Abstract: A process for preparing symmetrical or asymmetrical trans-thiazineindigo pigments of the formula (1) which comprises a) condensing, in an aqueous medium, a compound of the formula (2) with a compound of the formula (3a) or (3b) or a compound of the formula (4) with a compound of the formula (3a) and/or (3b)  by maintaining the reaction mixture at a temperature between 30 and 65° C. for at least 1 hour and then b) maintaining the reaction mixture at a temperature between 100 and 180° C. and a pressure between 2 and 50 bar for at least 1 hour in the presence of an amide.