# ResNet output dimensions

So I am currently going over the ResNet paper and trying to understand the output dimensions of each of the layer, and it seems that I am already stuck on the first layer and its output dimension.

If I understand correctly, the size of output of a particular layer can be calculated as (ORIGINAL_SIZE - FILTER_SIZE) / STRIDE + 1

In the plain example of the ResNet, presented below on the right hand side, they claim they use 224x224 image. Therefore, when I calculate the output dimension of the 7x7 convolution with stride 2, I get

(224 - 7) / 2 + 1 = 109.5, so I round it 110.

However, in the paper they claim that their output size is 112. How would that be possible? • 112=224/2 seems to be the correct calculation. – Yuval Filmus Mar 9 '18 at 13:37
• @YuvalFilmus so where is the 7x7 convolution? – Johhny Bravo Mar 9 '18 at 14:50
• It's probably an implementation detail. Maybe they apply the convolution even outside the boundary of the actual image. It's not a big deal. – Yuval Filmus Mar 9 '18 at 14:52
• I am asking as I am trying to understand what happens when remaining size is 1, but there is still a convolution layer with filter size greater than the actual width. – Johhny Bravo Mar 9 '18 at 15:13