What is  ISO/TS 18621-21:2020 about?  
 ISO/TS 1862121 defines a measurement method for the evaluation of distortions in the macroscopic uniformity of printed areas that are oriented in the horizontal and vertical direction, such as streaks and bands.
ISO/TS 18621-21 provides requirements for the layout of the test form, the use of a colour measurement device taking measurements in a 2D sampling grid, and the formula to compute the Macro-Uniformity-Score.
ISO/TS 1862121 does not cover any non-adjacent or non-horizontal or vertical patterns. Due to the used spatial frequency, the Macro-Uniformity-Score does not measure high frequency (fine) patterns such as missing nozzles. 
Who is ISO/TS 1862121 for? 
ISO/TS 18621-21 on Image quality evaluation methods for printed matter is useful for: 
- Printing manufacturers
- Microscopic printing quality assessors
- Macro-Uniformity analysts
Why should you use ISO/TS 1862121?  
The subject of image quality is broad and complex, due to its multidimensionality and the apparent characteristics of human vision. Many different methods can be available to provide a measure of a particular visual attribute in some particular viewing context and aimed at a particular printing technology. 
ISO/TS 1862121 focuses on the macroscopic uniformity that exhibits 1D type patterns that extend more or less across the printed area of a page. It uses well-established colour measurement instruments as the basic measurement device, especially systems that can be combined with automated XY-tables for performing well-defined measurements in a complete 2D grid of measurement locations in an easy way. These systems generally have a minimum pitch in both dimensions of 6 mm. This method takes a much more rigorous approach than the 9-point sample method that is defined in ISO 126477 that is applicable to proofing systems.
ISO/TS 18621-21 describes a methodology in such a way that other documents can apply it for specific use cases. Such documents will typically need to apply additional constraints on test pages and process control in order to ensure that the resulting Macro-Uniformity-Score can be compared between different printing devices, substrates, and ink sets.
