[FIXED] How to change Tensor format to channels first in Tensorflow js?

Issue

I'm new to Computer Vision model structure, and I'm using Tensorflow for Node JS @tensorflow/tfjs-node to make some models detect some objects. With Mobilenet and Resnet SSD, the models are using the Channels Last format, so when I create a Tensor with tf.node.decodeImage the format is by default Channels Last, like shape: [1, 1200, 1200, 3] for 3 channels, and the predictions data work great, able to recognize objects.

But model from Pytorch, converted to ONNX, then to Protobuf PB format, the saved_model.pb has the Channels First format, like shape: [1, 3, 1200, 1200].

Now I need to create Tensor from image but with Channels First format. I found many exemple of creating conv1d, conv2d specifying the format dataFormat='channelsFirst'. But I don't know how to apply it to an image data. Here is the API https://js.tensorflow.org/api/latest/#layers.conv2d .

Here is the Tensor codes:

const tf = require('@tensorflow/tfjs-node');
let imgTensor = tf.node.decodeImage(new Uint8Array(subBuffer), 3);
imgTensor = imgTensor.cast('float32').div(255);
imgTensor = imgTensor.expandDims(0); // to add the most left axis of size 1
console.log('tensor', imgTensor);

This gives me a shape with channels last that is not compatible with the Model shape with channels first:

tensor Tensor {
  kept: false,
  isDisposedInternal: false,
  shape: [ 1, 1200, 1200, 3 ],
  dtype: 'float32',
  size: 4320000,
  strides: [ 4320000, 3600, 3 ],
  dataId: {},
  id: 7,
  rankType: '4',
  scopeId: 4
}

I know of tf.shape, but it reshapes without converting to channels first, and the result seems useless in predictions results. Don't know what I'm missing.

Solution

you can use something like this:

const nchw = tf.transpose(nhwc, [0, 3, 1, 2]);

Answered By - Vladimir Mandic