pythoneinops

EinopsError: Error while processing rearrange-reduction pattern "(b1 b2) h w c -> (b1 h) (b2 w) c"

I'm learning the basics of einops to incorporate in my code.

process = transforms.Compose([
    transforms.Resize(225),
    transforms.ToTensor()
])

cat = Image.open('cat.jpeg').convert('RGB')

cat = process(cat)

rearrange(cat, '(b1 b2) h w c -> (b1 h) (b2 w) c', b1=2, b2=2)

Raises the error:

EinopsError:  Error while processing rearrange-reduction pattern "(b1 b2) h w c -> (b1 h) (b2 w) c".
 Input tensor shape: torch.Size([3, 337, 225]). Additional info: {'b1': 2, 'b2': 2}.
 Expected 4 dimensions, got 3

The error message seems pretty obvious, since I'm specifying 4 patches the output should be of the dimensions (patches, c, h , w). However, I'm not sure where am I supposed to specify that. I went over the tutorials by einops but I still didn't really find what is wrong here.

Solution

  • Einops message is exactly right in this case: in your pattern input has 4 dimensions: '(b1 b2) h w c', but you provide a tensor with only three dimensions.

    You should process a batch of 4 images and stack them to get a 4 dim tensor. Your current transformation gets 3-dim tensor (single image) and returns 3-dim tensor.