Question
Hello, im using Unet to perform semantic segmentation (I want to segment liver metastasis). I want to weight 'more' the pixels of the metastasis respect to the background but I can't manage to do it... Code for creating unet architecture: lgraph = unetLayers(imageSize, numClasses, 'EncoderDepth', 4); How can I change the 'classWeights' in lgraph.Layers(end).pixelClassificationLayer in order to do this?? If, for example, I do this: lgraph.Layers(end).pixelClassificationLayer.classWeights = [2, 0.5]; I receive an error telling me that i have first to put the 'labels' to the 'classes' options in lgraph.Layers(end), but if i do this: lgraph.Layers(end) = {'metastasis', 'background'}; I receive an error telling that that layer is in 'read only' mode....
Expert Answer
John Michell
PhD Expert
Answered Aug 16, 2026
Hi,
The unetLayers object in MATLAB is in read only mode and we cannot change the properties of layers as such. You may remove the last layer which is the Segmentation-Layer and can add a new Segmentation-Layer with the properties that are mentioned.
Following Code will help.
% Last Layer Name is 'Segmentation-Layer'
% for checking layer name use :- lgraph.Layers
lgraph = removeLayers(lgraph,'Segmentation-Layer');
layerlast = pixelClassificationLayer('Classes',{'metastatis','background'},'ClassWeights',[2,0.5],'Name','New_segmentation_Layer');
layer_to_add = [layerlast];
lgraph = addLayers(lgraph,layer_to_add);
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