The SCTV, the Spot Colour Tone Value, is a ratio of the colorimetric difference between the hue, the substrate and the solid tone.
SCTV uses L*a*b* as a basis, and in the best case also spectral data, and therefore works equally well with all spot colours, printing processes and papers and delivers a consistent result. When calibrating spot colours, SCTV reliably produces a result in which the 50 % hue of the colour is visually very close to the expected 50 % appearance.
In the past, defined target values for the tonal value were specified by tone value increase (TVI) depending on the printing process and substrate. ISO 12647-2:2015, for example, specifies 16% dot gain for CMYK on image printing and 22% dot gain for uncoated paper.
With SCTV, however, the target value for SCTV is the same as the colour tone value. A 50% tone value should have a measured value of 50%, all other tone values should also have their respective pedant. This means that SCTV is visually consistent, which is not the case with density-based approaches, and is therefore more suitable for spot colours.
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