Thermal printing method

1. Method of generating a sharpened image on a printing material in a thermal printer which comprises an internal thermal model module that converts input values into power values for each element of a thermal head and for each printing cycle, comprising the steps of:

defining a function F(Mtw, b, c, d . . . ) wherein Mtw is a matrix of wanted temperature values for each of the heating elements of a thermal head and for all printing cycles, wherein at least a subset of parameters b, c, d . . . influences the behaviour of the function along the direction of said thermal head and a subset of said parameters b, c, d influences the behaviour of the function in a direction in which said printing material is transported past said thermal head,

defining a matching function Fm=aMtw+F(Mtw, b, c, d, . . . ) with a=1−c;

determining optimal values aopt, bopt, copt, dopt, . . . for said parameters a, b, c, d, . . . so that Fm(aopt, bopt, copt, dopt . . . ) simulates the behaviour of said printer

applying values Mtwc to said internal thermal model, said values Mtwc being equal to 1/aopt*(Mtw-F(Mtw, bopt, copt, dopt, . . . )).

2. A method according to claim 1 wherein optimal values aopt, bopt, copt, dopt for said parameters a, b, c, d are determined by

applying a test pattern to said thermal model module to generate a density pattern,

measuring densities of said generated density pattern,

calculating a reference matrix Mtm of values proportional to wanted heating element temperatures using the sensitometry of said printing material,

calculating a matrix Mtp by applying said test pattern to said matching function,

running an optimizing process to obtain optimal match between Mtp and Mtm thereby modifying said parameters a, b, c, d, . . . to generate values aopt, bopt, copt, dopt, . . . and

setting the parameters of said function F() equal to said values aopt, bopt, copt, dopt . . . .

3. A method according to claim 2 wherein said test pattern is a step wise pattern.

4. A method according to claim 1 wherein parameters ‘a’ equals ‘1−c’ and c represents the steady state value of said function F.

5. A method according to claim 1 wherein Mtw is a one dimensional array comprising values Ktw representing wanted temperature values for an individual cycle of the process of printing said sharpened image.

6. A method according to claim 1 wherein Mtw is a one dimensional array comprising values Ttw representing wanted temperature values for an element of the print head of said thermal printer.

7. A method according to claim 1 wherein

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