How to use grayscale image?

[sangyo1]

Hello,
I am using "mobilenetv2 ssd fpnlite 320x320" to train my own object detection model. However, I am trying to use grayscale images for both training and deploying the tflite model. I know that even when I input 1-channel images, the output becomes 3-channel by duplicating one channel into three. I find this unnecessary and want to avoid wasting memory and CPU usage, especially since I plan to deploy my model in grayscale. Which file must I change to create a 1-channel model instead of a 3-channel model?

Is it "https://github.com/tensorflow/models/blob/master/research/object_detection/export_tflite_graph_lib_tf2.py" file?