Question

我有一个WPF应用程序，它有一个图像列表框。现在我使用BitmapImage和BitmapCacheOption.OnLoad来加载图像。问题在于，当存在大量图像时，由于图像的大小，RAM使用天空火箭。如何创建要在列表框中显示的原件缩略图？它可能必须缓存，因为我可能会在应用程序运行时删除或修改目录中的图像文件。

Answer 1

问题在于，当有大量图像时，由于图像的大小，RAM使用天空火箭。

C＃示例：http://msdn.microsoft.com/en-us/library/ms748873.aspx

// Create source
BitmapImage myBitmapImage = new BitmapImage();

// BitmapImage.UriSource must be in a BeginInit/EndInit block
myBitmapImage.BeginInit();
myBitmapImage.UriSource = new Uri(@"C:\Water Lilies.jpg");

// To save significant application memory, set the DecodePixelWidth or  
// DecodePixelHeight of the BitmapImage value of the image source to the desired 
// height or width of the rendered image. If you don't do this, the application will 
// cache the image as though it were rendered as its normal size rather then just 
// the size that is displayed.
// Note: In order to preserve aspect ratio, set DecodePixelWidth
// or DecodePixelHeight but not both.
myBitmapImage.DecodePixelWidth = 200;
myBitmapImage.EndInit();
//
//when you are ready to render the BitmapImage, do:
imageThumb.Source = myBitmapImage;

请注意DecodePixelWidth和DecodePixelHeight属性，以便以所需的缩小像素大小缓存图像。使用两者来拉伸图像以适合缩略图大小。

Answer 2

您可以使用InterpolationMode.HighQualityBicubic

创建合适的拇指位图

   Bitmap bitmap = ...
   Bitmap thumbBitmap = new System.Drawing.Bitmap(thumbWidth, thumbHeight);
   using (Graphics g = Graphics.FromImage(thumbBitmap))
   {
      g.InterpolationMode = InterpolationMode.HighQualityBicubic;
      g.DrawImage(bitmap, 0, 0, thumbWidth, thumbHeight);
   }

如果您在后台线程中创建拇指，只需将它们保存到内存流中，然后您可以在请求时懒惰地使用它来创建BitmapImage：

   _ms = new MemoryStream();
   thumbBitmap.Save(_ms, ImageFormat.Png);
   _ms.Position = 0;
   ImageLoaded = true;


    //thumb image property of this class, use in binding  
    public BitmapImage ThumbImage
    {
        get
        {
            if (_thumbImage == null && ImageLoaded)
            {
                BitmapImage bi = new BitmapImage();
                bi.BeginInit();
                bi.StreamSource = _ms;
                bi.EndInit();
                _thumbImage = bi;
            }
            return _thumbImage;
        }
    }

Answer 3

这是我不久前写的一个可能对你有帮助的方法。

byte[] IImageResizer.CreateThumbnailBytes(byte[] originalImage)
    {
        Image thumbnail = null;

        Image tempImage = Image.FromStream(new MemoryStream(originalImage));

        int desiredWidth = 160;

        int newPixelWidth = tempImage.Width;
        int newPixelHeight = tempImage.Height;

        if (newPixelWidth > desiredWidth)
        {
            float resizePercent = ((float)desiredWidth / (float)tempImage.Width);

            newPixelWidth = (int)(tempImage.Width * resizePercent) + 1;
            newPixelHeight = (int)(tempImage.Height * resizePercent) + 1;
        }

        Bitmap bitmap = new Bitmap(newPixelWidth, newPixelHeight);

        using (Graphics graphics = Graphics.FromImage((Image)bitmap))
        {
            graphics.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
            graphics.DrawImage(tempImage, 0, 0, newPixelWidth, newPixelHeight);
        }

        thumbnail = (Image)bitmap;

        MemoryStream ms = new MemoryStream();
        thumbnail.Save(ms, ImageFormat.Jpeg);

        return ms.ToArray();
    }

我传入原始图像二进制文件，并将图像大小调整为大约160px左右。

希望它有所帮助！

Answer 4

在检查MSDN之后，我没有看到任何直接的方法来执行此操作，但是您可能只需要每隔这么多像素对图像进行采样并将数据写入新图像，然后清理整个图像。

创建图像的缩略图并将其存储在缓存中

4 个答案: