Timeline for Raspberry Pi stereo camera frame synchronization/genlock (video or still image)
Current License: CC BY-SA 3.0
15 events
| when toggle format | what | by | license | comment | |
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| Aug 21, 2014 at 10:35 | comment | added | Kozuch | It probably wont be that bad with a latency of a default Raspbian kernel: emlid.com/raspberry-pi-real-time-kernel-available-for-download I guess this may be considered a soft real-time and suit my needs more then enough (considering 1ms precision)? The average values are almost the same. | |
| Aug 13, 2014 at 21:51 | comment | added | Connor Wolf | Really, running a RTOS doesn't mean it'll cost anything more, you could theoretically even just do it right on the rPi (run bare-metal). The issue is mostly lack of documentation. | |
| Aug 13, 2014 at 21:51 | comment | added | Connor Wolf | @Kozuch - If you're shooting for 10 ms, rather then 1 ms, that's a lot more tractable, I think. Really, it'll /probably/ work, I just want to be sure you're aware of the possible complications down the road, particularly if later on you decide to start adding other tasks to the running rPi. | |
| Aug 13, 2014 at 8:02 | comment | added | Kozuch | @ConnorWolf: The image/video capture will be the only task on my Pi setup and there will be no other load. Units will be disconnected from all COMs (ethernet etc.) However, I must agree with you on a theoretical level with RTOS. But RTOS with stereo camera is totally different price level, right? The question is how much of the RTOS capability will a clean Raspbian install be able to deliver. Simply if I get sync within few ms (say under 10ms) this is still great result for me in this price range. | |
| Aug 13, 2014 at 1:38 | comment | added | Connor Wolf | @Kozuch - I don't think so, though it would probably be a bit better. The issue is the delta between when you want to take the image, and when the hardware actually takes the image. If linux is servicing another thread, you have to wait for the next context-switch to actually have your thread do anything. | |
| Aug 12, 2014 at 14:16 | comment | added | Kozuch | @ConnorWolf: Would my option #2 (using Compute Module with 2 cameras on it) eliminate possible issues with trigger latency since it would employ a SW trigger that might actually be more low-level than GPIO trigger? | |
| Aug 12, 2014 at 11:20 | comment | added | Connor Wolf | @Kozuch - The issue is that the trigger latency may not be determinisic, because linux may be doing something else in the background. Linux is not a realtime operating system. You may get away with what you want, but any realtime behaviour is going to be fairly brittle, and likely to be broken if you load the system at all. | |
| Aug 12, 2014 at 10:05 | comment | added | Kozuch | @RJR: I dont mind a delay between the trigger and photo being taken, given it will be exactly the same for both Pi units. Of course a long delay wouldnt be nice but again my main goal is frame synchronization. I guess both units should behave exactly the same in case I do a 100% same install and setup? | |
| Aug 12, 2014 at 9:45 | history | edited | Kamil | CC BY-SA 3.0 |
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| Aug 12, 2014 at 9:44 | comment | added | Kamil | @RJR I haven't tested Pi camera response time, I don't have one. I was using cheap USB Logitech camera for my CV project. | |
| Aug 12, 2014 at 9:43 | comment | added | Kamil | @Kozuch I think Compute Module Kit is cheapest device with two CSI interfaces. | |
| Aug 12, 2014 at 3:28 | comment | added | RJR | Have you checked the time it takes for the PI camera module to take a picture, and how much deviation there is in that time? I think you might struggle with ms-level accuracy, not because of the triggering mechanism through GPIO, but the delays between the trigger and the photo being taken. Also, on a cloudy day, a 10ms shutter speed (1/100) isn't unheard of. | |
| Aug 12, 2014 at 0:09 | comment | added | Kozuch | Thanks a lot for your answer! I do not plan any CV processing on the Pi. I only need to record the video in frame sync and I will do all other work on PC. Dont you know if there may be another board on the market that may have 2 CSI interfaces (or other camera interfaces but not USB camera) and is cheaper than Compute Module Kit and could do the same job? | |
| Aug 12, 2014 at 0:05 | history | edited | Kamil | CC BY-SA 3.0 |
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| Aug 11, 2014 at 23:57 | history | answered | Kamil | CC BY-SA 3.0 |