Perceptual Adaptation: Undershooting and Overshooting Values

perception
value
valuejudgement
adaptation

(Anthony Waichulis) #1

While many seemed to enjoy my recent post on the role of perceptual adaptation in “overshooting” reflected lights—it is also important to keep in mind that the same mechanisms can lead to significant “undershoots” in very light regions. As such, I would like to share some thoughts on adaption awareness and intentional under/over-shoots in regard to viewing distance, optimal definition, and communicative efficacy.

For anyone that has ever studied photography, you are probably already familiar with the “exposure triangle” which contains as components shutter speed (measured in fractions of a second), aperture (f-stops), and film speed (or ISO rating, which is the level of sensitivity of the sensor or film). “Cambridge in Color” offers a great analogy for understanding exposure: “Achieving the correct exposure is a lot like collecting rain in a bucket. While the rate of rainfall is uncontrollable, three factors remain under your control: the bucket’s width, the duration you leave it in the rain, and the quantity of rain you want to collect. You just need to ensure you don’t collect too little (“underexposed”), but that you also don’t collect too much (“overexposed”).” The key, however, is knowing which setting/trade-off to choose, since each component setting also influences other image properties. For example, aperture affects depth of field, shutter speed affects motion blur, and film speed affects image granularity.

Like the quest to find the optimum exposure triangle for photographers, particular aspects of observational representationalist drawing and painting efforts require adjustment that also carry both advantage and disadvantage. Let’s look at one of these problems, one related to “value undershoots”, and see how “our own settings” can significantly impact the work.

For example, an initial glance at this simple still life setup from about 5-7 feet away yields an percept (IMAGE A) that results in the very light shell on the right nearly devoid of any surface structure (very near “blown-out”). There is a very slight gradation from the shadow side up towards the light before disappearing into a sea of bright, glowing white. However, as I sit closer and fixate on the shell, my vision begins to adapt to the light level, and more surface values and variations become visible (IMAGE B).

Quickly, my mind beings to consider the following questions:

1. Do I try to maintain the bright, significant crescendo of white describing the shell that I experienced upon first glance? (This will result in a great punch of contrast which can often facilitate successful communication over a subject over longer distances. However, surface information in the lightest regions here will be sacrificed resulting in a potential information void when the work is examined at very intimate proximities.)

2. Should I substitute the perceived value range of a single object that arises from one perceptual adaptation for another? (This might seem like a common-sense compromise—however this can often lead to an overall diminishment of global contrast and skew some value relationships, thus resulting in a diminishment of communication distance and overall form.) (IMAGE C)

3. Do I try to shift everything to find an “exposure” that maintains observable relationships when viewing the whole but allows for evenly distributed/diminished form and/or surface information? (This is also a viable choice, however doing so may result in some non-linear comparisons that are very difficult to keep track of and will often carry the cost of information-loss somewhere along the lightness continuum.) (IMAGE D)

Now I have spent the better part of my career working on the right balance of value overshoots, undershoots, substitutions and alignments that would hopefully yield an effective visual communication, maintaining a desired level of definition over a particular range of viewing distances.

So, based on your own representationalist goals, how do you determine the right balance of these considerations for yourself?


(John Livesey) #2

The varying of exposure to expose more detail in the bright and shadow areas is pretty much HDR photography. Looks really detailed and intense and pretty cool but not natural and not particularly restful to the eyes. Probably as our brains know it is not what we would naturally perceive based on a lifetime of training our eyes with our biological limitations. So I’d say cool, alter exposure a little either way but don’t got to far or it will look stylised and unnatural. Unless of course that is what the artist is after.


(Nanci France-Vaz) #3

Such a great topic and I always battle that as well as all of us🙂

I find, for me, it all depends on the mood I’m trying to communicate. Sometimes I want it to be about the form, and in that case I am searching for a strong middle or dark middle to set up my focus point. I used to use dark backgrounds and that works well as you have a stronger simultaneous contrast setup. I find that easier to problem solve instead of light environments. Those are more challenging and if you have an undershoot then they can all merge together and…tricky. If you over expose anything… you loose the quality of the light.
Sooooo, my usual way to handle this sort of problem is temperature changes and edges. Sharp edges give the illusion of more light and softer edges make the subject appear to drop off more gradually, lower values without lowering the value. Two go to methods for me. The warm and cool method allows you to keep values close but get form from your subject. You maintain the atmospheric quality. I.e.: Bougereau flestones, Van Dyck was a genius at this, and Paxton as well.

I’m curious to read how others handle this.


(John McCuin) #4

“lower values without lowering value”

Nanci, would you mind explaining to me what you meant by this, just so I know that I understand you correctly?

Regarding warm/cool method, could you post an image example of what you mean? I’m assuming you mean variations in adjacent color regions that are close in value but oscillate in hue between warmer and cooler, and that this practice will help turn the form without much change in value. Am I understanding you correctly?

Thanks!


(Nanci France-Vaz) #5

That’s exactly right John…I use close values and temperature changes when I do portraits or figures. You could also dobthis with still life. Basically it is broken color changes and mosaic patterns.

If you go to my website there are quite a few.

Here’s a good example of a figurative piece. The. background was a drape I had and I used a warm and cool light juxtaposed. The values are close in her hands and face on our right and the dress as well. But it turns. I used warm lights and cool shadows in this.
The cooler one is daylight… northlight that bring the bottom image. The first image is lighting in my house which would be gallery light. It had to work in all light with the close values and a dark background.


(John McCuin) #6

Thanks for the great feedback on your process. Very beautiful painting!


(Nanci France-Vaz) #7

Thanks John:blush: