Fix ONNX dynamic axes export support with onnx simplifier, make onnx …

…simplifier optional (ultralytics#2856)

* Ensure dynamic export works succesfully, onnx simplifier optional

* Update export.py

* add dashes

Co-authored-by: Tim <tim.stokman@hal24k.com>
Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

models/export.py

@@ -21,12 +21,13 @@
 
 if __name__ == '__main__':
     parser = argparse.ArgumentParser()
-    parser.add_argument('--weights', type=str, default='./yolov5s.pt', help='weights path')  # from yolov5/models/
+    parser.add_argument('--weights', type=str, default='./yolov5s.pt', help='weights path')
     parser.add_argument('--img-size', nargs='+', type=int, default=[640, 640], help='image size')  # height, width
     parser.add_argument('--batch-size', type=int, default=1, help='batch size')
-    parser.add_argument('--dynamic', action='store_true', help='dynamic ONNX axes')
     parser.add_argument('--grid', action='store_true', help='export Detect() layer grid')
     parser.add_argument('--device', default='cpu', help='cuda device, i.e. 0 or 0,1,2,3 or cpu')
+    parser.add_argument('--dynamic', action='store_true', help='dynamic ONNX axes')  # ONNX-only
+    parser.add_argument('--simplify', action='store_true', help='simplify ONNX model')  # ONNX-only
     opt = parser.parse_args()
     opt.img_size *= 2 if len(opt.img_size) == 1 else 1  # expand
     print(opt)
@@ -58,7 +59,7 @@
     model.model[-1].export = not opt.grid  # set Detect() layer grid export
     y = model(img)  # dry run
 
-    # TorchScript export
+    # TorchScript export -----------------------------------------------------------------------------------------------
     prefix = colorstr('TorchScript:')
     try:
         print(f'\n{prefix} starting export with torch {torch.__version__}...')
@@ -69,7 +70,7 @@
     except Exception as e:
         print(f'{prefix} export failure: {e}')
 
-    # ONNX export
+    # ONNX export ------------------------------------------------------------------------------------------------------
     prefix = colorstr('ONNX:')
     try:
         import onnx
@@ -87,21 +88,24 @@
         # print(onnx.helper.printable_graph(model_onnx.graph))  # print
 
         # Simplify
-        try:
-            check_requirements(['onnx-simplifier'])
-            import onnxsim
-
-            print(f'{prefix} simplifying with onnx-simplifier {onnxsim.__version__}...')
-            model_onnx, check = onnxsim.simplify(model_onnx)
-            assert check, 'assert check failed'
-            onnx.save(model_onnx, f)
-        except Exception as e:
-            print(f'{prefix} simplifier failure: {e}')
+        if opt.simplify:
+            try:
+                check_requirements(['onnx-simplifier'])
+                import onnxsim
+
+                print(f'{prefix} simplifying with onnx-simplifier {onnxsim.__version__}...')
+                model_onnx, check = onnxsim.simplify(model_onnx,
+                                                     dynamic_input_shape=opt.dynamic,
+                                                     input_shapes={'images': list(img.shape)} if opt.dynamic else None)
+                assert check, 'assert check failed'
+                onnx.save(model_onnx, f)
+            except Exception as e:
+                print(f'{prefix} simplifier failure: {e}')
         print(f'{prefix} export success, saved as {f}')
     except Exception as e:
         print(f'{prefix} export failure: {e}')
 
-    # CoreML export
+    # CoreML export ----------------------------------------------------------------------------------------------------
     prefix = colorstr('CoreML:')
     try:
         import coremltools as ct