ISO 20654:2017定义了一种用于评估spot油墨中间色调的指标。这种计算专色色调值（SCTV）的方法可以在基底和固体之间产生近似均匀的色调视觉间距。它可以通过固体油墨、基材和一块或多块待测中间色调的光谱反射率或色度测量值计算得出。

ISO 20654:2017 defines a metric for assessing intermediate tones of a spot ink. This method for the calculation of Spot Colour Tone Value (SCTV) produces approximately uniform visual spacing of tones between substrate and solid. It can be calculated from spectral reflectance or colorimetric measurements of the solid ink, substrate and one or more patches of intermediate tones to be measured.