Re: Dot gain in PS 6
Re: Dot gain in PS 6
- Subject: Re: Dot gain in PS 6
- From: Stephen Marsh <email@hidden>
- Date: Thu, 22 Nov 2001 17:23:46 +1100
Larry writes:
>
My question for this list, and especially anyone from Adobe lurking
>
around, is this still true for PS 6's separation algorithm?
Larry - since you are referring to the legacy built in custom CMYK of
Photoshop 6 (same as ver5 and _similar_ to previous versions), you can
and should choose the correct measured reading for your intended output.
If you measure the 50% colour bars in each ink every inch or so along
the edge of the press sheet, then average out these figures...then
reapeat the process from among the press run - say 10 times, at
different points in the run...then repeat the process for other types of
jobs on similar stock, then do this at different times of the
year...then you might be able to get a handle on the average gain for
this device (I am presuming an offset press).
All this for only the midpoint - if you want more control, perhaps
measure other tones as well with the same averaging process so that you
are not mislead. Sorry if this sounds obvious <g>, but a press is a very
different animal to fingerprint than a more stable device such as a
desktop inkjet printer.
You would plug in the averaged numbers that have been read into each of
the built in custom CMYK dot gain curves fields.
I doubt your many averaged measurements would indicate that you need to
factor in more dot gain for cyan than the other inks - but black would
have a lot of drift on an average A2 or larger press.
>
If I am
>
measuring dot gain with a densitometer of an actual press run to get
>
proper dot gain information, do I need to add 4 points onto my cyan
>
to avoid getting images that are too blue? One post seemed to
>
indicate this.
Regardless of what 'on the fly' built in custom CMYK profile dot gain
you are using (standard or curves) - the separation algorithm still
converts a neutral input value to a neutral output value, so you do not
need to second guess the separation algorithm!
The problem seems to be that when you first choose the curves dot gain
option - Photoshop defaults to placing more gain in the cyan sep. This
poor default is corrected by knowledgeable users, just like many other
poor default settings (in Adobe or any software).
Whether you change this default or not, the sep is still neutral (if the
input is). It's just that the 'legacy' high setting confuses people.
P.S. Last time this came up on this list, it was recommended that a
personalised pre built profile would be best - generated from
hardware/software. True, this is probably the best way to get a handle
on both colour and tone - but if all you have is a good reflective
densitometer and Photoshop, then you can try to make the best of the
'free' tools in your posession. If you can't get the inkset measured -
separate to a standard for your printing process (Film proof, SWOP,
GRACOL etc), but at least you can get the dot gain customised. I say go
for it, when done correctly it cant hurt!
Hope this helps,
Stephen Marsh.