diff --git a/filter.c b/filter.c
index 730984e..581933a 100644
--- a/filter.c
+++ b/filter.c
@@ -7,7 +7,7 @@
 int main(int argc, char *argv[])
 {
     // Define allowable filters
-    char *filters = "bgrs";
+    char *filters = "bgrsi";
 
     // Get filter flag and check validity
     char filter = getopt(argc, argv, filters);
@@ -119,6 +119,12 @@ int main(int argc, char *argv[])
         case 's':
             sepia(height, width, image);
             break;
+
+        //invert
+        case 'i':
+            invert(height,width,image);
+            break;
+        
     }
 
     // Write outfile's BITMAPFILEHEADER
diff --git a/filter.exe b/filter.exe
index e59f119..0af448e 100644
Binary files a/filter.exe and b/filter.exe differ
diff --git a/helpers.c b/helpers.c
index b5b9258..8275ef6 100644
--- a/helpers.c
+++ b/helpers.c
@@ -1,13 +1,53 @@
 #include "helpers.h"
 
-
+int min(int a,int b){
+    if(a<b) return a;
+    return b;
+}
+int max(int a,int b){
+    if(a>b) return a;
+    return b;
+}
 void grayscale(int height, int width, RGBTRIPLE image[height][width]){
-
+    return;
+    
 // Convert image to grayscale
 
 }
 
+void invert(int height, int width, RGBTRIPLE image[height][width]){
+    for(int i = 0; i<height; i++){
+        for(int j = 0; j<width; j++){
+            //Original RGB
+            int red = image[i][j].rgbtRed;
+            int green = image[i][j].rgbtGreen;
+            int blue = image[i][j].rgbtBlue;
+
+            //Normal inversion
+            int invRed = 255 - red;
+            int invGreen = 255 - green;
+            int invBlue = 255 - blue;
+
+            //for maintain average brightness
+            int originalBrightness = 0.299*red + 0.587*green + 0.114*blue;
+            int invertedBrightness = 0.299*invRed + 0.587*invGreen + 0.114*invBlue;
+            int brightnessDiff = originalBrightness - invertedBrightness;
+
+            invRed = min(max(invRed + brightnessDiff, 0), 255);
+            invGreen = min(max(invGreen + brightnessDiff, 0), 255);
+            invBlue = min(max(invBlue + brightnessDiff, 0), 255);
+
+            //Assign
+            image[i][j].rgbtRed = invRed;
+            image[i][j].rgbtGreen = invGreen;
+            image[i][j].rgbtBlue = invBlue;
+        }
+    }
+    return;
+    
+// Convert image to grayscale
 
+}
 void sepia(int height, int width, RGBTRIPLE image[height][width]){
 
 // Convert image to sepia
diff --git a/helpers.h b/helpers.h
index 412da8c..89790e5 100644
--- a/helpers.h
+++ b/helpers.h
@@ -3,6 +3,9 @@
 // Convert image to grayscale
 void grayscale(int height, int width, RGBTRIPLE image[height][width]);
 
+// invert image
+void invert(int height, int width, RGBTRIPLE image[height][width]);
+
 // Convert image to sepia
 void sepia(int height, int width, RGBTRIPLE image[height][width]);
 
diff --git a/output.bmp b/output.bmp
new file mode 100644
index 0000000..8abb92d
Binary files /dev/null and b/output.bmp differ