From: michael.balda@gmail.com   
      
   Am Donnerstag, 6. Februar 2014 05:21:44 UTC+1 schrieb haitic...@gmail.com:   
   > On Wednesday, February 5, 2014 8:03:37 AM UTC-5, Michael Balda wrote:   
   >    
   > > Am Samstag, 1. Februar 2014 09:50:46 UTC+1 schrieb haitic...@gmail.com:   
   >    
   > >    
   >    
   > > > On Friday, January 31, 2014 6:18:23 AM UTC-5, Michael Balda wrote:   
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > > > I'd like to use a pattern projector for computer vision tasks. The   
   pattern can be in the NIR range, should not repeat itself but doesn't need to   
   be described exactly, so random noise, speckle etc. should be fine. It would   
   be preferrable, if the    
   pattern can be restricted to a defined field of view instead of being   
   omni-directional and was stable over time. Of course there are several   
   different approaches but I would like to find one which is    
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > > >    
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > > > (a) cheap,    
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > > >    
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > > > (b) robust,    
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > > >    
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > > > (c) efficient (in terms of power consumption),    
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > > >    
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > > > (d) not too complex,   
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > > >    
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > > > (e) has good availability of components and    
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > > >    
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > > > (f) is monochromatic or has small bandwidth.   
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > > >    
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > > >    
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > > >    
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > > > Thanks in advance for any suggestions.   
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > > There's random and then there's random. Ditto for monochromatic. It   
   would suit the discussion if you could say more about what you are using it   
   for. I like the multiple led or laser diode solution best because it has no   
   moving parts. In this    
   approach, the Picaxe, a $5 chip, outputs PWM (Pulse Width Modulation) pulse   
   train to say 5 led's separately. This runs in the background on the Pic. Very   
   easy to do. The randomness is combinatorial in nature, so even if you have   
   each led glued to a    
   ground glass scattering screen, and even if each pattern is fixed, the   
   combinations are very random, as the random number generator on the chip sets   
   each led differently.    
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > > I believe there is a "rand" function on board, but I am in habit of   
   running a few times to prime pump, then filling an array with the "random"   
   numbers, and then using subsequent random numbers to index into the array.    
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > > Perhaps this is a "thought experiment" on your part. Anyway, fun to   
   think about.   
   >    
   > >    
   >    
   > > >    
   >    
   > >    
   >    
   > > > jb   
   >    
   > >    
   >    
   > >    
   >    
   > >    
   >    
   > > Thanks for the suggestions. The purpose is to generate an intensity   
   inhomogeneity in camera images even on homogeneous surfaces. This can be very   
   useful for finding  correspondences in stereo-vision. Repetitions can yield   
   false correspondences, so    
   that's why the pattern should be pseudo-random. Since high contrast even in   
   daylight would be nice, small bandwith and efficiency are an issue.   
   >    
   >    
   >    
   > Should it be continuous or intermittent? Sounds like you need bright light   
   source. Portable?   
      
   Of course it would be optimal to synchronize the illumination with the   
   integration process of the camera sensor, which basically means for each   
   frame: flash for some micro-seconds and remain dark while the sensor is read   
   out. But for a first approach,    
   continuous could also be okay.   
   A portable solution would be great, at least for indoor usage where you don't   
   have to deal with bright, direct sunlight.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)