Discussion: View Thread

Dear all,

I would like to have a clarification related to wDeltaL in G7 evaluation method, in particular related to the software and instrument data showed.

Why this value is always Positive? it cannot be more useful have the negative and positive value to better understand the direction of the error in tonality?

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Luca Morandi

ColorConsulting Srl
Saronno
+393497614700
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Great question! w∆L is always positive because it shows magnitude, not direction. If it included positive and negative values, it would represent Delta L from the NPDC baseline rather than a weighted deviation.

I really like your idea as an additional indicator-it could help fine-tune mechanical press adjustments and assist operators in making more precise density corrections. If NPDC is too light or dark, the fix should target gray balance. For example, if NPDC is too low and gray leans green, adding magenta would neutralize the cast while increasing NPDC.

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Timothy Quinn
Consultant
Nazdar Consulting Services
Shawnee KS
816-582-6748
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Hi Timothy, I completely agree with your point. Moreover, the weighted deviation can also be positive or negative, and it indicates both the magnitude and the direction

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Luca Morandi
Process Calibration & Brand Owner Mgr.
ColorConsulting Srl
Saronno
+393497614700
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Original Message:
Sent: 03-13-2025 08:25 AM
From: Timothy Quinn
Subject: wDeltaL

Great question! w∆L is always positive because it shows magnitude, not direction. If it included positive and negative values, it would represent Delta L from the NPDC baseline rather than a weighted deviation.

I really like your idea as an additional indicator-it could help fine-tune mechanical press adjustments and assist operators in making more precise density corrections. If NPDC is too light or dark, the fix should target gray balance. For example, if NPDC is too low and gray leans green, adding magenta would neutralize the cast while increasing NPDC.

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Timothy Quinn
Consultant
Nazdar Consulting Services
Shawnee KS
816-582-6748
------------------------------

The reason is that this is a tolerance, not guidance, and it is equally bad to be too dark or too light, too red or too green and the unacceptability is equal in both directions, for simplicity. I just received an evaluation report from a German consultancy that indeed indicated direction in addition to magnitude. Process control software always indicates both, but that is for guidance. A G7 qualification is only a pass-fail system; it is not intended as an instruction for improvement. 

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Mike Strickler
MSP Graphic Services
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Original Message:
Sent: 03-13-2025 08:25 AM
From: Timothy Quinn
Subject: wDeltaL

Great question! w∆L is always positive because it shows magnitude, not direction. If it included positive and negative values, it would represent Delta L from the NPDC baseline rather than a weighted deviation.

I really like your idea as an additional indicator-it could help fine-tune mechanical press adjustments and assist operators in making more precise density corrections. If NPDC is too light or dark, the fix should target gray balance. For example, if NPDC is too low and gray leans green, adding magenta would neutralize the cast while increasing NPDC.

------------------------------
Timothy Quinn
Consultant
Nazdar Consulting Services
Shawnee KS
816-582-6748
------------------------------