CImage CDirect3D11RenderWindow::ScreenShot() const
{
	// Get the back buffer.
	ID3D11Texture2D* BackBuffer;
	m_SwapChain->GetBuffer( 0, __uuidof( ID3D11Texture2D ), reinterpret_cast< LPVOID* >( &BackBuffer ) );

	// Set the staging desc.
	D3D11_TEXTURE2D_DESC StagingDesc;
	BackBuffer->GetDesc( &StagingDesc );
	StagingDesc.Usage = D3D11_USAGE_STAGING;
	StagingDesc.BindFlags = 0;
	StagingDesc.CPUAccessFlags = D3D11_CPU_ACCESS_READ;

	// Create the back buffer staging texture.
	ID3D11Texture2D* BackBufferStaging;
	CDirect3D11Device::GetDevice()->CreateTexture2D( &StagingDesc, nullptr, &BackBufferStaging );

	// Copy back buffer to back buffer staging.
	CDirect3D11Device::GetDeviceContext()->CopyResource( BackBufferStaging, BackBuffer );

	// Get the size of the window.
	UInt32 Width, Height;
	GetSize( &Width, &Height );

	// Image data.
	UInt8* ImageData = new UInt8[ Width * Height * 4 ];

	// Create the image.
	D3D11_MAPPED_SUBRESOURCE Map;
	CDirect3D11Device::GetDeviceContext()->Map( BackBufferStaging, 0, D3D11_MAP_READ, 0, &Map );
	UInt8* BackBufferData = static_cast< UInt8* >( Map.pData );
	UInt8* ImageDataPtr = &ImageData[ 0 ];
	for( UInt32 y = 0; y < Height; ++y )
	{
		for( UInt32 x = 0; x < Width; ++x )
		{
			ImageDataPtr[ 4 * x + 0 ] = BackBufferData[ 4 * x + 0 ];
			ImageDataPtr[ 4 * x + 1 ] = BackBufferData[ 4 * x + 1 ];
			ImageDataPtr[ 4 * x + 2 ] = BackBufferData[ 4 * x + 2 ];
			ImageDataPtr[ 4 * x + 3 ] = 255;
		}
		BackBufferData += Map.RowPitch;
		ImageDataPtr += Width * 4;
	}
	CDirect3D11Device::GetDeviceContext()->Unmap( BackBufferStaging, 0 );

	// Release the backbuffer staging.
	BackBufferStaging->Release();

	// Create the image.
	CImage Image;
	Image.Create( Width, Height, ImageData );

	// Return the image.
	return Image;
}

I'm not well experienced actually in D3D12 but from what I saw, the read back is different than D3D11.

Is it possible to have informations about how to convert for D3D12 correctly ?

Thanks