Path: utzoo!mnetor!uunet!husc6!bbn!rochester!udel!princeton!mind!dan From: dan@mind.UUCP (Dan Kimberg) Newsgroups: comp.sys.amiga.tech Subject: Re: An Infinite Number of Colors Message-ID: <2401@mind.UUCP> Date: 29 Apr 88 04:44:11 GMT References: <2388@mind.UUCP> <3707@cbmvax.UUCP> Reply-To: dan@mind.princeton.edu (Dan Kimberg) Organization: Cognitive Science, Princeton University Lines: 56 I'm posting my response in hope of someone seeing this and getting a sudden inspiration along the lines of a solution to my problem. Also because I didn't explain very well what I'm doing and why I'm doing it. The experiments I want to perform have to do with binocular vision, specifically stereopsis at isoluminance. Anyone who has every looked through an old "stereopticon" at two pictures, nearly identical but taken from a few inches apart, should have a good idea what stereopsis is - it's the depth effect you get from the disparity between what your eyes see. In order to test this, I wanted to generate isoluminant random dot stereograms on the amiga - stereo pictures which are just bunches of dots until you look at them in stereo. I did, and got the results I hoped for, but there's a strong feeling that it's a poor test if I was at anything short of isoluminance. Oh, isoluminance means the dots are of uniform luminance, i.e. distinguishable only by color contrast information. So the problem is I need to be able to generate these stereograms with individually distinguishable dots of two different colors, such that at least one (ideally both) of the colors can be varied continuously. It doesn't much matter what the levels are, so long as I can show that for the subject there is no point along the continuum at which they are unable to resolve the disparity. More specific responses: In article <3707@cbmvax.UUCP> hedley@cbmvax.UUCP (Hedley Davis) writes: >of charecters ) look pretty bad. Pots would also tend to not be >very repeatable, and therefore might not be suitable for serious >experimentation. Repeatability isn't a big problem as long as I can get them to be monotonic - i.e. always get brighter when i turn them one way, darker the other. Fuzziness would be bad, though. I think the display is already fuzzy enough. >Seems to me that video-dac manufacturers make D-A converters with very >nice little 75 ohm outputs built right in. You could work out a scheme >where you connect the four bits from the RED gun to the higher 4 bits >on a videodac, and the four bits from the green gun to the lower four >bits. This would give you a 75 ohm 256 step output. You could then >switch this output to the R,G or B input on the monitor and presto, >lotsa shades of R,G, or B. Hmm. That's actually a nice suggestion. Although I need to have at least two colors, I could leave the third color connected normally, right? Ideally I'd like to be able to use all three colors that way, though. >Another technique would be to use dithered patterns to simulate various >brightnesses. This would require the subject under test be sufficiently >far from the monitor that the overall color is visiable, but not the >underlying patterns. Unfortunately subjects will be about ten inches away. >Whatcha doin anyway ? >Hedley Hope I walked the middle ground between concise and explanatory up there. Thanks a lot for the help. I really have no feel for how the hardware behaves, so I can use all the help I can get. I think I still want to find something which will give me full control from a black box, though if it's at all possible. Thanks again, -Dan (dan@mind.princeton.edu)