Method of assessing the activity of a photographic developer

Claim 1

A method of assessing the developing activity of a photographic developer relative to a norm, which method comprises the steps of using the developer to develop a latent photographic image of a sensitometric wedge, determining density curve data pertaining to the resulting wedge print (hereinafter and in subsequent claims called "control print") by means of a photoelectric transmission densitometer, and comparing such data with analogous data pertaining to at least one reference wedge print resulting from the development of an identical latent sensitometric wedge image in a developer of given activity taken as norm, characterised in that the densitometer is used to determine in respect of the control print: (i) a notional density range in terms of the difference between the dark current of the photodetector of the densitometer and the output current of such detector when it is irradiated by light through the transparent support of such control print at an area of zero image density, and (ii) to determine at least one position along the control print where its image density, as measured in terms of the output current of said detector, is in a predetermined ratio to said notional density range; the data thus established pertaining to the control print is compared with analogous data pertaining to the reference print, established by means of the same densitometer, in order to determine the relationship between the positions along the control and reference prints at which their notional densities are in the same ratio to their respective notional density ranges, and the said relationship is used as a measure of the developing activity of the developer being assessed.