从 WINUI 应用程序中的 BitmapImage 检索特定像素颜色

Question

I'm currently starting with an application using WinUI. It's about getting the color in a specific x,y coordinates of an image. I tried to use the BitmapImage to load the image. The problem is I don't have enough info on how to access it's pixel info like color. Anyone can help on this? thanks.

Expected result is to extract color of a specific pixel in an image using BitmapImage object.

Answer 1

Use WriteableBitmap .

A WriteableBitmap provides a BitmapSource that can be modified and that doesn't use the basic file-based decoding from the WIC. You can alter images dynamically and re-render the updated image.

See Images and image brushes for more information, and

The IBuffer returned by WriteableBitmap.PixelBuffer can't be written to directly. But you can use language-specific techniques to write to the underlying pixel content in the buffer .

WriteableBitmap.PixelBuffer code snippet which comes from XAML images sample shows how to get pixel data.

using (IRandomAccessStream fileStream = await file.OpenAsync(Windows.Storage.FileAccessMode.Read)) 
{
    BitmapDecoder decoder = await BitmapDecoder.CreateAsync(fileStream); 
    // Scale image to appropriate size 
    BitmapTransform transform = new BitmapTransform() {  
        ScaledWidth = Convert.ToUInt32(Scenario4WriteableBitmap.PixelWidth), 
        ScaledHeight = Convert.ToUInt32(Scenario4WriteableBitmap.PixelHeight)
    }; 
    PixelDataProvider pixelData = await decoder.GetPixelDataAsync( 
        BitmapPixelFormat.Bgra8, // WriteableBitmap uses BGRA format 
        BitmapAlphaMode.Straight, 
        transform, 
        ExifOrientationMode.IgnoreExifOrientation, // This sample ignores Exif orientation 
        ColorManagementMode.DoNotColorManage
    ); 

    // An array containing the decoded image data, which could be modified before being displayed 
    byte[] sourcePixels = pixelData.DetachPixelData(); 

    // Open a stream to copy the image contents to the WriteableBitmap's pixel buffer 
    using (Stream stream = Scenario4WriteableBitmap.PixelBuffer.AsStream()) 
    { 
        await stream.WriteAsync(sourcePixels, 0, sourcePixels.Length); 
    }                     
}