RuntimeError: Given groups=1, weight of size [64, 64, 1, 1], expected input[4, 1, 1080, 1920] to have 64 channels, but got 1 channels instead
I want to train a U-net segmentation model on the German Asphalt Pavement Distress (GAPs) dataset using U-Net. I'm trying to modify the model at https://github.com/khanhha/crack_segmentation to train on that dataset.
Here is the folder containing all the related files and folders:
https://drive.google.com/drive/folders/14NQdtMXokIixBJ5XizexVECn23Jh9aTM?usp=sharing
I modified the training file, and renamed it as &quot;train_unet_GAPs.py&quot;. When I try to train on Colab using the following command:
!python /content/drive/Othercomputers/My\ Laptop/crack_segmentation_khanhha/crack_segmentation-master/train_unet_GAPs.py -data_dir &quot;/content/drive/Othercomputers/My Laptop/crack_segmentation_khanhha/crack_segmentation-master/GAPs/&quot; -model_dir /content/drive/Othercomputers/My\ Laptop/crack_segmentation_khanhha/crack_segmentation-master/model/ -model_type resnet101

I get the following error:
total images = 2410
create resnet101 model
Downloading: &quot;https://download.pytorch.org/models/resnet101-63fe2227.pth&quot; to /root/.cache/torch/hub/checkpoints/resnet101-63fe2227.pth
100% 171M/171M [00:00&lt;00:00, 212MB/s]
Started training model from epoch 0
Epoch 0:   0% 0/2048 [00:00&lt;?, ?it/s]
Traceback (most recent call last):
  File &quot;/content/drive/Othercomputers/My Laptop/crack_segmentation_khanhha/crack_segmentation-master/train_unet_GAPs.py&quot;, line 259, in &lt;module&gt;
    train(train_loader, model, criterion, optimizer, validate, args)
  File &quot;/content/drive/Othercomputers/My Laptop/crack_segmentation_khanhha/crack_segmentation-master/train_unet_GAPs.py&quot;, line 118, in train
    masks_pred = model(input_var)
  File &quot;/usr/local/lib/python3.7/dist-packages/torch/nn/modules/module.py&quot;, line 1110, in _call_impl
    return forward_call(*input, **kwargs)
  File &quot;/content/drive/Othercomputers/My Laptop/crack_segmentation_khanhha/crack_segmentation-master/unet/unet_transfer.py&quot;, line 224, in forward
    conv2 = self.conv2(x)
  File &quot;/usr/local/lib/python3.7/dist-packages/torch/nn/modules/module.py&quot;, line 1110, in _call_impl
    return forward_call(*input, **kwargs)
  File &quot;/usr/local/lib/python3.7/dist-packages/torch/nn/modules/container.py&quot;, line 141, in forward
    input = module(input)
  File &quot;/usr/local/lib/python3.7/dist-packages/torch/nn/modules/module.py&quot;, line 1110, in _call_impl
    return forward_call(*input, **kwargs)
  File &quot;/usr/local/lib/python3.7/dist-packages/torchvision/models/resnet.py&quot;, line 144, in forward
    out = self.conv1(x)
  File &quot;/usr/local/lib/python3.7/dist-packages/torch/nn/modules/module.py&quot;, line 1110, in _call_impl
    return forward_call(*input, **kwargs)
  File &quot;/usr/local/lib/python3.7/dist-packages/torch/nn/modules/conv.py&quot;, line 447, in forward
    return self._conv_forward(input, self.weight, self.bias)
  File &quot;/usr/local/lib/python3.7/dist-packages/torch/nn/modules/conv.py&quot;, line 444, in _conv_forward
    self.padding, self.dilation, self.groups)
RuntimeError: Given groups=1, weight of size [64, 64, 1, 1], expected input[4, 1, 1080, 1920] to have 64 channels, but got 1 channels instead
Epoch 0:   0% 0/2048 [00:08&lt;?, ?it/s]

I think that this is because the images of GAPs dataset are grayscale images (with one channel), while Resnet expects to receive RGB images with 3 channels.
How can I solve this issue? How can I modify the model to receive grayscale images instead of RGB images? I need help with that. I have no experience with torch, and I think this implementation uses built-in Resnet model.

I figured out few things with your code.
According to the trace back, you are using a resnet based Unet model.
Your current model forward method is defined as :
def forward(self, x):
    #conv1 = self.conv1(x)
    #conv2 = self.conv2(conv1)
    conv2 = self.conv2(x)
    conv3 = self.conv3(conv2)
    conv4 = self.conv4(conv3)
    conv5 = self.conv5(conv4)
    ...

Your error comes from self.conv2(x), because, conv2 takes a matrix with a number of channels of 64. It means, something is missing, or.. commented :)
By changing
    #conv1 = self.conv1(x)
    #conv2 = self.conv2(conv1)
    conv2 = self.conv2(x)

into
    conv1 = self.conv1(x)
    conv2 = self.conv2(conv1) 

Will fix the problem the problem of 64 channels as input. But, there is another problem :
Using an input of (B,1,H,W), no matters what B, H and W are, won't be possible with your current architecture. Why ? Because of this :
resnet34 = torchvision.models.resnet34(pretrained=False)
resnet101 = torchvision.models.resnet101(pretrained=False)
resnet152 = torchvision.models.resnet152(pretrained=False)

print(resnet34.conv1)
-&gt; Conv2d(3, 64, kernel_size=(7, 7), stride=(2, 2), padding=(3, 3), bias=False)

print(resnet101.conv1)
-&gt; Conv2d(3, 64, kernel_size=(7, 7), stride=(2, 2), padding=(3, 3), bias=False)

print(resnet152.conv1)
-&gt; Conv2d(3, 64, kernel_size=(7, 7), stride=(2, 2), padding=(3, 3), bias=False)

In any case, the layer conv1 of resnet, takes a 3 channels input.
Once you have made those modifications, you should also try your network with a dummy example like :
model = UNetResNet(34,num_classes=2)
out = model(torch.rand(4,3,1920,1920))
print(out.shape)
-&gt; (4,2,1920,1920) | (batch_size, num_classes, H, W)

Why your width and height are the same here ? Because your current architecture only supports squared images.
For example :
-&gt; (1080,1920) = dim mismatching during concatenation part
-&gt; (1920,1920) = success
-&gt; (108,192) = dim mismatching during concatenation part
-&gt; (192,192) = success

Conclusion :

Modify your network to accept grayscale images if your dataset is made of grayscale images.
Preprocess your images to make Width=Height.

Edit (device mismatch) :
class UNetResNet(nn.Module):

    def __init__(self, encoder_depth, num_classes, num_filters=32, dropout_2d=0.2,
                 pretrained=False, is_deconv=False):
        super().__init__()
        self.num_classes = num_classes
        self.dropout_2d = dropout_2d

        if encoder_depth == 34:
            self.encoder = torchvision.models.resnet34(pretrained=pretrained)
            bottom_channel_nr = 512
        elif encoder_depth == 101:
            self.encoder = torchvision.models.resnet101(pretrained=pretrained)
            bottom_channel_nr = 2048
        elif encoder_depth == 152:
            self.encoder = torchvision.models.resnet152(pretrained=pretrained)
            bottom_channel_nr = 2048
        else:
            raise NotImplementedError('only 34, 101, 152 version of Resnet are implemented')

        self.pool = nn.MaxPool2d(2, 2)

        self.relu = nn.ReLU(inplace=True)

        #self.conv1 = nn.Sequential(self.encoder.conv1,
        #                           self.encoder.bn1,
        #                           self.encoder.relu,
        #                           self.pool)

        self.conv1 = nn.Sequential(nn.Conv2d(1,64,kernel_size=(7,7),stride=(2,2),padding=(3,3),bias=False), # 1 Here is for grayscale images, replace by 3 if you need RGB/BGR
                                   nn.BatchNorm2d(64),
                                   nn.ReLU(),
                                   self.pool
                                )
        
        self.conv2 = self.encoder.layer1

        self.conv3 = self.encoder.layer2

        self.conv4 = self.encoder.layer3

        self.conv5 = self.encoder.layer4

        self.center = DecoderBlockV2(bottom_channel_nr, num_filters * 8 * 2, num_filters * 8, is_deconv)
        self.dec5 = DecoderBlockV2(bottom_channel_nr + num_filters * 8, num_filters * 8 * 2, num_filters * 8, is_deconv)
        self.dec4 = DecoderBlockV2(bottom_channel_nr // 2 + num_filters * 8, num_filters * 8 * 2, num_filters * 8,
                                   is_deconv)
        self.dec3 = DecoderBlockV2(bottom_channel_nr // 4 + num_filters * 8, num_filters * 4 * 2, num_filters * 2,
                                   is_deconv)
        self.dec2 = DecoderBlockV2(bottom_channel_nr // 8 + num_filters * 2, num_filters * 2 * 2, num_filters * 2 * 2,
                                   is_deconv)
        self.dec1 = DecoderBlockV2(num_filters * 2 * 2, num_filters * 2 * 2, num_filters, is_deconv)
        self.dec0 = ConvRelu(num_filters, num_filters)
        self.final = nn.Conv2d(num_filters, num_classes, kernel_size=1)

    def forward(self, x):
        conv1 = self.conv1(x)
        conv2 = self.conv2(conv1)
        conv3 = self.conv3(conv2)
        conv4 = self.conv4(conv3)
        conv5 = self.conv5(conv4)

        pool = self.pool(conv5)
        center = self.center(pool)

        dec5 = self.dec5(torch.cat([center, conv5], 1))

        dec4 = self.dec4(torch.cat([dec5, conv4], 1))
        dec3 = self.dec3(torch.cat([dec4, conv3], 1))
        dec2 = self.dec2(torch.cat([dec3, conv2], 1))
        dec1 = self.dec1(dec2)
        dec0 = self.dec0(dec1)

        return self.final(F.dropout2d(dec0, p=self.dropout_2d))


