articles/Nature/scoreandperformance-page5

The Score and the Performance - part 5 of 1 2 3 4 5 6

Published 01/08/2010

Soft Proofing for Monochrome - Is it Possible

A few things came together to make this couple of pages possible. We stumbled across the Eric Chan icc profiles for ABW (see previous issue's barytas article), we had some discussions with Simon Prais at Colour Confidence and finally we had in front of us a freshly Fogra-certified, quality monitor. In theory, at least, we should have been in a position to do some accurate soft proofing.

Monochrome proofing is different to colour proofing. Normally you are looking for a colour match between either two print samples (say press and proofer output) or between a screen and a print. Variations in luminance may be masked by variations or similarities in hue and saturation when viewing colour. When it comes to monochrome (and assuming you do not have a colour-biased print) the only thing you have to go on is the monochrome luminance - quite a difficult proposition.

Initially we found it difficult to discern differences between two soft-proofed views, one proofed to a bespoke colour profile and the other to an Eric Chan monochrome, ABW profile. We therefore devised the following test and had four people participate in the trials. The tests were carried out 'blind', that is all the testers worked by viewing just the print and the soft-proofed screen view; they were unable to see the numerical values of their adjustments as they made them using either sliders or arrow keys to ratchet the values up and down. We applied either a curve, HSB move or levels adjustment, as appropriate, to vary the luminance of the print, its gamma value (in Levels) or the bow of the curve.

Changing the curve proved to be too difficult to master without seeing the palette and so we ended up concentrating on just the HSB Brightness slider and the gamma of the Levels dialogue. The testers were presented with a very dark or very light screen image and asked to adjust the values until they felt that the screen soft proof matched the print standing in a viewing booth. The viewing booth was set at 2,000 lux and 5300°K; tests outside the viewing booth were in mixed light of low strength. The screen was set at either 75, 80 or 160cd/m2, but mostly at 75cd/m2. A significant advantage of the ColorNavigator software from Eizo is that you can easily switch between profiles and thereby change the screen luminance.

An initial finding was that the testers improved dramatically, both in speed of adjustment and accuracy, in the first few attempts. One tester dropped from an initial error of 17 points down to consistent errors centred around ±2 points over 10 attempts. The quality of the viewing environment also had an influence; darker viewing was related to darker judgement settings. The initial errors were eliminated from some of the statistical analysis.

Using a correct illumination viewing booth, the testers' results varied both above and below the correct luminance value suggesting that errors were in judgement, not a bias in the viewing conditions - if, for example, the viewing conditions had been too bright we would have expected errors biased in that direction. The judgement errors varied between ±7 points in brightness value equivalent to -10RGB points and +6RGB points (ie a 16 RGB points variation). To put some perspective on this value we print the target here, set up at ±5 points and ±12 points so you can see the difference.

• The Score and the Performance page 1
  
• The Score and the Performance page 2
  
• The Score and the Performance page 3
  
• The Score and the Performance page 4
  
• The Score and the Performance page 5
  
• The Score and the Performance page 6
  

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