How to load Image Masks (Labels) for Image Segmentation in Keras

Since this is semantic segmentation, you are classifying each pixel in the image, so you would be using a cross-entropy loss most likely. Keras, as well as TensorFlow require that your mask is one hot encoded, and also, the output dimension of your mask should be something like [batch, height, width, num_classes] <- which you will have to reshape the same way as your mask before computing your cross-entropy mask, which essentially means that you would have to reshape your logits and mask to the tensor shape [-1, num_classes] where -1 denotes 'as many as required'.

Have a look here at the end

Since your question is about loading your own image, I just finished building an input pipeline for segmentation myself, it is in TensorFlow though, so I don't know if it helps you, have a look if you are interested: Tensorflow input pipeline for segmentation