# Characterization of Prints Based on Microscale Image Analysis of Dot Patterns
## 4 Experimental Results  
The efficiency of the dot segmentation method was evaluated by visual evaluation, meanwhile the accuracy of some computed values (size of the major and minor axis, area, radius of the circumscribe circle) was evaluated using the software ScopeImage 9.0. The computed values reported in Tables 1-3 are coherent with measurement values. The problem of threshold methods evaluation and comparison is discussed in [5], meanwhile the problem of shape measurements calibration is discussed in [6]. In our study, the objective was only to make a relative comparison of computed values between print samples. The accuracy of the computations was secondary.  
From Table 1 we can draw several observations:  
* Samples corresponding to samples number 1, 2, 3, 4, 5 and 6 are very similar in terms of dots shape. As most of the dots are circular, the parameter \"orientation\" is irrelevant (its standard deviation is very high).
* Samples corresponding to samples number 1, 2, 3, 4, and 5 are very similar (high proportion of doughnuts), meanwhile sample corresponding to sample number 6 is unique (in comparison with these samples) as a significant proportion of its dots have a hole (low proportion of doughnuts).
* The threshold separating \"circular equivalent\" shapes from \"elliptic equivalent\" shapes associated with the parameter \"circularity\" is less robust than the parameter \"roundness\" which is more relevant to characterize the circularity of non-circle shapes such as the one \(\in\) ID1/ID2/ID3). As illustration, compare the \"circularity\" of the sample corresponding to sample number 3 (0.80) with the \"circularity\" of the sample corresponding to sample number 11 (0.81, see Table 2), these values are similar but visually dots of the first sample are more circular than the second one.
* The shape and size of dots of samples corresponding to samples number 1, 2, 3, 4, 5 and 6 is statistically quite homogeneous (standard deviation values are quite low, for example less than 10 \(\upmu\)m for the perimeter).  
From Table 2, we can draw several observations:  
Figure 13: Another example of results for a cyan print with a cell angle of 60\({}^{\circ}\). % of dots belonging to category ID1 (34%), ID2 (0%), ID3 (0%), ID4 (0%), ID5 (55%), ID6 (11%, most of them are at the border of the figure). There is no missing dot. In total, 62% of dots have an elliptic shape, while 25% of dots have an elongated shape (less than 1% has a circular shape).  
Samples corresponding to samples number 11, 12 and 13 (and also to sample number 17, see Table 3) are very similar in terms of dots shape, most of the dots have a \"elliptic equivalent\" shape oriented in the direction of the print (see Figure 14), which is coherent with the values computed for the parameter \"orientation\".
* The proportion of doughnuts is lower than for samples corresponding to samples number 1, 2, 3, 4, 5 and 6 (only 34% for samples number 11 and 12, and less than 8% for samples number 13 and 17). These doughnuts are less visible to the naked eye but are noticeable at microscopic scale. As there are less doughnuts in these samples the \"circularity\" parameter is more accurate (in the range between 0.81-0.86), which is coherent with an \"elliptic equivalent\" shape. On the other hand, the standard deviation of \"circularity\" values is higher (in the range 0.35-0.48), as the dot patterns are more heterogeneous. This is due to a higher standard deviation of the \"perimeter\" and of the \"area\" of the dots.  
Unfortunately, the amount of data and of rotogravure printers used in this preliminary study (4467 dot samples vs. two printers) are insufficient to precisely evaluate the accuracy and robustness of all dot pattern parameters proposed; nevertheless, the amount of data was sufficient to demonstrate the relevance of these parameters.  
In the next section, we compare the robustness of these parameters versus different printing systems.