使用ScaleTransform on WP7后的奇怪行为

Question

我在对方有两个图像控件，我将一些像素的alpha通道设置为零，从上一个(这是彩色的)。但在我“缩放”(宽度为ScaleTransform)之后，“边框”将在设置好的像素周围可见。这是一个截图：

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以下是代码：

        <Grid Name="grdPhotos">
            <Image Stretch="None" Source="picture_grayscale.jpg" Name="photo1" HorizontalAlignment="Left" VerticalAlignment="Top" />
            <Image Stretch="None" Source="picture.jpg" Name="photo2" MouseLeftButtonDown="photo2_MouseLeftButtonDown" HorizontalAlignment="Left" VerticalAlignment="Top" />
        </Grid>

    private void photo2_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
        var photo = photo2.Source as WriteableBitmap; // A WriteableBitmap is created before from the Source BitmapImage
        for (int x = 100; x < 200; x++)
        {
            for (int y = 100; y < 200; y++)
            {
                int index = Convert.ToInt32(photo.PixelWidth * y + x);
                if (index > 0 && index < photo.Pixels.Length)
                    SetPixelAlphaChannel(ref photo.Pixels[index], 0);
            }
        }

        var transform = new ScaleTransform { ScaleX = 2, ScaleY = 2 };
        photo1.RenderTransform = photo2.RenderTransform = transform;
    }

    public void SetPixelAlphaChannel(ref int pixel, byte value)
    {
        var color = ColorFromPixel(pixel);
        if (color.A == value)
            return;

        color.A = value;
        pixel = ColorToPixel(color);
    }

    private Color ColorFromPixel(int pixel)
    {
        var argbBytes = BitConverter.GetBytes(pixel);
        return new Color { A = argbBytes[3], R = argbBytes[2], G = argbBytes[1], B = argbBytes[0] };
    }
    private int ColorToPixel(Color color)
    {
        var argbBytes = new byte[] { color.B, color.G, color.R, color.A };
        return BitConverter.ToInt32(argbBytes, 0);
    }

为什么会这样呢？或者，如果没有这个“边框”，我如何实现缩放功能？非常感谢。

Answer 1

缩放图像时，像素值将为内插，这将导致像素在边框中--您正在观察到的结果是将透明像素与其非透明邻居进行插值的结果。不幸的是，您无法控制渲染转换的内插行为。您将不得不亲自完成此操作，可能通过WriteableBitmap。