[visionegg] Stimulus brightness vs. background brightness
- From: Martin Spacek <mspacek@xxxxxxxxxxxxxxx>
- To: visionegg@xxxxxxxxxxxxx
- Date: Mon, 07 Feb 2005 01:37:56 -0800
Hello everyone,
I've noticed that if I set both the brightness of a target and the
brightness of the screen background to be 0.1, I can still faintly
distinguish the target from the background (the target is slightly
darker). This isn't the case if I set them both to 0.099 or 0.11. Has
anyone else noticed this? Is this some kind of roundoff error, where the
value for the target is rounding off in a different way from the value
of the background?
Specifically, I've set the target and background colours to be both
(0.1,0.1,0.1,1.0) (RGBA). Changing the alpha for either one doesn't seem
to have an affect. I've tried this on a couple of different Win2K
machines, VisionEgg reports 32 bit colour on both. I'm not sure if there
are other special greyscale brightness levels where this happens.
I haven't looked at this recently, but I also remember noticing that
textures pixels seemed to be off slightly in brightness with respect to
the background. Are these just sypmtoms of how the background is drawn
in OpenGL?
Cheers,
Martin Spacek
PhD student, Swindale lab
Graduate Program in Neuroscience
Dept. of Ophthalmology and Visual Sciences
University of British Columbia, Vancouver, BC, Canada
+1-604-875-4555 ext. 66282
mspacek@xxxxxxxxxxxxxxx | http://swindale.ecc.ubc.ca
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