Abstract: The invention relates to methods for evaluation a brightness level of the digital x-ray image for medical applications by means of the image histogram using a neural network. The calculations comprise of: image acquisition, image histogram calculation, transformation the frequencies of the histogram into input arguments of the neural network and calculation the brightness level as linear transform of the output value of the neural network. Training of the neural network is performed over a learning set calculated over the given image database. The transformed frequencies of histograms of these images are used as a set of input arguments of the neural network. The brightness levels calculated for each image over the region of interest and scaled to the range of output values of the neuron network are used as a set of target values.