Calculation Methods for Tone Value Curves

In GMG OpenColor, make sure to use the same calculation method that is used at the printing press to ensure a print-to-proof match.

The two calculation methods are not compatible with each other. If you have imported or created a gradation curve based on the Murray-Davies equation, you cannot simply change it to SCTV in GMG OpenColor. If you want to use an SCTV curve, you will have to import SCTV data or create a new curve. However, GMG OpenColor allows you to view a Murray-Davies curve in SCTV mode and vice versa, so that you can see how it would look like.

Switching the Calculation Method from Murray-Davies (MD) to Spot Color Tone Value (SCTV) in the Color Corrections dialog box is possible only if the spot color characterization includes tint values and if no correction has been applied so far. This means, if either a gradation curve was loaded as a correction curve or if the calculated gradation curve was edited manually, the Calculation Method drop-down list will be disabled. This also means that if you are using a factory-default GMG spot color library such as PANTONE PLUS, the Calculation Method drop-down list will be disabled, as these libraries include only full tone values. However, you can load a custom gradation curve created with the Spot Color Tone Value (SCTV) calculation method to use the new method for these spot colors.

Available options:

• Spot Color Tone Value (SCTV): 
  ISO 20654:2017 defines a metric for assessing intermediate tones of a spot ink. Instead of density, it works based on color measurements. It is able to produce approximately uniform visual spacing of tones between substrate and solid.
• Murray-Davies (MD):
  The Murray-Davies equation. is a traditional method to calculate tone values of CMYK inks from density measurements. This method has its limitations when it is applied to spot inks.