1. Apparatus for the treatment of numerical information representative of successive elements of an image to be displayed on a screen of a cathode unit of a visual display system, the information being recorded in a memory of the visual display system and defining data characteristic of the aspect of the successive elements of the image applied to the cathode unit in relation to the scale of said elements, said apparatus comprising a first circuit including a comparator connected to the memory to receive said data, a first register connected to said first circuit for supplying the same with at least one reference data defining different zones on a scale defining variations of the values of the data, said first circuit delivering an output signal characteristic of one of the zones according to the value of each bit of data with respect to the reference value, a multiplier circuit connected to and controlled by the output signal of the said comparator, a first control switch connected to said multiplier circuit, second registers memorizing different predetermined multiplication coefficients connected to said first control switch such that the multiplier circuit is capable, respectively, of expanding different zones of the data over the entire scale of values, a second control switch connected to said multiplier circuit, said second control switch having one input connected directly to the memory, a subtractor connected to said memory and said first circuit and capable of forming the difference between the value of each bit of the data and the value of each reference, said second control switch having a second input connected to said subtractor and a third register coupled to said comparator and memorizing at least one constant data value defined in the scale of values of the data and controlled by the output signal of the comparator, the output of the said third register and the output of the multiplier circuit forming the output of the treatment apparatus and comprising, additionally, a control circuit for one mode of treatment of the data selected from a number of treatment modes defined from the selection of each reference data of each constant value data and from a zone of the said scale, said control circuit being coupled to said first and third registers and to said switches to modify the values of the data delivered at the output of the treatment apparatus, and thus applied to the said cathode unit according to the selected mode of treatment.