Tonal conversion method for pictures

Claim 1

A tonal conversion method for producing a tonal converted reproduced picture from an original picture recorded on a given recording medium, the original being an image of a camera subject, which comprises the steps of: (i) determining a density characteristic curve which represents a correlation between density information values of the original picture plotted along the D axis of an X-D coordinate system and pictorial information values of the cameral subject plotted along the X axis of the X-D coordinate system; (ii) reproducing the original picture from the recording medium and determining an image density of picture elements of the original picture to obtain corresponding density information values D of the picture elements of the original picture; (iii) determining, from the density information values (D n ) of a desired picture element on the original picture, the pictorial information value X n of a corresponding picture element on the camera subject in accordance with said density characteristic curve; (iv) converting the thus-obtained pictorial information value X n of the camera subject into a tone intensity value (y) by using the following tonal conversion formula: ##EQU7## (v) generating and recording the tonal converted reproduced picture having picture elements in accordance with thus obtained corresponding tone intensity values; where x: a basic density value (X n -X Hn ) obtained by subtracting the pictorial information value (X Hn ) of the camera subject set by the density value (D Hn ) of the brightest area (H) on the original picture from the pictorial information value (X n ) of the camera subject set by the pictorial information value (D n ) relating to the density information of the desired picture element on the original in accordance with the density characteristic curve; y: a tone intensity value of the picture element on the reproduced picture corresponding to the desired picture element on the original picture; y H : a tone intensity values set for the brightest area (H) on the original picture or on the corresponding area of the camera subject; y s : a tone intensity value such as a dot area percentage set for the darkest area (S) on the original picture or on the corresponding area of the camera subject; α: a surface reflectance of a base material used for expressing the reproduced picture thereon; β: a value determined by β=10 - γ; k: γ/(X Sn -X Hn ), where X Sn represents the pictorial information value (X Sn ) of the camera subject determined by the density value (D Sn ) of the darkest area (S) on the original picture in accordance with density characteristic curve; and γ: a desired optional factor.