如何在 Xamarin.UWP 中调整大小和减小大小（使用压缩质量值）

Question

I am trying to write a function that will resize an image and compress it using a compression quality value. I found some useful information here and here and here , but I am still quite confused.

I am using Dependency Services and have got it done for ios and Android successfully. Below is the code which I have used for ios.

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;
    }
}

I would like to replicate the same function for the dependency service in my UWP project, any help would be greatly appreciated.

This is what I currently have, but it does not work.

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;
}

Any thoughts on how I could change the code to resize as well as compress the image would be appreciated.

Answer 1

Got it figured out eventually, I used to code below to achieve this.

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;
}