A multimodal neural network implemented by a computer system comprising a predefined list of object types, for semantic segmentation of a complex text document to be processed, characterized in that it comprises: ∘ a first multilayer neural chain for encoding an initial digital image file of the document to be processed, with a determined initial dimension, the first encoding neural chain having an input receiving the initial digital image file of the document to be processed, a plurality of calculation layers (E(j)) generating files with determined dimensions, and an output, ∘ a second multilayer neural chain for encoding a mask image file of the document to be processed, with a determined initial dimension, generated at the end of a segmentation operation performed on a text file obtained by character recognition of the initial digital image file of the document to be processed, the segmentation operation further comprising the assignment to each word of the digital text file of an object type chosen from the predefined list of object types and the replacement of each word by a value field corresponding to the object type assigned to said word, the second encoding neural chain having an input receiving the mask image file, a plurality of calculation layers (E'(j)) generating files with determined dimensions, and an output; ∘ a decoding multilayer neural chain connected to the output of the first encoding multilayer neural chain and to the output of the second encoding multilayer neural chain, and comprising a plurality of calculation layers (D(j)) generating files with determined dimensions; ∘ a first bridge of parallel residual connections (CR40(k)) between the layers (E(j)) of the first encoding multilayer neural chain and the layers (D(j)) of the decoding multilayer neural chain, ∘ a second bridge of parallel residual connections (CR50(k)) between the layers (E'(j)) of the second encoding multilayer neural chain and the layers (D(j)) of the decoding multilayer neural chain, the parallel residual connections (CR40(k), CR50(k)) of the first and second bridges (40, 50) of residual connections generating files of the same size being connected after a layer (D(j)) of the decoding multilayer neural chain generating a semantic segmentation mask image file consisting of value-coded pixels, each value corresponding to an object type from the predefined list, the semantic segmentation mask image file being of the same dimension as the initial digital image file. ∘ a first multilayer neural chain for encoding an initial digital image file of the document to be processed, with a determined initial dimension, the first encoding neural chain having an input receiving the initial digital image file of the document to be processed, a plurality of calculation layers (E(j)) generating files with determined dimensions, and an output, ∘ a second multilayer neural chain for encoding a mask image file of the document to be processed, with a determined initial dimension, generated at the end of a segmentation operation performed on a text file obtained by character recognition of the initial digital image file of the document to be processed, the segmentation operation further comprising the assignment to each word of the digital text file of an object type chosen from the predefined list of object types and the replacement of each word by a value field corresponding to the object type assigned to said word, the second encoding neural chain having an input receiving the mask image file, a plurality of calculation layers (E'(j)) generating files with determined dimensions, and an output; ∘ a decoding multilayer neural chain connected to the output of the first encoding multilayer neural chain and to the output of the second encoding multilayer neural chain, and comprising a plurality of calculation layers (D(j)) generating files with determined dimensions; ∘ a first bridge of parallel residual connections (CR40(k)) between the layers (E(j)) of the first encoding multilayer neural chain and the layers (D(j)) of the decoding multilayer neural chain, ∘ a second bridge of parallel residual connections (CR50(k)) between the layers (E'(j)) of the second encoding multilayer neural chain and the layers (D(j)) of the decoding multilayer neural chain, the parallel residual connections (CR40(k), CR50(k)) of the first and second bridges (40, 50) of residual connections generating files of the same size being connected after a layer (D(j)) of the decoding multilayer neural chain generating a semantic segmentation mask image file consisting of value-coded pixels, each value corresponding to an object type from the predefined list, the semantic segmentation mask image file being of the same dimension as the initial digital image file.