How can i capture screen region while not focusing wpf app? - wpf

Question

I have a WPf application that monitors a certain region on screen keeping track of the count of pixels with certain colors.
What i want is the actual capturing of the region and reading of values to happen in another thread, but i cant seem to wrap my head around how to actuale grab the region while i focus another window.
Here is some code:
// Colors to keep track of
var fooColor = (System.Windows.Media.Color)System.Windows.Media.ColorConverter.ConvertFromString("#FF6ebfe2");
var barColor = (System.Windows.Media.Color)System.Windows.Media.ColorConverter.ConvertFromString("#FFe67e6e");
// previewWindow : Rectangle Control
var X = (int)previewWindow.PointToScreen(new System.Windows.Point(0, 0)).X;
var Y = (int)previewWindow.PointToScreen(new System.Windows.Point(0, 0)).Y;
Rectangle rect = new Rectangle(X, Y, (int)previewWindow.ActualWidth, (int)previewWindow.ActualHeight);
Bitmap bmp = new Bitmap(rect.Width, rect.Height, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
using (var screenBmp = new Bitmap(
rect.Width,
rect.Height,
System.Drawing.Imaging.PixelFormat.Format32bppArgb)
)
{
using (var bmpGraphics = Graphics.FromImage(screenBmp))
{
bmpGraphics.CopyFromScreen(X, Y, 0, 0, screenBmp.Size);
BitmapSource bmpSource = Imaging.CreateBitmapSourceFromHBitmap(
screenBmp.GetHbitmap(),
IntPtr.Zero,
Int32Rect.Empty,
BitmapSizeOptions.FromEmptyOptions());
var red = 0;
var blue = 0;
for (int i = 0; i < rect.Width; i++)
{
for (int x = 0; x < rect.Height; x++)
{
System.Windows.Media.Color color = GetPixelColor(bmpSource, i, x);
if (color == fooColor)
{
blue++;
}
else if (color == barColor)
{
red++;
}
}
}
txtbar.Text = red.ToString();
txtfoo.Text = blue.ToString();
if (red < 150)
{
ProcessBar();
}
if (blue < 150)
{
ProcessFoo();
}
}
}