Say there is a convolutional layer that has 8 filters of size 3x3 and takes as input 28x28x1 images.
Then the output size will be 26x26x8.
So how are there 8 26x26 feature maps for that layer or just 1 26x26 feature map? If the answer is 1 feature map then how is it created since the output has 8 channels?