如何在 Xamarin.UWP 中调整大小和减小大小（使用压缩质量值）

Question

我正在尝试编写一个函数来调整图像大小并使用压缩质量值对其进行压缩。我找到了一些有用的信息here and here and here，但我还是很困惑

我正在使用依赖服务并已成功完成 ios 和 Android。下面是我用于 ios.

的代码

iOS

public byte[] DecodeImage(byte[] imgBytes, int regWidth, int regHeight, int compressionQuality)
{
    try
    {
        NSData data = NSData.FromArray(imgBytes);
        var image = UIImage.LoadFromData(data);
        
        data = image.AsJPEG((nfloat) compressionQuality / 100);
        byte[] bytes = new byte[data.Length];
        System.Runtime.InteropServices.Marshal.Copy(data.Bytes, bytes, 0, Convert.ToInt32(data.Length));
        return bytes;
    }
    catch (Exception ex)
    {
        return null;
    }
}

我想在我的 UWP 项目中为依赖服务复制相同的功能，我们将不胜感激。

这是我目前拥有的，但它不起作用。

public async Task<byte[]> DecodeImageAsync(string fileUri, int regWidth, int regHeight, int compressionQuality)
{
    byte[] returnVal;

    StorageFile file = await StorageFile.GetFileFromPathAsync(fileUri);

    using (IRandomAccessStream stream = await file.OpenAsync(FileAccessMode.Read))
    {
        BitmapDecoder decoder = await BitmapDecoder.CreateAsync(stream); //ConfigureAwait(false).;

        var qualityNum = (float)compressionQuality / 100;
        var propertySet = new BitmapPropertySet();
        var qualityValue = new BitmapTypedValue(
            qualityNum, // Maximum quality
            Windows.Foundation.PropertyType.Single
        );
        propertySet.Add("ImageQuality", qualityValue);

        var resizedStream = new InMemoryRandomAccessStream();

        BitmapEncoder en = await BitmapEncoder.CreateForTranscodingAsync(resizedStream, decoder);
        BitmapEncoder encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.JpegEncoderId, stream,
            propertySet);


        double widthRatio = (double) regWidth / decoder.PixelWidth;
        double heightRatio = (double) regHeight / decoder.PixelHeight;

        double scaleRatio = Math.Min(widthRatio, heightRatio);

        if (regWidth == 0)
            scaleRatio = heightRatio;

        if (regHeight == 0)
            scaleRatio = widthRatio;

        uint aspectHeight = (uint) Math.Floor(decoder.PixelHeight * scaleRatio);
        uint aspectWidth = (uint) Math.Floor(decoder.PixelWidth * scaleRatio);

        encoder.BitmapTransform.InterpolationMode = BitmapInterpolationMode.Linear;

        encoder.BitmapTransform.ScaledHeight = aspectHeight;
        encoder.BitmapTransform.ScaledWidth = aspectWidth;

        returnVal = new byte[stream.Size];
        await encoder.FlushAsync();
        stream.Seek(0);
        returnVal = new byte[stream.Size];
        var dr = new DataReader(stream.GetInputStreamAt(0));
        await dr.LoadAsync((uint)stream.Size);
        dr.ReadBytes(returnVal);
    }
    return returnVal;
}

任何关于如何更改代码以调整大小以及压缩图像的想法都将不胜感激。

Answer 1

终于弄明白了，我曾经在下面编写代码来实现这个。

public async Task<byte[]> DecodeImageAsync(string fileUri, int regWidth, int regHeight, int compressionQuality)
{
    byte[] returnVal;

    try
    {
        StorageFile file = await StorageFile.GetFileFromPathAsync(fileUri);

        using (IRandomAccessStream stream = await file.OpenAsync(FileAccessMode.Read))
        {
            BitmapDecoder decoder = await BitmapDecoder.CreateAsync(stream);
            SoftwareBitmap softwareBitmap = await decoder.GetSoftwareBitmapAsync();

            var qualityNum = (float) compressionQuality / 100;
            var propertySet = new BitmapPropertySet();
            var qualityValue = new BitmapTypedValue(
                qualityNum, 
                Windows.Foundation.PropertyType.Single
            );
            propertySet.Add("ImageQuality", qualityValue);

            var resizedStream = new InMemoryRandomAccessStream();

            BitmapEncoder encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.JpegEncoderId, resizedStream,
                propertySet);
            encoder.SetSoftwareBitmap(softwareBitmap);
            
            double widthRatio = (double) regWidth / decoder.PixelWidth;
            double heightRatio = (double) regHeight / decoder.PixelHeight;

            double scaleRatio = Math.Min(widthRatio, heightRatio);

            if (regWidth == 0)
                scaleRatio = heightRatio;

            if (regHeight == 0)
                scaleRatio = widthRatio;

            uint aspectHeight = (uint) Math.Floor(decoder.PixelHeight * scaleRatio);
            uint aspectWidth = (uint) Math.Floor(decoder.PixelWidth * scaleRatio);

            encoder.BitmapTransform.InterpolationMode = BitmapInterpolationMode.Linear;
            encoder.BitmapTransform.ScaledHeight = aspectHeight;
            encoder.BitmapTransform.ScaledWidth = aspectWidth;
            
            await encoder.FlushAsync();
            resizedStream.Seek(0);
            returnVal = new byte[resizedStream.Size];
            var dr = new DataReader(resizedStream.GetInputStreamAt(0));
            await dr.LoadAsync((uint) resizedStream.Size);
            dr.ReadBytes(returnVal);
        }
    }catch (Exception ex)
    {
        return null;
    }
    return returnVal;
}

如何在 Xamarin.UWP 中调整大小和减小大小（使用压缩质量值）

How to resize and reduce size (using a compression quality value) in Xamarin.UWP

c#

xamarin

xamarin.forms

uwp

xamarin.uwp