dhenry:
with 16-bit resolution, ...
have 32-bit resolution for light intensity.A couple of questions:
- What kind of eyes do you have that require that kind of resolution?
- What kind of computing power is required for that kind of resolution?
- 32-bit resolution would give me 4.29 x 10^9 levels, thus around 9.6 log levels of light intensity which would be little less than normal ambient light levels experienced by humans [1]. So when designing a visual stimulator like that one for example in optimal case you would like to have the whole ambient light level intensity under electronic control and not having to play with neutral density filters for example. For example, using the same system when the subject is light-adapted and after full dark adaptation when retinal sensitivity is significantly increased [2].
[edit] So if you would only want a normal operating range of 256 intensity levels (8-bit) your retinal sensitivity would have increased around 4 log units during full dark adaptation (~45 minutes in full darkness, Light and Dark Adaptation by Michael Kalloniatis and Charles Luu – Webvision) then it would not be possible at all to have the same operating range of 256 intensity levels in this new condition without using attenuating filters such as normal neutral density (ND) filters. That is why the high dynamic range was desired initially.
So the work by Demontis et al. [3] for example gave ~4.5 log units of resolution which is kinda nice for most of the applications, but if you would start modulating the output with a sinusoidal or other waveform envelope [e.g. 4], a little leeway could be nice.
[1] Fain, G L, H R Matthews, M C Cornwall, and Y Koutalos. “Adaptation in Vertebrate Photoreceptors.” Physiological Reviews 81, no. 1 (January 2001): 117–151. Adaptation in vertebrate photoreceptors - PubMed
[2] Lamb, T. D., and E. N. Pugh. “Dark Adaptation and the Retinoid Cycle of Vision.” Progress in Retinal and Eye Research 23, no. 3 (May 2004): 307–380. http://dx.doi.org/10.1016/j.preteyeres.2004.03.001.
[3] Demontis, Gian Carlo, Andrea Sbrana, Claudia Gargini, and Luigi Cervetto. “A Simple and Inexpensive Light Source for Research in Visual Neuroscience.” Journal of Neuroscience Methods 146, no. 1 (July 15, 2005): 13–21. http://dx.doi.org/10.1016/j.jneumeth.2005.01.007.
[4] Gooley, Joshua J., Ivan Ho Mien, Melissa A. St Hilaire, Sing-Chen Yeo, Eric Chern-Pin Chua, Eliza van Reen, Catherine J. Hanley, Joseph T. Hull, Charles A. Czeisler, and Steven W. Lockley. “Melanopsin and Rod–Cone Photoreceptors Play Different Roles in Mediating Pupillary Light Responses During Exposure to Continuous Light in Humans.” The Journal of Neuroscience 32, no. 41 (October 10, 2012): 14242–14253. http://dx.doi.org/10.1523/JNEUROSCI.1321-12.2012.
- Computing power meaning what exactly in this context? I could control a LED driver with DMX input and DC output with 16-bit resolution using a DMX shield and then switch that with a Uno32's 16-bit PWM for example so not very special hardware would be required
DVDdoug:
Uh... Yeah.... Dynamic range is the difference between full-bright and fully-dark. You can't get any more dark than "off", so you can only go brighter ... and you can't (or shouldn't) go over the device's maximum current rating on the bright-end.16-bits (converted to decimal) gives you a range from 0 to 65,535. I'm sure you can't tell the brightness-difference difference between 0 and 1, between 65,534 and 65,535, or between 30,000 and 30,001, etc.!
So maybe I was not specific-enough about the application so it would be for a generic-purpose visual stimulator to be used in vision research. So I agree that in general the difference that you mentioned would not be of a huge aesthetic difference but especially if you start using the system with other species than humans, the same logic might not apply anymore.