How to crop SoftwareBitmap in UWP C#

Question

I took a picture using MediaCapture object and got a SoftwareBitmap. now I want to crop the image. how do I do that?

edit-this is what I tried so far:

    public async Task<SoftwareBitmap> CorpSoftwareBitmap(SoftwareBitmap original ,float scale)
    {
        int startIndex = 54;
        int M = original.PixelWidth;
        int N = original.PixelHeight;
        int m = (int)Math.Round(M * scale);
        int n = (int)Math.Round(N * scale);

        byte[] arrayOriginal;
        using (InMemoryRandomAccessStream ms = new InMemoryRandomAccessStream())
        {
            BitmapEncoder encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.BmpEncoderId,ms);
            encoder.SetSoftwareBitmap(original);
            await encoder.FlushAsync();

            arrayOriginal = new byte[ms.Size];
            await ms.ReadAsync(arrayOriginal.AsBuffer(), (uint)ms.Size, InputStreamOptions.None);
        }

        byte[] arrayCropped;
        SoftwareBitmap cropped = new SoftwareBitmap(original.BitmapPixelFormat, m, n);
        using (InMemoryRandomAccessStream ms = new InMemoryRandomAccessStream())
        {
            BitmapEncoder encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.BmpEncoderId, ms);
            encoder.SetSoftwareBitmap(cropped);
            await encoder.FlushAsync();
            arrayCropped = new byte[ms.Size];
            await ms.ReadAsync(arrayCropped.AsBuffer(), (uint)ms.Size, InputStreamOptions.None);
        }

        int tmp = startIndex + 2 * (N - n) * M + 2 * (M - m);
        for (int i=0; i<n;i++)
        {
            Array.ConstrainedCopy(arrayOriginal, tmp + 4 * M * i, arrayCropped,startIndex + m * i, m);
        }

        cropped.CopyFromBuffer(arrayCropped.AsBuffer());


        //using (InMemoryRandomAccessStream ms = new InMemoryRandomAccessStream())
        //{
        //    ms.GetInputStreamAt(0);
        //    BitmapEncoder encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.BmpEncoderId, ms);
        //    encoder.SetSoftwareBitmap(cropped);
        //    await encoder.FlushAsync();
        //    await ms.WriteAsync(arrayCropped.AsBuffer());
        //}

        return cropped;
    }

and it doesn't write arrayCropped into cropped. both ways don't work, how do I fix that?

Thanks, Mor

Answer 1

ok, this one works:

    public async Task<SoftwareBitmap> CorpSoftwareBitmap(SoftwareBitmap original, float scale=0.5f)
    {
        int startIndex = 54;//Bitmap header length
        int M = original.PixelWidth;
        int N = original.PixelHeight;
        int m = (int)Math.Round(M * scale);
        int n = (int)Math.Round(N * scale);

        byte[] arrayOriginal;
        using (InMemoryRandomAccessStream ms = new InMemoryRandomAccessStream())
        {
            BitmapEncoder encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.BmpEncoderId, ms);
            encoder.SetSoftwareBitmap(original);
            await encoder.FlushAsync();

            arrayOriginal = new byte[ms.Size];
            await ms.ReadAsync(arrayOriginal.AsBuffer(), (uint)ms.Size, InputStreamOptions.None);
        }

        byte[] arrayCropped;
        SoftwareBitmap cropped = new SoftwareBitmap(original.BitmapPixelFormat, m, n);
        using (InMemoryRandomAccessStream ms = new InMemoryRandomAccessStream())
        {
            BitmapEncoder encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.BmpEncoderId, ms);
            encoder.SetSoftwareBitmap(cropped);
            await encoder.FlushAsync();
            arrayCropped = new byte[ms.Size];
            await ms.ReadAsync(arrayCropped.AsBuffer(), (uint)ms.Size, InputStreamOptions.None);
        }

        int tmp = startIndex + 2 * (N - n) * M + 2 * (M - m);
        for (int i = 0; i < n; i++)
            Array.ConstrainedCopy(arrayOriginal, tmp + 4 * M * i, arrayCropped,4 * m * (n-1-i), 4 * m);

        cropped.Dispose();
        cropped = SoftwareBitmap.CreateCopyFromBuffer(arrayCropped.AsBuffer(), BitmapPixelFormat.Bgra8, m, n);
        return cropped;
    }

Answer 2

There're some existing extend control to do it.

For example: An ImageCropper control for the Universal Windows Platform

The source code: https://github.com/XamlBrewer/UWP-ImageCropper-/tree/master/XamlBrewer.Uwp.Controls