Alastair M. Robinson wrote: > Hi, > Gerhard Fuernkranz wrote: > >> And I tend to agree - when the "gamma" value is getting too large >> then a wedge with a linearly spaced steps in device space is possibly >> no longer optimal for characterizing the response wrt. a perceptual >> metric. > > Yup - but to my mind the bigger problem is that such a gamma > adjustment means ink coverage is no longer directional proportional to > input value, This applies indeed to the other, gamma-adjusted space presented by the driver to the user. It certainly suffers from the problem that summing the colorant values won't sum up the actual ink amounts (but there is a non-linear relationship). I understand that this is the obvious reason why you wanted to calibrate the _raw_ space of the halftoning engine instead. There was likely a misunderstanding regarding my statement you cited above. I actually meant that I agree that for characterizing the _RAW_ space of the halftoning engine (i.e. the space with the extremely high dot gain (or extremely high "gamma")), a wedge with linear steps in device space is likely no longer optimal (but a non-linearly spaced wedge may be more suitable). But back to the TAC calculation: While for a printer with CMYK inks only the raw space of the halftoning engine may indeed have the desired properties (i.e. laid down ink amount proportional to the colorant value sent to the driver), I'm wondering whether this still applies when light inks come into the play and the driver needs to separate e.g. the cyan channel into dark cyan and light cyan. Is the sum of the dark and light cyan ink amounts still proportional to the cyan colorant value sent to the driver then? If not, we have lost again... Regards, Gerhard