绘制不同颜色的文本图片

        private Bitmap strToImage(string str)
        {
            Font f = new Font(new FontFamily("宋体"), 10, FontStyle.Regular);
            float fontSizeWidth = 96 / (72 / f.Size); // 字体实际像素宽度   
            float fontSizeHeight = 96 / (72 / f.Size); // 字体实际像素高度   
           

            //创建此大小的图片
            Bitmap bmp = new Bitmap(str.Length * (int)(fontSizeWidth), 22);
            Graphics g = Graphics.FromImage(bmp);
            int fIndex= str.IndexOf(findText);
            string startStr = str.Substring(0, fIndex);
          
            float y= (23- (int)fontSizeHeight) / 2;
            g.DrawString(startStr, f, new SolidBrush(System.Drawing.Color.Black), new PointF(fontSizeWidth / 2,y));
            float startLenth = startStr.Length * (int)(fontSizeWidth );
            g.DrawString(findText, f, new SolidBrush(System.Drawing.Color.Red), new PointF(startLenth, y));//绘制红字
            string enStr = str.Substring(fIndex + findText.Length);
            float findTxLenth = findText.Length * (int)(fontSizeWidth );
            g.DrawString(enStr, f, new SolidBrush(System.Drawing.Color.Black), new PointF(startLenth+findTxLenth , y));
            g.Save();
            g.Dispose();
            return bmp;
        }