Saturday, November 15, 2008

Visual Perception And Digital Photo Editing

Human vision is incredibly adaptive so you can see in bright sunlight on a ski-slope during mid-day and at night on the highway to drive home. But this adaptability being essentially automatic and subliminal can be a disadvantage because your perception of small brightness differences between screen and print is not obvious until the print becomes a physical reality that makes it apparent.

How this possibly occurs even if your display is calibrated and profiled is because although the display profile is referenced by Photoshop or other color managed applications, whatever the display values are, they are translated to the parameters defined by the workspace profile. In other words the high range of brightness values that characterizes an LCD display are interpolated into the color values dictated by the Adobe RGB (1998) workspace profile for instance, which is static, and then those values are actually displayed in that longer brightness range of the LCD display, and nothing in calibration and profiling reflects the value differential and difference in midtone value that could be passed on through to a printer driver and printer profile in the process of making a print.

So that is where the Output Transfer adjustment function to produce a perceptually brighter print comes in I have suggested, or the alternative of incorporating the correction in a custom printer profile.The fact the midtone setting is based on the longer brightness range of the LCD rather than the shorter range for accurate print output has to be has to be estimated and assmed to adjust output manually. The alternate suggested custom profile for output brightness correction of course is a relatively expensive and sophisticated solution that is an advantage because it will work for all photographers who use Elements, Lightroom. Aperture or iPhoto and do not have Adobe Photoshop CS’ Output Transfer to adjust print brightness to print from.

What I have really said is that human visual perception is individually adaptive and therefor dynamic, but a color managed digital photo editing and processing system is essentially static and is not capable of accommodating the relative brightness range difference between LCD displays and print output. The result is the “ubiquitous” problem “my prints are too dark”, often caused by the brightness range of LCD displays influencing misplacement of the midtone setting to effect printing. So it should be evident the solution is to make the Color Management system dynamic and capable of sensing the differential between display brightness range and print output potential so the output matches the screen’s expectation of what the print should look like. Unfortunately that would demand a major overhaul of the ICC color management structure standards, and is not likely to happen anytime soon if at all.

The alternative is to get application software companies to recognize the problem and introduce an adjustment like the Output Transfer function that is more direct and as easy as an adjustment slider in the Print dialogue to facilitate making the print output lighter or darker. An adjunct to a slider solution could be a much more sophisticated and accurate print preview in the Print dialogue window. That would make the adjustment process perceptual rather than trial and error, as is the case using the Output Transfer function. Of course I will do what I can to get such a software solution made available, but the more input from reader/users there is, the more weight there is in the balance in favor of making such a change.

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