pdf转图片，结果图片会变小

Question

结果：图片没有一比一比例转换，怎么回事？网上的代码是C#版本，被我改成了vc版本， 不知道C#的是不是也有同样的情况.C#的代码为：
//将PDF文档转换为图片的方法        ///因为大多数的参数都有默认值startPageNum默认值为1，endPageNum默认值为总页数        /// imageFormat默认值为aImageFormat.Jpeg，resolution默认值为1        ///</summary>        ///<param name="pdfInputPath">PDF文件路径</param>        ///<param name="imageOutputPath">图片输出路径</param>        ///<param name="imageName">图片的名字，不需要带扩展名</param>        ///<param name="startPageNum">从PDF文档的第几页开始转换默认值为1</param>        ///<param name="endPageNum">从PDF文档的第几页开始停止转换，默认值为PDF总页数</param>        ///<param name="imageFormat">设置所需图片格式</param>        ///<param name="resolution">设置图片的分辨率，数字越大越清晰，默认值为1</param>        public static void ConvertPDF2Image(stringpdfInputPath,string imageOutputPath,            string imageName, intstartPageNum, int endPageNum, ImageFormat imageFormat, doubleresolution)        {           Acrobat.CAcroPDDoc pdfDoc =null;           Acrobat.CAcroPDPage pdfPage =null;           Acrobat.CAcroRect pdfRect =null;           Acrobat.CAcroPoint pdfPoint =null;            // Create the document (Can only create the AcroExch.PDDocobject using late-binding)            // Note using VisualBasic helper functions, have to addreference to DLL           pdfDoc = (Acrobat.CAcroPDDoc)Microsoft.VisualBasic.Interaction.CreateObject("AcroExch.PDDoc","");            // validateparameter            if (!pdfDoc.Open(pdfInputPath)) {throw new FileNotFoundException(); }            if (!Directory.Exists(imageOutputPath)){Directory.CreateDirectory(imageOutputPath);}            if (startPageNum <= 0) { startPageNum = 1; }            if (endPageNum > pdfDoc.GetNumPages() ||endPageNum <= 0) { endPageNum = pdfDoc.GetNumPages(); }            if (startPageNum > endPageNum) {int tempPageNum = startPageNum; startPageNum =endPageNum; endPageNum = startPageNum; }            if (imageFormat == null){ imageFormat = ImageFormat.Bmp; }            if (resolution <= 0) { resolution =1; }            // start to convert each page            for (int i =startPageNum; i <= endPageNum; i++)            {                pdfPage = (Acrobat.CAcroPDPage)pdfDoc.AcquirePage(i- 1);               pdfPoint = (Acrobat.CAcroPoint)pdfPage.GetSize();               pdfRect = (Acrobat.CAcroRect)Microsoft.VisualBasic.Interaction.CreateObject("AcroExch.Rect","");                int imgWidth = (int)((double)pdfPoint.x * resolution);               int imgHeight = (int)((double)pdfPoint.y * resolution);               pdfRect.Left = 0;               pdfRect.right = (short)imgWidth;               pdfRect.Top = 0;                pdfRect.bottom = (short)imgHeight;               // Render to clipboard, scaled by 100 percent(ie. original size)               // Even though we want a smaller image, betterfor us to scale in .NET               // than Acrobat as it would greek out smalltext               pdfPage.CopyToClipboard(pdfRect, 0, 0, (short)(100* resolution));               IDataObject clipboardData =Clipboard.GetDataObject();               if (clipboardData.GetDataPresent(DataFormats.Bitmap))               {                   Bitmap pdfBitmap = (Bitmap)clipboardData.GetData(DataFormats.Bitmap);                   pdfBitmap.Save(Path.Combine(imageOutputPath,imageName) + i.ToString() +"." +imageFormat.ToString(), imageFormat);                   pdfBitmap.Dispose();               }               // Application.DoEvents();            }           pdfDoc.Close();            Marshal.ReleaseComObject(pdfPage);            Marshal.ReleaseComObject(pdfRect);            Marshal.ReleaseComObject(pdfDoc);            Marshal.ReleaseComObject(pdfPoint);        } 
没有按照一比一比例转换