图后两图跌加处出现白点问题？(急)
运行都成功的，但是在跌加好的图片上，原图和跌加上去的图片交合处会出现白色斑点，高手帮帮我啊！
源码如下：
int phWidth = imgPhoto.Width;
int phHeight = imgPhoto.Height;

//创建一个与原图尺寸相同的位图
Bitmap bmPhoto = new Bitmap(phWidth, phHeight, PixelFormat.Format24bppRgb);
bmPhoto.SetResolution(imgPhoto.HorizontalResolution, imgPhoto.VerticalResolution);

//位图装载到一个Graphics对象
Graphics grPhoto = Graphics.FromImage(bmPhoto);
//grPhoto.

//用水印BMP文件创建一个image对象
System.Drawing.Image imgWatermark = imgTezh;
int wmWidth = imgWatermark.Width;
int wmHeight = imgWatermark.Height;

//设置图片质量
grPhoto.SmoothingMode = SmoothingMode.AntiAlias;

//以原始尺寸把照片图像画到此graphics对象
grPhoto.DrawImage(
imgPhoto, // Photo Image object
new Rectangle(0, 0, phWidth, phHeight), // Rectangle structure
0, // x-coordinate of the portion of the source image to draw.
0, // y-coordinate of the portion of the source image to draw.
phWidth, // Width of the portion of the source image to draw.
phHeight, // Height of the portion of the source image to draw.
GraphicsUnit.Pixel); // Units of measure

//基于前面已修改的Bitmap创建一个新Bitmap

Bitmap bmWatermark = new Bitmap(bmPhoto);
bmWatermark.SetResolution(imgPhoto.HorizontalResolution, imgPhoto.VerticalResolution);
//Load this Bitmap into a new Graphic Object
Graphics grWatermark = Graphics.FromImage(bmWatermark);

//To achieve a transulcent watermark we will apply (2) color
//manipulations by defineing a ImageAttributes object and
//seting (2) of its properties.
ImageAttributes imageAttributes = new ImageAttributes();

//第一步是以透明色(Alpha=0, R=0, G=0, B=0)来替换背景色
//为此我们将使用一个Colormap并用它来定义一个RemapTable
ColorMap colorMap = new ColorMap();
ColorMap colorMap2 = new ColorMap();

//水印被定义为一个100%的绿色背景l
//这将是我们以transparency来查找并替换的颜色
colorMap.OldColor = Color.FromArgb(255, 255, 255, 255);
colorMap.NewColor = Color.FromArgb(0,255,255, 255);
colorMap2.OldColor = Color.FromArgb(255, 0, 0, 0);
colorMap2.NewColor = Color.FromArgb(255, 0, 0, 255);

ColorMap[] remapTable = { colorMap, colorMap2 };

imageAttributes.SetRemapTable(remapTable, ColorAdjustType.Bitmap);

int xPosOfWm = 0;
int yPosOfWm = 0;

grWatermark.DrawImage(imgWatermark,
new Rectangle(xPosOfWm, yPosOfWm, wmWidth, wmHeight), //Set the detination Position

0, // 源图的横坐标位置
0, // 源图的纵坐标位置
wmWidth, // 水印宽度
wmHeight, // 水印高度
GraphicsUnit.Pixel, // Unit of measurment
imageAttributes); //ImageAttributes Object

//以新图替换原始图
imgPhoto = bmWatermark;
grPhoto.Dispose();
grWatermark.Dispose();

[解决办法]
看看这个添加水印的
/// <summary>
/// 在图片上生成图片水印
/// </summary>
/// <param name= "Path "> 原服务器图片路径 </param>
/// <param name= "Path_syp "> 生成图片路径 </param>
/// <param name= "Path_sypf "> 水印图片路径 </param>
private void AddPicturt(string Path,string Path_syp,string Path_sypf)
{
System.Drawing.Image image=System.Drawing.Image.FromFile(Path);
System.Drawing.Image copyImage=System.Drawing.Image.FromFile(Path_sypf);
System.Drawing.Graphics g=System.Drawing.Graphics.FromImage(image);

g.DrawImage(copyImage,new System.Drawing.Rectangle(image.Width-copyImage.Width,image.Height-copyImage.Height,copyImage.Width,copyImage.Height),0,0,copyImage.Width,copyImage.Height,System.Drawing.GraphicsUnit.Pixel);

image.Save(Path_syp);
image.Dispose();
}