使用c＃將圖像上傳到ASP.net后如何調整圖像大小？

Question

我嘗試上傳圖像並將其保存在主機上，然后立即調整其大小並將新圖像保存到主機上的其他位置。 這是我的代碼：

--------------- btnStart（）-----------------

    //1-get web path
    string path = Server.MapPath("..") + "\\images\\";
    string thumbPath = Server.MapPath("..") + "\\thumbnails\\";
    path += folder;
    thumbPath += folder;
    //2-get and check file extension
    String[] validext = { ".jpg", ".png" };
    string ext = System.IO.Path.GetExtension(UploadPicture.PostedFile.FileName);
    if (Array.IndexOf(validext, ext.ToLower()) < 0)
    {
        lblMessage.Text ="this file is not allowed";
        return;
    }
    //3-get and check file size
    long size = UploadPicture.PostedFile.ContentLength;
    size = size / 1024;
    if (size > 1300)
    {
        lblMessage.Text ="incorrect size";
        return;
    }
    //4-get file name
    string filename = System.IO.Path.GetFileName(UploadPicture.PostedFile.FileName);
    lblFileName.Text = filename;
    //5-check file exist and if (true) generate new name
    while (System.IO.File.Exists(path + "\\" + filename))
    filename = "1" + filename;

    //6-save file to server
    UploadPicture.PostedFile.SaveAs(path + filename);
    changeImageSize cis = new changeImageSize();
    Bitmap bm = new Bitmap(path + filename);

-----------結束事件--------------------
----------- changeImageSize類--------

public class changeImageSize
{
public changeImageSize() { }
/// <summary>
/// Method to resize, convert and save the image.
/// </summary>
/// <param name="image">Bitmap image.</param>
/// <param name="maxWidth">resize width.</param>
/// <param name="maxHeight">resize height.</param>
/// <param name="quality">quality setting value.</param>
/// <param name="filePath">file path.</param>      
public void Save(Bitmap image, int maxWidth, int maxHeight, int quality, string filePath)
{
    // Get the image's original width and height
    int originalWidth = image.Width;
    int originalHeight = image.Height;

    // To preserve the aspect ratio
    float ratioX = (float)maxWidth / (float)originalWidth;
    float ratioY = (float)maxHeight / (float)originalHeight;
    float ratio = Math.Min(ratioX, ratioY);

    // New width and height based on aspect ratio
    int newWidth = (int)(originalWidth * ratio);
    int newHeight = (int)(originalHeight * ratio);

    // Convert other formats (including CMYK) to RGB.
    Bitmap newImage = new Bitmap(newWidth, newHeight, PixelFormat.Format24bppRgb);

    // Draws the image in the specified size with quality mode set to HighQuality
    using (Graphics graphics = Graphics.FromImage(newImage))
    {
        graphics.CompositingQuality = CompositingQuality.HighQuality;
        graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
        graphics.SmoothingMode = SmoothingMode.HighQuality;
        graphics.DrawImage(image, 0, 0, newWidth, newHeight);
    }

    // Get an ImageCodecInfo object that represents the JPEG codec.
    ImageCodecInfo imageCodecInfo = this.GetEncoderInfo(ImageFormat.Jpeg);

    // Create an Encoder object for the Quality parameter.
    Encoder encoder = Encoder.Quality;

    // Create an EncoderParameters object. 
    EncoderParameters encoderParameters = new EncoderParameters(1);

    // Save the image as a JPEG file with quality level.
    EncoderParameter encoderParameter = new EncoderParameter(encoder, quality);
    encoderParameters.Param[0] = encoderParameter;
    newImage.Save(filePath, imageCodecInfo, encoderParameters);
}

/// <summary>
/// Method to get encoder infor for given image format.
/// </summary>
/// <param name="format">Image format</param>
/// <returns>image codec info.</returns>
private ImageCodecInfo GetEncoderInfo(ImageFormat format)
{
    return ImageCodecInfo.GetImageDecoders().SingleOrDefault(c => c.FormatID == format.Guid);
}
}

-----------結束課程--------------------

如您在btnStart（）事件代碼上看到的那樣，我想要在上載圖像后，以新的大小制作一個副本，並將其保存到另一個文件夾（縮略圖）。
但出現以下錯誤：

Answer 1

您的代碼運行良好。 只需檢查以下內容：

1）您的圖像沒有損壞。

2）嘗試指定不同的質量級別25、50、75。

3）在這種情況下，無法使用您指定的maxWidth，maxHeight。

4）檢查您的文件路徑。

編輯：

我將1920x1080圖像的質量級別設置為75，並嘗試將maxWidth和maxHeight設置為800x600、320x240。 它運作良好。

        ChangeImageSize cis = new ChangeImageSize();
        Bitmap b = new Bitmap(@"C:\Users\Alex Len Paul\Desktop\1\1920x1080.jpg");
        cis.Save(b, 320, 240, 75, @"C:\Users\Alex Len Paul\Desktop\1\1920x1080_2.jpg");

Answer 2

我認為這是因為在主機上保存了文件夾，所以您必須授予寫權限才能在主機上保存路徑。 您的代碼無法在主機中保存圖像