[argyllcms] Re: A better way to measure paper white?

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sat, 31 Oct 2009 10:19:10 +1100

Ben Goren wrote:
Graeme, might it make sense to add an option to chartread that will remember each of those start / stop white values, average them all together, and replace every white patch in the chart with that value?

For strip type instruments you're right that paper gets measured
at the end of each row. The problem is that because the paper isn't
delineated by spacers, it's difficult to know what is valid paper
and what is not. Conceivably someone could read a strip such that
there is just a spacers width of white at the start and/or end,
and the normal patches would be read fine, but there wouldn't
be enough white for a valid reading. So some tricky heuristics would
be needed to try and figure out what is valid white and what is not,
and if it goes wrong, you've got a bodgy white value to mess the
profile up. (And this would only be possible with the i1pro and Munki).
So at the end of the day, it seems to simpler and more reliable to
put all the instruments on an equal footing, and only measure values
from formally defined patches.

[There are in fact bigger "white" problems to solve for input
 and display readings. For input targets taken with a camera the
 illumination may be uneven. For LCD displays, the brightness can
 change significantly as they warm up. It would be good to be able
 to measure extra whites in both of these cases and compensate
 the readings accordingly. ]

Good idea though.

Graeme Gill.

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