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Static Versus Dynamic Image Quality

© 2006 KenRockwell.com

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Static and Dynamic image quality are very different ways of measuring image quality.

Static image quality is what's measured in the sterile confines of a laboratory.

Dynamic Image Quality is what matters in actual photography, but much harder to measure.

I'm going to explain the differences so hopefully you'll put more emphasis on your own photographs and eyes and less on camera-company sponsored websites and magazines loaded with exacting measurements of unimportant qualities.

Want to know how good a camera, film or lens is? Simple: go shoot with it and look at the results! Don't waste your creative time fretting over reviews that try to put numbers on everything. None of use can see differences in images made by cameras with measured quality numbers that differ by less than about 40%!

Static Image Quality (SIQ)

Static Image Quality (SIQ) is what's measured in a laboratory, like resolution or noise. It's the performance you can get when nothing about the subject is changing and you have all the time in the world to read the manual, find hidden buttons and twiddle around optimizing settings.

Static Image Quality is easy to measure by just about anyone following a script in a lab. It requires only minimal photographic skill, and merely needs to be set up by someone with a modicum of lab ability.

Static Image Quality is what you read in published camera test reports loaded with facts and figures. Once a test procedure is defined it's trivial for anyone working at that magazine or website to churn any new camera through the same set of tests and spew out reams of the same facts and figures.

Unfortunately all this detail applies to a set of conditions which rarely, if ever, applies to the photographs you or I ever actually make.

Static Image Quality has little to do with the Dynamic Image Quality one actually gets when photographing in the field.

Static Image quality gives no consideration to the real world which is constantly changing and rarely conforms to standard settings. For instance, in a lab you can create a perfect 5,400K daylight, but you never get that in practice.

Static measurements include measurements of dynamic qualities like autofocus speed. These are easy to measure in a lab; you just set it up and time it. Don't confuse static measurements of dynamic qualities with Dynamic Image Quality itself. Even for focus the far more important measurement of how well the camera hands off among the various AF zones tracking a moving soccer player moving across the finder is something no one bothers to try to measure. It's too tough.

See also Fallacies of Lab Noise Measurements, a separate article.

Dynamic Image Quality (d-IQTM and DIQTM)

Dynamic Image Quality (d-IQTM and DIQTM) is the performance one gets in the real world photographing things worth photographing and then looking at the pictures. of course this takes a trained, skilled eye and costs more time and money than simple lab tests.

The real world is constantly changing. Light outdoors changes not just from minute to minute, but from second to second. One must be able to adjust a camera to optimize exposure and white balance on the fly, without having to grope through menus. Cameras need to have the correct range of adjustments. For instance, many digital cameras omit the critical Shade white balance setting, which is required most of the time outdoors unless one is in direct sunlight.

Some cameras' defaults may or may not be more relevant to the real world than laboratory conditions. For instance, daylight settings are usually similar, but there is no standard for shade, and complete mayhem and disarray among cameras when comparing fluorescent white balances.

Even in a studio setting you have to contend with your subject changing. Portrait subjects move, their makeup needs to be updated as they perspire and of course children never sit still. Food congeals, ice cream melts and flowers wilt. About the only real-world situation that's stable is photographing inanimate objects in a studio with carefully fixed and regulated lighting. In those cases you approach static conditions.

Because everything changes all the time, the quality of an image is more often related to how deftly one can maneuver about the controls of a camera than any abilities that camera has in a laboratory. For instance, in landscape photography one needs to be able to pick up a camera and haul it over and set it up at a new location quickly as the light moves around at sunset.

Dynamic Image Quality can't be measured in a lab and it can't be measured quickly.

Dynamic Image Quality is measured by a skilled photographer as he photographs many different things in the real world. Dynamic Image Quality is measured simply by looking at the resulting images image and applying wisdom acquired over decades of photographing.

Wisdom is knowledge multiplied by many decades of experience. Wisdom allows seeing beyond short-term fads. Wisdom permits purely visual evaluations without retreating to numeric crutches. This is art, and of course personal biases will favor one look or another. For instance, I prefer wet-look glossy prints for their superior blacks and the better contrast I can get on those papers. Other people just look at numbers for printing test charts and are happy with ink jet prints, which never even get decent gloss and to me look awful compared to real prints.

I'm a photographer, not a lab, and always address Dynamic Image Quality in my reviews. Some may prefer reams of static measurements, and they can get those just about everywhere. Likewise, places that publish static measurements can run as many cameras as the manufacturers throw at them through their canned tests.

I spend a lot of time using any given piece of gear in my normal course of photographing. That's why I can give such insight and enlightenment into the subtle nuances of equipment's performance. It's also why I can't possibly report on every product under the sun. I make my level of intimacy very clear in my reports. Some things I own, in which case I post more detail than most people ever want, or maybe I'm just making a critical analysis of a press release, which means little, or something in between. Sadly many reviews published elsewhere are little more than rewrites of press releases, but they don't tell you that.

Meaningful measurements of image quality come from skilled photographers. They know what's important and what may be ignored. That's why I caution people from paying too much attention to splitting silly details like noise and resolution measurements. I'm just doing this to help out people who enjoy photographing as I do, not trying to crank out as many reports as possible.

A Story from Hollywood

I was at a camera shoot-out in Hollywood. We were comparing several $250,000 HDTV cameras. The salesmen from each camera company set up all sorts of static test charts as well as little moving setups to track motion and everything one could imagine.

The guy making the purchasing decision knew every camera would do about the same shooting the charts. Each camera might have 10 or 20 % difference in one parameter or another when measured with instruments. The salesmen and engineers would argue endlessly about this. Unfortunately we can't even see a 20% difference in resolution with real subjects. Our decision maker was humoring the salespeople as if he was actually interested. Actually he was ignoring this circus of measurebation as far as his choice was concerned.

This studio knew that their cameramen could get the same look from any of these cameras after they tweaked them enough. The choice was made based on which camera could be set up (tweaked) the quickest , and could it get the subjective artistic look they wanted. The key elements were how fast and easy was it to get to these adjustments, and were the correct adjustments even on the camera!

This is exactly what I tell you people when you're shopping for $250, $2,500 or $25,000 digital cameras, all of which are cheap compared to what I used to work with in Hollywood. The important differences are in the controls, how easy they are to get to and manipulate, and whether the right controls are there. For instance, some cameras hide critical adjustments under menus instead of having direct buttons, and some critical things, like the ability to tweak each and every WB preset, are simply missing in some cameras. This is what defines image quality, not resolution.

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