Update app.py

app.py

@@ -78,6 +78,13 @@ def add_heading(img, text):
     cv2.putText(canvas, text, (10, 30), cv2.FONT_HERSHEY_SIMPLEX, 1, (0,0,0), 2, cv2.LINE_AA)
     return canvas
 
+# ---------------- Placeholder if matching fails ----------------
+def get_placeholder(method):
+    canvas = np.ones((600, 1800, 3), dtype=np.uint8) * 255
+    cv2.putText(canvas, f"{method}: Not enough feature matching", (50, 300),
+                cv2.FONT_HERSHEY_SIMPLEX, 2, (0,0,255), 3, cv2.LINE_AA)
+    return canvas
+
 # ---------------- Main Function ----------------
 def homography_all_detectors(flat_file, persp_file, json_file, xml_file):
     flat_img = cv2.imread(flat_file)
@@ -101,12 +108,22 @@ def homography_all_detectors(flat_file, persp_file, json_file, xml_file):
     for method in methods:
         kp1,kp2,good_matches = detect_and_match(flat_gray,persp_gray,method)
         if kp1 is None or kp2 is None or len(good_matches)<4:
+            placeholder = get_placeholder(method)
+            fname = f"{method.lower()}_placeholder.png"
+            cv2.imwrite(fname, placeholder)
+            gallery_paths.append(fname)
+            download_files.append(fname)
             continue
 
         src_pts = np.float32([kp1[m.queryIdx].pt for m in good_matches]).reshape(-1,1,2)
         dst_pts = np.float32([kp2[m.trainIdx].pt for m in good_matches]).reshape(-1,1,2)
         H,_ = cv2.findHomography(src_pts,dst_pts,cv2.RANSAC,5.0)
         if H is None:
+            placeholder = get_placeholder(method)
+            fname = f"{method.lower()}_placeholder.png"
+            cv2.imwrite(fname, placeholder)
+            gallery_paths.append(fname)
+            download_files.append(fname)
             continue
 
         # 1. Flat image with ROI (from JSON)
@@ -119,7 +136,7 @@ def homography_all_detectors(flat_file, persp_file, json_file, xml_file):
         # 2. Perspective with Homography ROI
         roi_corners_persp = cv2.perspectiveTransform(roi_corners_flat.reshape(-1,1,2),H).reshape(-1,2)
         persp_roi = persp_img.copy()
-        cv2.polylines(persp_roi,[roi_corners_persp.astype(int)],True,(0,255,0),5) #--------------------thicknes------------------------------------
+        cv2.polylines(persp_roi,[roi_corners_persp.astype(int)],True,(0,255,0),5)
         for px,py in roi_corners_persp:
             cv2.circle(persp_roi,(int(px),int(py)),5,(255,0,0),5)