C# 圖像從流調整大小

Question

我正在嘗試從流中調整圖像大小。 得到錯誤

值不能為空。參數名稱：編碼器

在線上

System.Drawing.Bitmap fullSizeBitmap = new System.Drawing.Bitmap(fullsizeImage, new System.Drawing.Size(width, image_height));

如何在此處添加編碼器？ 我需要它來自原始圖像

   public static FileProperty UploadImage(IFormFile file, string folderPath, string fileName, FileNote note, int image_height)
    {

        FileProperty property = new FileProperty();

        if (file.Length > 0)
        {

            MemoryStream ms = new MemoryStream();
            file.CopyTo(ms);
            var fileBytes = ms.ToArray();

            MemoryStream inputMemoryStream = new MemoryStream(fileBytes);
            System.Drawing.Image fullsizeImage = System.Drawing.Image.FromStream(inputMemoryStream);

            int width = (image_height / fullsizeImage.Height) * fullsizeImage.Width;

            System.Drawing.Bitmap fullSizeBitmap = new System.Drawing.Bitmap(fullsizeImage, new System.Drawing.Size(width, image_height));

            using (var stream = new MemoryStream())
            {
                fullSizeBitmap.Save(stream, fullSizeBitmap.RawFormat);

                using (MemoryStream memoryStream = new MemoryStream(stream.ToArray()))
                {
                    UploadFromStreamAsync(memoryStream);
                }
            }

            property.FileName = fileName;
            property.FileExtention = Path.GetExtension(fileName);
            property.FileSize = file.Length;
            property.FileType = file.ContentType;
            property.FileNote = note.ToString();
        }

        return property;
    }

Answer 1

這將調整從文件加載的圖像的大小並將其保存到另一個文件：

https://docs.microsoft.com/dotnet/api/system.drawing.image.save

using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;

var image = Image.FromFile(filename);
var bitmap = ResizeImage(image, widthNew, height.New);
bitmap.Save(filenameNew, image.RawFormat);

private Bitmap ResizeImage(Image image, int width, int height)
{
  var destRect = new Rectangle(0, 0, width, height);
  var destImage = new Bitmap(width, height);
  destImage.SetResolution(image.HorizontalResolution, image.VerticalResolution);
  using ( var graphics = Graphics.FromImage(destImage) )
  {
    graphics.CompositingMode = CompositingMode.SourceCopy;
    graphics.CompositingQuality = CompositingQuality.HighQuality;
    graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
    graphics.SmoothingMode = SmoothingMode.HighQuality;
    graphics.PixelOffsetMode = PixelOffsetMode.HighQuality;
    using ( var wrapMode = new ImageAttributes() )
    {
      wrapMode.SetWrapMode(WrapMode.TileFlipXY);
      graphics.DrawImage(image, destRect,
                         0, 0, image.Width, image.Height,
                         GraphicsUnit.Pixel, wrapMode);
    }
  }
  return destImage;
}

Answer 2

只需使用file.OpenReadStream()讀取並調整文件大小，然后將調整大小的位圖保存到MemoryStream並上傳。

而不是使用bitmap.RawFormat您可以使用以下方法獲取上傳的圖像格式：

if (file.Length > 0)
{
    using(var stream = file.OpenReadStream())
    {
        var image = Image.FromStream(stream);

        int width = (image_height / fullsizeImage.Height) * fullsizeImage.Width;        

        Bitmap fullSizeBitmap = new Bitmap(fullsizeImage, new Size(width, image_height));

        var imgFormat = GetImageFormat(file.FileName);

        using(var ms = new MemoryStream())
        {
            fullSizeBitmap.Save(ms, imgFormat);
            UploadFromStreamAsync(ms);
        }
    }
}

通過文件擴展名獲取圖片格式的方法：

public ImageFormat GetImageFormat(string fileName)
{
    var dotIndex = fileName.LastIndexOf('.');
    var ext = fileName.Substring(dotIndex, fileName.Length - dotIndex).ToLower();

    switch (ext)
    {
        case ".bmp": return ImageFormat.Bmp;
        case ".emf": return ImageFormat.Emf;
        case ".exif": return ImageFormat.Exif;
        case ".gif": return ImageFormat.Gif;
        case ".icon": return ImageFormat.Icon;
        case ".Jpg": return ImageFormat.Jpeg;
        case ".Jpeg": return ImageFormat.Jpeg;
        case ".png": return ImageFormat.Png;
        case ".tiff": return ImageFormat.Tiff;
        case ".Wmf": return ImageFormat.Wmf;
        default: throw new InvalidDataException("Format not supported");
    }
}

如果您仍然需要獲取上傳的圖像編碼器信息，請使用以下方法：

// ext: image extension
using System.Drawing.Imaging;

public static ImageCodecInfo GetEncoderInfo(string ext)
{
    return ImageCodecInfo.GetImageEncoders().SingleOrDefault(x => x.FilenameExtension.ToLower().Contains(ext));
}