Wpf bitmapsource copypixels

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C#

WPF

When the Bitmap is loaded with Uri (jpeg or bmp file), the array resulting from CopyPixels, does not contains the pixels values.

Uri uri = new Uri(path);
var bitmap = new BitmapImage(uri);
BitmapSource image = bitmap;
int bytesPerPixel = (int)Math.Truncate((image.Format.BitsPerPixel + 7.0) / 8.0);
int stride = image .PixelWidth * bytesPerPixel;
int len = image.PixelHeight * stride;
byte[] pixels = new byte[len];
image.CopyPixels(pixels, stride, 0);

What I have tried:

use jpeg encoder

JpegBitmapDecoder jpegDecoder = new JpegBitmapDecoder(uri, BitmapCreateOptions.PreservePixelFormat, BitmapCacheOption.OnLoad);
BitmapFrame BmpFrame = jpegDecoder.Frames[0];

try to get pixels from BmpFrame, no success again