I think the first suggestion won’t work, as your alpha channel contains valid information, so you would have to apply one of the following:



 ptrblck:

To fix this issue you could

remove the alpha channel from your images in case it’s all 255 anyway
load the original model with 3 input channels and replace the first conv layer (newly initialized with 4 channels)
do as described before, but fill the first 3 channels with the pretrained weights and leave the last channel randomly initialized (not sure if that’ll work out)