Convert PyTorch* YOLACT to the Intermediate Representation

You Only Look At CoefficienTs (YOLACT) is a simple, fully convolutional model for real-time instance segmentation. The PyTorch* implementation is publicly available in this GitHub* repository. The YOLACT++ model is not supported, because it uses deformable convolutional layers that cannot be represented in ONNX* format.

Create a Patch File

Before converting the model, create a patch file for the repository. The patch modifies the framework code by adding a special command-line argument to the framework options that enables inference graph dumping:

  1. Go to a writable directory and create a YOLACT_onnx_export.patch file.
  2. Copy the following diff code to the file:
From 76deb67d4f09f29feda1a633358caa18335d9e9f Mon Sep 17 00:00:00 2001
From: "OpenVINO" <openvino@intel.com>
Date: Fri, 12 Mar 2021 00:27:35 +0300
Subject: [PATCH] Add export to ONNX

---
 eval.py                |  5 ++++-
 utils/augmentations.py |  7 +++++--
 yolact.py              | 29 +++++++++++++++++++----------
 3 files changed, 28 insertions(+), 13 deletions(-)

diff --git a/eval.py b/eval.py
index 547bc0a..bde0680 100644
--- a/eval.py
+++ b/eval.py
@@ -593,9 +593,12 @@ def badhash(x):
     return x

 def evalimage(net:Yolact, path:str, save_path:str=None):
-    frame = torch.from_numpy(cv2.imread(path)).cuda().float()
+    frame = torch.from_numpy(cv2.imread(path)).float()
+    if torch.cuda.is_available():
+        frame = frame.cuda()
     batch = FastBaseTransform()(frame.unsqueeze(0))
     preds = net(batch)
+    torch.onnx.export(net, batch, "yolact.onnx", opset_version=11)

     img_numpy = prep_display(preds, frame, None, None, undo_transform=False)

diff --git a/utils/augmentations.py b/utils/augmentations.py
index cc7a73a..2420603 100644
--- a/utils/augmentations.py
+++ b/utils/augmentations.py
@@ -623,8 +623,11 @@ class FastBaseTransform(torch.nn.Module):
     def __init__(self):
         super().__init__()

-        self.mean = torch.Tensor(MEANS).float().cuda()[None, :, None, None]
-        self.std  = torch.Tensor( STD ).float().cuda()[None, :, None, None]
+        self.mean = torch.Tensor(MEANS).float()[None, :, None, None]
+        self.std  = torch.Tensor( STD ).float()[None, :, None, None]
+        if torch.cuda.is_available():
+            self.mean.cuda()
+            self.std.cuda()
         self.transform = cfg.backbone.transform

     def forward(self, img):
diff --git a/yolact.py b/yolact.py
index d83703b..f8c787c 100644
--- a/yolact.py
+++ b/yolact.py
@@ -17,19 +17,22 @@ import torch.backends.cudnn as cudnn
 from utils import timer
 from utils.functions import MovingAverage, make_net

-# This is required for Pytorch 1.0.1 on Windows to initialize Cuda on some driver versions.
-# See the bug report here: https://github.com/pytorch/pytorch/issues/17108
-torch.cuda.current_device()
-
-# As of March 10, 2019, Pytorch DataParallel still doesn't support JIT Script Modules
-use_jit = torch.cuda.device_count() <= 1
-if not use_jit:
-    print('Multiple GPUs detected! Turning off JIT.')
+use_jit = False

 ScriptModuleWrapper = torch.jit.ScriptModule if use_jit else nn.Module
 script_method_wrapper = torch.jit.script_method if use_jit else lambda fn, _rcn=None: fn


+def decode(loc, priors):
+    variances = [0.1, 0.2]
+    boxes = torch.cat((priors[:, :2] + loc[:, :, :2] * variances[0] * priors[:, 2:], priors[:, 2:] * torch.exp(loc[:, :, 2:] * variances[1])), 2)
+
+    boxes_result1 = boxes[:, :, :2] - boxes[:, :, 2:] / 2
+    boxes_result2 = boxes[:, :, 2:] + boxes[:, :, :2]
+    boxes_result = torch.cat((boxes_result1, boxes_result2), 2)
+
+    return boxes_result
+

 class Concat(nn.Module):
     def __init__(self, nets, extra_params):
@@ -476,7 +479,10 @@ class Yolact(nn.Module):

     def load_weights(self, path):
         """ Loads weights from a compressed save file. """
-        state_dict = torch.load(path)
+        if torch.cuda.is_available():
+            state_dict = torch.load(path)
+        else:
+            state_dict = torch.load(path, map_location=torch.device('cpu'))

         # For backward compatability, remove these (the new variable is called layers)
         for key in list(state_dict.keys()):
@@ -673,8 +679,11 @@ class Yolact(nn.Module):
                 else:
                     pred_outs['conf'] = F.softmax(pred_outs['conf'], -1)

-            return self.detect(pred_outs, self)
+            pred_outs['boxes'] = decode(pred_outs['loc'], pred_outs['priors']) # decode output boxes

+            pred_outs.pop('priors') # remove unused in postprocessing layers
+            pred_outs.pop('loc') # remove unused in postprocessing layers
+            return pred_outs



--
  1. Save and close the file.

Convert YOLACT Model to the Intermediate Representation (IR) format

Step 1. Clone the GitHub repository and check out the commit:

  1. Clone the YOLACT repository:
git clone https://github.com/dbolya/yolact
  1. Check out the necessary commit:
git checkout 57b8f2d95e62e2e649b382f516ab41f949b57239

Step 2. Download a pretrained model, for example yolact_base_54_800000.pth.

Step 3. Export the model to ONNX* format.

  1. Apply the YOLACT_onnx_export.patch patch to the repository. Refer to the Create a Patch File instructions if you do not have it:
git apply /path/to/patch/YOLACT_onnx_export.patch
  1. Evaluate the YOLACT model to export it to ONNX* format:
python3 eval.py \
    --trained_model=/path/to/yolact_base_54_800000.pth \
    --score_threshold=0.3 \
    --top_k=10 \
    --image=/path/to/image.jpg
  1. You should get yolact.onnx file.

Step 4. Convert the model to the IR:

python path/to/model_optimizer/mo.py --input_model /path/to/yolact.onnx

Step 4. Embed input preprocessing into the IR:

To get performance gain by offloading to the OpenVINO application of mean/scale values and RGB->BGR conversion, use the following options of the Model Optimizer (MO):

  • If the backbone of the model is Resnet50-FPN or Resnet101-FPN, use the following MO command line:
python path/to/model_optimizer/mo.py \
    --input_model /path/to/yolact.onnx \
    --reverse_input_channels \
    --mean_values "[123.68, 116.78, 103.94]" \
    --scale_values "[58.40, 57.12, 57.38]"
  • If the backbone of the model is Darknet53-FPN, use the following MO command line:
python path/to/model_optimizer/mo.py \
    --input_model /path/to/yolact.onnx \
    --reverse_input_channels \
    --scale 255