We formed our own (subjective) opinions of the various sequences but were then fortunate that FESPA Slovakia were holding a meeting at which Bill Appleton was speaking. The experienced Slovakian printers gave their own opinions. There was, of course, no agreement about which sequence was best, though sequence 5 and one of the Caza sequences had their supporters. Preferences depended, not surprisingly, on what people were looking for. As we will see, the 15° moiré effect strongly biased many of the judgements. As this effect can be taken into account by a very simple process we will ignore this aspect of the prints till we come to the section devoted specifically to the effect. Rather than rely on subjectivity, we decided to create an objective measure which we call the Colour Fidelity Index, CFI. This captures 3 independent factors, all of which have to be right: • Good greys –shifts in greys are a good indication of a print generally out of control • Good 3-colour tones – this captures the fact that a lot of the subjective colour judgement was based on the more complex tones which often looked far too dark. • Good shadows – we want to lose as little shadow detail as possible. We had anticipated (because of other work done at Swansea) using a fourth criterion – the colour gamut. But careful Lab
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This portion of one of the Linotype-Hell test images shows the wide colour variation from four of the eight test sequences. Clockwise from the top left, 4:MCYK, 5:MYCK, 6:YCMK, 8:CMKY
measurements and plots on the CIE chart showed that there was no significant difference in gamut in any of the sequences. We have no explanation for why our results differed from Swansea’s and others might like to include gamut in their own CFI. The idea was to obtain objective measures for each of these factors, scale each of them from 0 100 then divide the total by 3 to give us a 0 100 CFI, where 100 is the perfect print. Getting the objective measure for the greys was easy. For a 20%, 50% and 90%