Saturday, January 3, 2009


Have you ever blown through a red light in your car, and as soon as you got through the intersection you realized what you had just done? Other than worrying about whether a cop saw what you did, you may have realized that your eyes saw the red light, but your mind did not register the perception and respond as usual so you could stop and wait for the light to change. What this kind of incident illustrates is that human vision is made up of two distinct functions, what our eyes see and what our mind perceives. As well as a third factor memory, which allows us to not pay conscious attention to everything familiar our eyes see in the course of daily activities, otherwise we would never get anything accomplished if we had to consciously deal with everything in our vision familiar or not.

So what does this have to do with photography and any current digital problems like “prints too dark”? Back in the 70’s an intense interest in Ansel Adams Zone system was appended by Adam’s stress on “visualization” as a way to exercise some control between perception and a predictable photographic result. Around the same time Richard D. Zakia at RIT published a book of articles and scientific papers called Perception and Photography that was rather widely read providing a more modern understanding of human vision and how it can be more successfully employed as part of the process of making effective photographs and controlling the performance of the media. Thirty some year later perception has a somewhat different photographic role and even more important imaging function with photographs that are the result of what is done visually on-screen to edit and manipulate the attributes of a photograph in applications like Photoshop. Which brings us to the current problem of a mismatch in density or image brightness between what is seen on-screen and sometimes in a very different, too dark, print result.

That there is a problem today is due, in large part, to the introduction of very much brighter LCD displays compared to the CRT’s monitors that preceded them. What is perceived on screen does not match what results in a print in density, even though in a color managed workflow the colors seen on screen can be accurately reproduced in a print quite reliably. It should be noted here that digital camera JPEG images adjusted by a camera’s post exposure processing, if just opened in a computer and printed without editing, will very likely NOT suffer the “prints too dark” problem. So the only sure way the LCD brightness problem will result in print darkness is if the image is edited by PERCEPTUAL adjustment for brightness on-screen with an LCD and the file is then saved and printed.

Sometimes just reading the data and coming to conclusions on the basis of the fact an LCD display, even when optimally calibrated and profiled to a brightness luminance of 120.0 CD/m2, compared to the lower range of a typical CRT monitor with an average white point luminance of 90.0 CD/m2 (which did not induce “prints too dark”), is not totally convincing nor entirely complete evidence. So, fortunately for this research, I had a very good Sony Trinitron 520 Pro model 21” CRT stored for the last 3 years and after only a couple of years of use. And it just happens my Mac Pro will run two different kinds of displays in mirrored mode with both having the same signal image on-screen, as well as both being individually and independently calibrated and profiled. So after some digging in my closet I dragged out that 100 pound monster and set it up beside my NEC Multisync 2090 UXi LCD display. Both screens happen to be the same measured size, but once turned on and warmed up they do look very, very different and it is not just the NEC LCD display is a bit brighter. There really is not that much brightness difference as the Sony 520 CRT produces a maximum white point density on the high side at 97.0 CD/m2 compared to my LCD sitting next to it at 120.0 CD/m2.

Even though both were calibrated and profiled to the same aim points of a color temperature of 6500K and a gamma of 2.2, there was a difference in perceived contrast that looked higher in addition to greater brightness of the of the LCD, but what was really surprising was after precise calibration and profiling the neutral gray of the two displays looked very different, with the Sony CRT appearing to be warmer and less neutral than the NEC LCD. In other words they measure the same but look different, which may be due to a difference in light frequency and modulation because of the distinctly different light sources involved. The bottom line is that not just brightness but every visually apparent factor will affect and influence perceptual image editing adjustment between the two kinds of display, and the resulting images will reflect some of that difference. I think in my case when I switched to LCD’s from CRT’s I was consciously aware a perceptual accommodation was needed and I altered my image editing accordingly, because my print output was pretty consistent. However, I do my own custom printer profiles and I did make some print density adjustments in the printer profiles I produced in the las 2-3 years I have been using LCD displays.

Although it would resolve the prints too dark problem, would I want to go back to CRT monitors if they were still made? Not on your life, because LCD’s provide a more neutral gray, greater internal light and color contrast to reveal tone differences and easier editing, and at least my LCD’s are much sharper than any CRT I had used in the past. So let’s hope for a print brightness fix and keep the LCD’s!

No comments:

Post a Comment

You can also ask questions I will answer privately by sending me an e-mail at: