Hal V. Engel wrote:
I think the main consideration is that the total ink limit used for creating your targets and profiles should be slightly higher than the total ink limit setting used in gutenprint.
Hmm. I would have said the opposite! Generally there is no hard limit for ink levels in a printer, but at some point there will start to be negative effects such as clogging up of screen patterns, excessive drying time, smudging, or even ink running off the page. For Xerographic printers, there can be more catastrophic results such as paper or mechanism jams, excessive toner floating about and blocking sensors etc., but there is still a progression from "not as black/vivid as it could be" to "too much!". But my experience is that the device behavior being fed into the profile software should have a margin over the final chosen ink limit, otherwise the device behavior isn't being characterized sufficiently for accurate results, and is in fact being extrapolated. Usually the extrapolation isn't that good. [ You can explore this by creating a test chart with a low ink limit, and then looking at the resulting profile a values beyond that limit. ] So ideally any ink limit being imposed by the print driver, or by the test chart should exceed the final chosen ink limit imposed by colprof or collink, and my rule of thumb is 10%, but it should really be as large as is practical. In a fully flexible print driver the settings would be approached in stages. At the first level would be the per channel upper limit and gross linearisation, making sure that the limit errs on the side of not limiting the gamut. At the second level there would be a per channel calibration and finely tuned per channel upper limit. At the third level there would be characterizing the device, and the total ink limit chosen for the test chart and/or print driver would be chosen such that grossly bad effects such as ink run/jams are avoided, but erring on the side of not limiting the possible gamut. At the final level would be the finely chosen total limit imposed in the profile creation (B2A table/device link table).
ink limit (as set in gutenprint). In other words the gutenprint ink limts are to prevent the printer from using too much ink and the ink limits used in targen and colprof are to create profiles that use the full range available for the printer. Graeme is that correct?
I wouldn't have put it quite that way. "Using too much ink" is not a physical limit, but is a user choice, and so I wouldn't say that this is the reason for setting a gutenprint limit. Instead, a print driver limit should really be reflecting the practical limits of the device and protecting it from harm. Preference type choices such as running costs, screen clogging, drying time or achieved gamut should really be set at the point of maximum flexibility, which is after characterization and during profile/link creation. Graeme Gill.