Criterion Target is out of bounds

I found a model that looked appealing to me at:

As a start I copied nearly everything from this website.
Firstly I want to explain my train and test datasets.

My Train Dataset contains some chinese signs as bitmaps with unknown “meaning” ( I am looking for unicode escapes)
My Test Dataset contains the range of simplified chinese characters as bitmaps (escape sequences are known).

I thought it would be better to do it this way as there are more than 22000 signs in simplified chinese. For training I would have needed more than one image per sign resulting in like 130000 pictures for training.
I only have 225 unknown bitmaps. By doing so I only have 225*6 pictures for training which I thought would be way better for performance.

Here is where I changed the code from the website:

def load_train_test():

    normalize = transforms.Normalize(mean=[0.5,],

    img_transforms = transforms.Compose([transforms.Resize(224),

    train_data = datasets.ImageFolder(TRAIN_DS,
                                      transform = img_transforms)

    test_data = datasets.ImageFolder(TEST_DS,
                                     transform = img_transforms)

    train_loader =, batch_size=64)
    test_loader =, batch_size=64)

    return train_loader, test_loader

In the example he created labels from SubsetRandomSampler().

Now I receive following error message:

Exception has occurred: IndexError
Target 10 is out of bounds.

The error occurs when I try to calculate loss at

loss = criterion(logps, labels)

Here is the code snippet (line 7)

for epoch in range(epochs):
    for inputs, labels in train_loader:
        steps += 1
        inputs, labels =,
        logps = model.forward(inputs)
        loss = criterion(logps, labels)
        running_loss += loss.item()

        if steps % print_every == 0:
            test_loss = 0
            accuracy = 0
            with torch.no_grad():
                for inputs, labels in test_loader:
                    inputs, labels =,
                    logps = model.forward(inputs)
                    batch_loss = criterion(logps, labels)
                    test_loss += batch_loss.item()

                    ps = torch.exp(logps)
                    top_p, top_class = ps.topk(1, dim=1)
                    equals = top_class == lavels.view(*top_class.shape)
                    accuracy = torch.mean(equals.type(torch.FloatTensor)).item()
            print(f"Epoch {epoch+1}/{epochs}.."
                  f"Train loss: {running_loss/print_every:.3f}.."
                  f"Test loss: {test_loss/len(test_loader):.3f}.."
                  f"Test accuracy: {accuracy/len(test_loader):.3f}")
            running_loss = 0
            model.train(), 'chinese.pth')

In debug mode I can see that there are some labels generated. I really don’t know why this error occurs.
Maybe someone of you knows what I am doing wrong.
Thanks for your time!

I assume you are using nn.CrossEntropyLoss as the criterion.
In that case, the model output should contain logits and have the shape [batch_size, nb_classes], while the target would have the shape [batch_size] and contain the class indices in the range [0, nb_classes-1].
The error is raised, if your target uses out-of-bounds class indices.
E.g. for 10 classes, the valid target values would be [0, 9], while you are trying to pass a 10 to the criterion.

Also, don’t call the forward method, as it will not call potentially registered hooks. Call the model directly instead: output = model(inputs).

As criterion I use nn.NLLLoss.
How can I fix the worng number of classes?
I should have 225 classes so I’m not sure why its already failing at 10 classes.

Thank you for that hint, I changed the forward line

I guess the output of your model is not containing logits for all 225 classes, which would be defined by the last layer (nn.Linear in case you are working on a multi-class classification).
Change the out_features to 225 and it should work.

This is my model description. Should I change

model.fc = nn.Sequential(nn.Linear(2048, 512),
                         nn.Linear(512, 10),


model.fc = nn.Sequential(nn.Linear(2048, 512),
                         nn.Linear(512, 225),

This creates the same error. Now Target 225 is out of bounds.
Could this happen because I do not specify targets while I’m loading the images?

Okay I guess the part of

if steps % print_every == 0:

is the problem.
As my test dataset contains 22222 “classses”(22222 signs) I would need 22222 as out_feature. Since this has nothing to do with my problem I will delete it and figure out some evaluation process and then share my solution here again.
As I simply copied this from the website I didn’t think of its purpose. I guess the best solution to this problem would be if I generate some more images of those 225 unknown images and test the accuracy of this neural net with them so the labels are fitting.

Your target index of 225 implies 226 classes (class indices would be in the range [0, 225], which are 226 values), so your model should also return 226 output logits.