Add two operators to support TFLite SSD Mobilenet models


I downloaded TF SSD quantized model ssd_mobilenet_v1_quantized_coco from
Tensorflow Model Zoo

The zip file contains tflite_graph.pb
I used tflite_convert util to convert tflite_graph.pb to model.tflite file

tflite_convert \
--graph_def_file=/home/ubuntu/ssd_mobilenet_v1_quantized_300x300_coco14_sync_2018_07_18/tflite_graph.pb \
--output_file=/home/ubuntu/ssd_mobilenet_v1_quantized_300x300_coco14_sync_2018_07_18/model.tflite \
--output_format=TFLITE \
--input_arrays="normalized_input_image_tensor" \
--input_shapes="1,300,300,3" \
--inference_type=QUANTIZED_UINT8 \
--mean_values=128 \
--std_dev_values=128 \
--output_arrays="TFLite_Detection_PostProcess,TFLite_Detection_PostProcess:1,TFLite_Detection_PostProcess:2,TFLite_Detection_PostProcess:3" \

SSD Mobilenet model.tflite Summary:

### Ops:
# id:   name    -   count
 3: CONV_2D  - 34
14: LOGISTIC - 1
22: RESHAPE - 13
32: CUSTOM - 1

When I tried to compile model.tflite using TVM relay I got the following error

Traceback (most recent call last):
  File "./", line 62, in <module>
    dtype_dict={input_tensor: input_dtype})
  File "/usr/local/lib/python3.5/dist-packages/tvm-0.6.dev0-py3.5-linux-x86_64.egg/tvm/relay/frontend/", line 709, in from_tflite
  File "/usr/local/lib/python3.5/dist-packages/tvm-0.6.dev0-py3.5-linux-x86_64.egg/tvm/relay/frontend/", line 84, in check_unsupported_ops
    raise tvm.error.OpNotImplemented(msg.format(ops))

tvm.error.OpNotImplemented: The following operators are not supported in frontend TFLite: 'LOGISTIC', 'CUSTOM'

Relay does not support 2 operators - 1 built-in and 1 custom
built-in - LOGISTIC (op_code_id = 14)
custom - TFLite_Detection_PostProcess (op_code_id = 32)

Looks like tf.sigmoid op in tflite_graph.pb is mapped to tflite LOGISTIC op.
LOGISTIC is generalized sigmoid.

TFLite_Detection_PostProcess is custom op which produces final 4 outputs - (classes, scores, bboxes and num_outputs)


My first questions are:

  1. Do you think it makes sense to add TFLite built-it LOGISTIC operator to relay? It should be similar to tf.sigmoid

  2. The Same question for custom operator TFLite_Detection_PostProcess.
    This operator is the last operator in TFLite graph in all SSD models from TF model zoo.

BTW, custom operator TFLite_Detection_PostProcess is optional. which converts checkpoint to TFLite compatible pb file has parameter add_postprocessing_op=true/false.
It is possible to create tflite_graph.pb without TFLite_Detection_PostProcess
in that case the model output will be

the graph has two outputs:
   raw_outputs/box_encodings: a float32 tensor of shape [1, num_anchors, 4]
    containing the encoded box predictions.
   raw_outputs/class_predictions: a float32 tensor of shape
    [1, num_anchors, num_classes] containing the class scores for each anchor
    after applying score conversion.


I also tried to compile SSD Resnet 50 model (ssd_resnet_50_fpn_coco)
It complains about the same two operators plus two additional operators: MUL and PAD
SSD Resnet 50 tflite summary:

 0: ADD - 58
 3: CONV_2D - 110
14: LOGISTIC - 1
17: MAX_POOL_2D - 4
18: MUL - 42
22: RESHAPE - 14
32: CUSTOM - 1
34: PAD - 1

Visualisation of TFLite graphs are below:

TFLite model graph for ssd_mobilenet_v1_quantized_coco (quantized, Uint8):

I also tried to compile non-quantized tflite model. The same 2 operators are missing.
TFLite model graph for ssd_mobilenet_v1_coco_2018_01_28 (non-quantized, float):

SSD Resnet 50 FPN COCO model graph


@FrozenGene @tqchen What you think?



For Custom Op, maybe I prefer letting users add_postprocessing_op= false.



@apivovarov Hi, if add_postprocessing_op=false, how can we get bbox x,y,h,w? I follow your step,
but get some strange box data,like [ -1.1977348 0.29819602 -1.3088214 -0.08522664]


We need to implement TFLite_Detection_PostProcess in python numpy and run it after getting model output.
Original implementation is here:

anchors tensors values (Constants) [1917,4] float32 can be extracted from tflite_graph.pb or tflite_graph.pbtxt files

node {
  name: "anchors"
  op: "Const"
  attr {
    key: "dtype"
    value {
      type: DT_FLOAT
  attr {
    key: "value"
    value {
      tensor {
        dtype: DT_FLOAT
        tensor_shape {
          dim {
            size: 1917
          dim {
            size: 4
        tensor_content: "6\224\327<6\224\327<\315\31..

I already extracted anchors for ssd_mobilenet_v1_coco_2018_01_28 and saved values to anchors.npy


Get it. Thanks for your anchor data.