You can ow add post processing to an image before it gets used by Tesseract

TestVideo/Form1.cs

@@ -38,32 +38,28 @@ namespace TestVideo
 
             string path = AppDomain.CurrentDomain.BaseDirectory + "Screens\\Baneer.png";
 
-            tbxResult.Text = DecodeTessereactResults(testTesseract(path), Image.FromFile(path), pbxOutput);
+            tbxResult.Text = DecodeTessereactResults(testTesseract((Bitmap)Image.FromFile(path)), Image.FromFile(path), pbxOutput);
             //MessageBox.Show(DecodeTessereactResults(testTesseract(path), Image.FromFile(path), pbxOutput));
         }
         private Bitmap PrepareImage(Bitmap inputImage)
         {
-            using (Graphics g = Graphics.FromImage(inputImage))
+            for (int y = 0; y < inputImage.Height; y++)
             {
-                for (int y = 0; y < inputImage.Height;y++)
+                for (int x = 0; x < inputImage.Width; x++)
                 {
-                    for (int x = 0; x < inputImage.Width;x++)
+                    //We will apply a filter to put the image first in grayScale
-                    {
+                    //Then if the pixel is more white than black it will be fully white and same for black
-                        //We will apply a filter to put the image first in grayScale
-                        //Then if the pixel is more white than black it will be fully white and same for black
 
-                        //Grayscale = 0.299R + 0.587G + 0.114B
+                    //Grayscale = 0.299R + 0.587G + 0.114B
-                        Color color = inputImage.GetPixel(x,y);
+                    Color color = inputImage.GetPixel(x, y);
-                        int grayScaleValue = Convert.ToInt32(0.299 * (float)color.R + 0.587 * (float)color.G + 0.114 * (float)color.B);
+                    int grayScaleValue = Convert.ToInt32(0.299 * (float)color.R + 0.587 * (float)color.G + 0.114 * (float)color.B);
-                        int finalValue = 0;
+                    int finalValue = 0;
-                        if (grayScaleValue > 255 / 2)
+                    if (grayScaleValue > 255 / 2)
-                            finalValue = 255;
+                        finalValue = 255;
-
+                    inputImage.SetPixel(x, y, Color.FromArgb(finalValue, finalValue, finalValue));
-                        inputImage.SetPixel(x,y,Color.FromArgb(finalValue,finalValue,finalValue));
-                    }
                 }
             }
-
+            //inputImage.Save("C:/TEST/test.png",ImageFormat.Png);
             return inputImage;
         }
         private string DecodeTessereactResults(string tesseractResult, Image inputImage, PictureBox resultPbx)
@@ -86,7 +82,7 @@ namespace TestVideo
 
                     //Use the data
                     result += letter;
-                    g.DrawRectangle(new Pen(Brushes.Red,5),new Rectangle(position,size));
+                    g.DrawRectangle(new Pen(Brushes.Red, 5), new Rectangle(position, size));
                 }
             }
 
@@ -124,7 +120,7 @@ namespace TestVideo
             //testTesseract(screenshot);
 
             //SaveScreenshot(screenshot);
-            MessageBox.Show(testTesseract(SaveScreenshot(screenshot)));
+            MessageBox.Show(testTesseract(screenshot));
             return screenshot;
         }
         private string SaveScreenshot(Bitmap image)
@@ -143,10 +139,15 @@ namespace TestVideo
             return path;
         }
         //http://leonwoo-tech.blogspot.com/2018/06/tip-how-to-properly-setup-opencv-ocr-to.html
-        private string testTesseract(string filePath)
+        private string testTesseract(Bitmap inputBmp)
         {
             string result = "";
-            using (var image = new Image<Bgr, byte>(filePath))
+            //To use this toImage you need : NuGet\Install-Package Emgu.CV.Bitmap -Version 4.5.5.4823
+            inputBmp = PrepareImage(inputBmp);
+            Image<Bgr, byte> emguImage = inputBmp.ToImage<Bgr, byte>();
+
+            //using (var image = new Image<Bgr, byte>(inputBmp))
+            using (var image = emguImage)
             {
                 using (Tesseract tesseractOcrProvider = new Tesseract(AppDomain.CurrentDomain.BaseDirectory + "\\Data", "eng", OcrEngineMode.Default))
                 {
@@ -158,7 +159,6 @@ namespace TestVideo
             //  File.Delete(filePath);
             return result;
         }
-
         private void tmrScreenshots_Tick(object sender, EventArgs e)
         {
             //pbxInput.Image.Dispose();

TestVideo/TestVideo.csproj

@@ -104,6 +104,9 @@
     <PackageReference Include="Emgu.CV">
       <Version>4.5.5.4823</Version>
     </PackageReference>
+    <PackageReference Include="Emgu.CV.Bitmap">
+      <Version>4.5.5.4823</Version>
+    </PackageReference>
     <PackageReference Include="Emgu.CV.runtime.windows">
       <Version>4.5.5.4823</Version>
     </PackageReference>