Update app.py

app.py

@@ -239,14 +239,22 @@ def merge_alpha(img, sigma=0.0):
     print(f"img.shape: {img.shape}")
     
     if C == 3:
+        img, _ = run_rmbg(img)
         return img
     elif C == 4:        
-        rgb = img[:, :, :3]
-        alpha = img[:, :, 3] 
-        result = 127 + (rgb.astype(np.float32) - 127 + sigma) * alpha[:, :, np.newaxis]        
+        rgb = img[:, :, :3].astype(np.float32)
+        alpha = img[:, :, 3].astype(np.float32) / 255.0  
+
+        result = rgb * alpha[:, :, np.newaxis] + 255 * (1 - alpha[:, :, np.newaxis])
+
+        if sigma != 0:
+            result += sigma * alpha[:, :, np.newaxis]
+
         return np.clip(result, 0, 255).astype(np.uint8)
     else:
         raise ValueError(f"Unexpected number of channels: {C}")
+    else:
+        raise ValueError(f"Unexpected number of channels: {C}")
 
 
 @torch.inference_mode()