Can a fully convolutional network always return an image of the same size as the original?

Question

I'm trying to perform a segmentation task on images of multiple sizes using fully convolutional neural networks.

Currently, I'm using EfficientNet as a feature extractor, and adding a deconvolution/backwards convolution/transposed convolution layer as described in the original Fully Convolutional Networks for Semantic Segmentation paper.

But this transposed convolution layer doesn't return a filter of a size equivalent to the original image for images of varying sizes.

For example, let's assume the original image is $100 \times 100$, and the last layer contains filters of size $50 \times 50$. To get a filter of the same size as the original, you would need a transposed convolution layer of size $51 \times 51$.

Now, assume you passed in an image of size $200 \times 200$. The last layer would contain filters of size $100 \times 100$. That same transposed convolutional filter of size $51 \times 51$ would result in an output of size $150 \times 150$.

Is there any way to make it so that a fully convolutional network always returns an image of the same size as the original?

Answer 1

I ended up using a work around.

I set up the network so that an C x C (i.e. 320 x 320) input would output a C x C mask for some constant C (in my case it was 320).

I then resized the image I wanted to pass in to C x C, and then resized the output back to the original size of the Image.