Hi,
I am trying to change the first layer in resnet-50-fpn backbone inside Mask R-CNN provided in torchvision library. I changed it to 4 channels for RGB-depth input data while keeping the weights for first 3 channels using the following code:
self.backbone = resnet_fpn_backbone(arch, pretrained)
# change first layer to 4 channel for early fusion with 1 channel depth, load pretrained weights on RGB channels
conv1_weight_old = self.backbone.body.conv1.weight
conv1_weight = torch.zeros((64, 4, 7, 7))
conv1_weight[:, 0:3, :, :] = conv1_weight_old
avg_weight = conv1_weight_old.mean(dim=1, keepdim=False)
conv1_weight[:, 3, :, :] = avg_weight
self.backbone.body.conv1.weight = torch.nn.Parameter(conv1_weight)

The problem is very weird: it gives ‘CUDA out of memory error’ after training 1 or 2 epochs and starts a new one. I checked gpu memory is full when I stop the program in debug mode on the line it passes forward the backbone. I made a test to train 10 epochs using 10 images. It sometimes works fine and pass all epochs, but in most cases it gives memory error.
I also tried commenting two lines calculating average but it makes no difference.
The first conv layer in resnet was like this before changing its shape
nn.Conv2d(3, 64, kernel_size=7, stride=2, padding=3, bias=False)