Given groups=1, weight of size [10, 1, 5, 5], expected input[2, 3, 28, 28] to have 1 channels, but got 3 channels instead

Question

I am trying to run CNN with train MNIST, but test on my own written digits. To do that I wrote the following code but I getting an error in title of this questions: I am trying to run CNN with train MNIST, but test on my own written digits. To do that I wrote the following code but I getting an error in title of this questions:

batch_size = 64
train_dataset = datasets.MNIST(root='./data/',
                               train=True,
                               transform=transforms.ToTensor(),
                               download=True)
test_dataset = ImageFolder('my_digit_images/', transform=transforms.ToTensor())
train_loader = torch.utils.data.DataLoader(dataset=train_dataset,
                                           batch_size=batch_size,
                                           shuffle=True)
test_loader = torch.utils.data.DataLoader(dataset=test_dataset,
                                          batch_size=batch_size,
                                          shuffle=False)
class Net(nn.Module):

    def __init__(self):
        super(Net, self).__init__()
        self.conv1 = nn.Conv2d(1, 10, kernel_size=5)
        #print(self.conv1.weight.shape)
        self.conv2 = nn.Conv2d(10, 20, kernel_size=5)
        self.conv3 = nn.Conv2d(20, 20, kernel_size=3)
       #print(self.conv2.weight.shape)
        self.mp = nn.MaxPool2d(2)
        self.fc = nn.Linear(320, 10)

    def forward(self, x):
        in_size = x.size(0)
        x = F.relu(self.conv1(x))
        #print(x.shape)
        x = F.relu(self.mp(self.conv2(x)))
        x = F.relu(self.mp(self.conv3(x)))
        
        #print("2.", x.shape)
       # x = F.relu(self.mp(self.conv3(x)))
        x = x.view(in_size, -1)  # flatten the tensor
        #print("3.", x.shape)
        x = self.fc(x)
        return F.log_softmax(x)
model = Net()
optimizer = optim.SGD(model.parameters(), lr=0.01, momentum=0.5)
def train(epoch):
    model.train()
    for batch_idx, (data, target) in enumerate(train_loader):
        data, target = Variable(data), Variable(target)
        optimizer.zero_grad()
        output = model(data)
        loss = F.nll_loss(output, target)
        loss.backward()
        optimizer.step()
        if batch_idx % 10 == 0:
            print('Train Epoch: {} [{}/{} ({:.0f}%)]\tLoss: {:.6f}'.format(
                epoch, batch_idx * len(data), len(train_loader.dataset),
                100. * batch_idx / len(train_loader), loss.item()))


def test():
    model.eval()
    test_loss = 0
    correct = 0
    for data, target in test_loader:
        data, target = Variable(data, volatile=True), Variable(target)
        output = model(data)
        test_loss += F.nll_loss(output, target, size_average=False).data
        pred = output.data.max(1, keepdim=True)[1]
        correct += pred.eq(target.data.view_as(pred)).cpu().sum()

    test_loss /= len(test_loader.dataset)
    print('\nTest set: Average loss: {:.4f}, Accuracy: {}/{} ({:.0f}%)\n'.format(
        test_loss, correct, len(test_loader.dataset),
        100. * correct / len(test_loader.dataset)))

Answer 1

MNIST dataset contains black and white 1-channel images, while yours are 3-channeled RGB probably. Either recode your images or preprocess it like

img = img[:,0:1,:,:]

You can do it with custom transform, adding it after transforms.ToTensor()