我有一个简单的问题，但迄今为止我没有找到答案：在C# WinRT/WinMD项目中如何调整jpeg图像大小并将其保存为新的jpeg格式？
我正在开发Windows 8 Metro应用程序，用于从某个站点下载每日图像并将其显示在Live Tile上。问题是图像必须小于1024x1024且小于200kB，否则它将不会显示在Tile上：http://msdn.microsoft.com/en-us/library/windows/apps/hh465403.aspx
如果我有一张更大的图像，如何调整大小以适合Live Tile呢？我只考虑简单的调整大小，例如保持纵横比的情况下将宽度/2和高度/2。
这里的特定要求是代码必须作为Windows Runtime组件运行，因此WriteableBitmapEx库在这里无法使用 - 它仅适用于常规WinRT项目。即使有一个WriteableBitmapEx作为winmd项目的分支，但它还远未准备好。
以下是如何进行缩放和裁剪的示例，取自此处：
async private void BitmapTransformTest()
{
// hard coded image location
string filePath = "C:\\Users\\Public\\Pictures\\Sample Pictures\\fantasy-dragons-wallpaper.jpg";
StorageFile file = await StorageFile.GetFileFromPathAsync(filePath);
if (file == null)
return;
// create a stream from the file and decode the image
var fileStream = await file.OpenAsync(Windows.Storage.FileAccessMode.Read);
BitmapDecoder decoder = await BitmapDecoder.CreateAsync(fileStream);
// create a new stream and encoder for the new image
InMemoryRandomAccessStream ras = new InMemoryRandomAccessStream();
BitmapEncoder enc = await BitmapEncoder.CreateForTranscodingAsync(ras, decoder);
// convert the entire bitmap to a 100px by 100px bitmap
enc.BitmapTransform.ScaledHeight = 100;
enc.BitmapTransform.ScaledWidth = 100;
BitmapBounds bounds = new BitmapBounds();
bounds.Height = 50;
bounds.Width = 50;
bounds.X = 50;
bounds.Y = 50;
enc.BitmapTransform.Bounds = bounds;
// write out to the stream
try
{
await enc.FlushAsync();
}
catch (Exception ex)
{
string s = ex.ToString();
}
// render the stream to the screen
BitmapImage bImg = new BitmapImage();
bImg.SetSource(ras);
img.Source = bImg; // image element in xaml
}
使用更简单的代码重新调整图像大小，而不是裁剪。下面的代码将图像调整为80x80。
using (var sourceStream = await sourceFile.OpenAsync(FileAccessMode.Read))
{
BitmapDecoder decoder = await BitmapDecoder.CreateAsync(sourceStream);
BitmapTransform transform = new BitmapTransform() { ScaledHeight = 80, ScaledWidth = 80 };
PixelDataProvider pixelData = await decoder.GetPixelDataAsync(
BitmapPixelFormat.Rgba8,
BitmapAlphaMode.Straight,
transform,
ExifOrientationMode.RespectExifOrientation,
ColorManagementMode.DoNotColorManage);
using (var destinationStream = await destinationFile.OpenAsync(FileAccessMode.ReadWrite))
{
BitmapEncoder encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.PngEncoderId, destinationStream);
encoder.SetPixelData(BitmapPixelFormat.Rgba8, BitmapAlphaMode.Premultiplied, 80, 80, 96, 96, pixelData.DetachPixelData());
await encoder.FlushAsync();
}
}
与此同时，我还发现了这篇有关WinRT中图像处理的MSDN文章。其中大部分示例都只在JavaScript部分，所以我首先需要将其转换为C#。我还发现了这篇有用的StackOverflow文章，它是关于WinRT中图像处理的。
internal static async Task LoadTileImageInternalAsync(string imagePath)
{
string tileName = imagePath.GetHashedTileName();
StorageFile origFile = await ApplicationData.Current.LocalFolder.GetFileAsync(imagePath);
// open file for the new tile image file
StorageFile tileFile = await ApplicationData.Current.LocalFolder.CreateFileAsync(tileName, CreationCollisionOption.ReplaceExisting);
using (IRandomAccessStream tileStream = await tileFile.OpenAsync(FileAccessMode.ReadWrite))
{
// get width and height from the original image
IRandomAccessStreamWithContentType stream = await origFile.OpenReadAsync();
ImageProperties properties = await origFile.Properties.GetImagePropertiesAsync();
uint width = properties.Width;
uint height = properties.Height;
// get proper decoder for the input file - jpg/png/gif
BitmapDecoder decoder = await GetProperDecoder(stream, imagePath);
if (decoder == null) return; // should not happen
// get byte array of actual decoded image
PixelDataProvider data = await decoder.GetPixelDataAsync();
byte[] bytes = data.DetachPixelData();
// create encoder for saving the tile image
BitmapPropertySet propertySet = new BitmapPropertySet();
// create class representing target jpeg quality - a bit obscure, but it works
BitmapTypedValue qualityValue = new BitmapTypedValue(TargetJpegQuality, PropertyType.Single);
propertySet.Add("ImageQuality", qualityValue);
// create the target jpeg decoder
BitmapEncoder be = await BitmapEncoder.CreateAsync(BitmapEncoder.JpegEncoderId, tileStream, propertySet);
be.SetPixelData(BitmapPixelFormat.Rgba8, BitmapAlphaMode.Straight, width, height, 96.0, 96.0, bytes);
// crop the image, if it's too big
if (width > MaxImageWidth || height > MaxImageHeight)
{
BitmapBounds bounds = new BitmapBounds();
if (width > MaxImageWidth)
{
bounds.Width = MaxImageWidth;
bounds.X = (width - MaxImageWidth) / 2;
}
else bounds.Width = width;
if (height > MaxImageHeight)
{
bounds.Height = MaxImageHeight;
bounds.Y = (height - MaxImageHeight) / 2;
}
else bounds.Height = height;
be.BitmapTransform.Bounds = bounds;
}
// save the target jpg to the file
await be.FlushAsync();
}
}
private static async Task<BitmapDecoder> GetProperDecoder(IRandomAccessStreamWithContentType stream, string imagePath)
{
string ext = Path.GetExtension(imagePath);
switch (ext)
{
case ".jpg":
case ".jpeg":
return await BitmapDecoder.CreateAsync(BitmapDecoder.JpegDecoderId, stream);
case ".png":
return await BitmapDecoder.CreateAsync(BitmapDecoder.PngDecoderId, stream);
case ".gif":
return await BitmapDecoder.CreateAsync(BitmapDecoder.GifDecoderId, stream);
}
return null;
}
using (var sourceFileStream = await sourceFile.OpenAsync(Windows.Storage.FileAccessMode.Read))
using (var destFileStream = await destinationFile.OpenAsync(FileAccessMode.ReadWrite))
{
BitmapDecoder decoder = await BitmapDecoder.CreateAsync(sourceFileStream);
BitmapEncoder enc = await BitmapEncoder.CreateForTranscodingAsync(destFileStream, decoder);
enc.BitmapTransform.ScaledWidth = newWidth;
enc.BitmapTransform.ScaledHeight = newHeight;
await enc.FlushAsync();
await destFileStream.FlushAsync();
}
private async Task<BitmapImage> ByteArrayToBitmapImage(byte[] byteArray)
{
BitmapImage image = new BitmapImage();
using (InMemoryRandomAccessStream stream = new InMemoryRandomAccessStream())
{
using (DataWriter writer = new DataWriter(stream.GetOutputStreamAt(0)))
{
writer.WriteBytes((byte[])byteArray);
writer.StoreAsync().GetResults();
}
image.SetSource(stream);
}
image.DecodePixelHeight = 250;
image.DecodePixelWidth = 250;
return image;
}
using (var sourceStream = await imgeTOBytes.OpenAsync(FileAccessMode.Read))
{
BitmapDecoder decoder = await BitmapDecoder.CreateAsync(sourceStream);
double widthRatio = (double)maxWidth / decoder.OrientedPixelWidth;
double heightRatio = (double)maxHeight / decoder.OrientedPixelHeight;
double scaleRatio = Math.Min(widthRatio, heightRatio);
uint aspectHeight = (uint)Math.Floor((double)decoder.OrientedPixelHeight * scaleRatio);
uint aspectWidth = (uint)Math.Floor((double)decoder.OrientedPixelWidth * scaleRatio);
BitmapTransform transform = new BitmapTransform() { InterpolationMode = BitmapInterpolationMode.Fant, ScaledHeight = aspectHeight, ScaledWidth = aspectWidth };
PixelDataProvider pixelData = await decoder.GetPixelDataAsync(
BitmapPixelFormat.Rgba8,
BitmapAlphaMode.Premultiplied,
transform,
ExifOrientationMode.RespectExifOrientation,
ColorManagementMode.DoNotColorManage);
using (var destinationStream = await imgeTOBytes.OpenAsync(FileAccessMode.ReadWrite))
{
BitmapEncoder encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.PngEncoderId, destinationStream);
encoder.SetPixelData(BitmapPixelFormat.Rgba8, BitmapAlphaMode.Straight, aspectWidth, aspectHeight, 96, 96, pixelData.DetachPixelData());
await encoder.FlushAsync();
}
}`