Re: Newsprint G7 calibration
Re: Newsprint G7 calibration
- Subject: Re: Newsprint G7 calibration
- From: Steve Upton <email@hidden>
- Date: Sat, 24 Mar 2007 19:01:14 -0700
At 3:34 PM -0400 3/24/07, Bill Birkett wrote:
>Roger-
>
>The G7 methodology defines the solid overprint of C, M and Y to be perfectly neutral (NPDC).
Whoa! hang on here. The G7 methodology does not, in any way, define the solid overprint of C, M and Y.
Also, it does not strictly define the neutrality of 50,40,40. It suggests defining it as a*=0 and b*=-2 but you can also define neutral point yourself if you like. This helps with papers that are a different white point, or simply personal choice.
Remember G7 is a press curving technique. It is not intended to only let you hit ISO 12647-2. It is helpful for hitting ISO but can also be used outside ISO if desired.
>When that isn't the case (which is most of the time), 100% C, M and Y will map to some other values. This is very likely the cause of the problem you encountered.
No!
Because G7 (and any curving process) only controls individual channel behavior and not inter-channel behavior, it does not affect 100% patches and also cannot affect the color of 100/100/100 CMY..... OK so that's not 100% correct. G7 does control inter-channel behavior in the neutrals, but only the neutrals and not at max densities. If you want to control inter-channel behavior beyond that you are talking about color management and need ICC profiles.
This is good. If it did, you'd find that any limit to any channel would reduce the overall gamut of the device. Nasty!
One of the strengths of G7, that I think confuses people sometimes, is that it can scale to the density range of the printing system. This means that
If, in using the G7 process or IDEALink software you find that the resulting curves have anything less than 100% for the maximum value in each channel you have discovered a bug or have not implemented the technique correctly.
>
>Curves based on TVI avoid this problem, since 100% always maps to 100%.
No different than G7. Ever.
>If you want to use the NPDC idea, the best approach is to make two sets of curves, one using NPDC and the other using TVI. Then, blend these curves together, with 100% NPDC and 0% TVI in the highlights, changing smoothly to 0% NPDC and 100% TVI in the shadows. This will give you control of gray balance in the highlights and midtones, where it matters, while preserving the integrity of the shadows.
This seems like needlessly complicating things but I could see how there might be some value in it for some specific work-around cases. Overall G7 should give very similar results to TVI (and has been proven to do so). It just prioritizes gray balance over raw TVI behavior, which I personally think has value as so does our eye.
But when comparing the systems, let's make sure we are doing it with the correct information.
Regards,
Steve
________________________________________________________________________
o Steve Upton CHROMiX www.chromix.com
o (hueman) 866.CHROMiX
o email@hidden 206.985.6837
o ColorGear ColorThink ColorValet ColorSmarts ProfileCentral
________________________________________________________________________
--
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Colorsync-users mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden