Re: [Elphel-support] Flash on a two camera system
Andreas, Why do you need pulse _before_ trigger? With this senor exposure of the first line start 8 scan lines after the trigger, last line exposure starts 1/15 sec later. So if you want to use a flash, you need to set the exposure time 1/15 sec and trigger flash 1/15 after the trigger. The FPGA has delay timer, when the camera is triggered externally, this programmable delay is between the arrival of the sync pulse and the sensor triggering. When the camera is set to trigger directly from the FPGA (trigger condition =0), the delay sensor is triggered immediately, and the output sync is delayed by the programmed value - you may use it for the flash. Unfortunately it is for a single camera only. If you still need pulse before the sensor trigger - you may just reverse the trigger source - use external pulse, apply it to multiple cameras in parallel - each camera can be individually delayed by programming TRIG_DELAY parameter. Andrey ___ Support-list mailing list Support-list@support.elphel.com http://support.elphel.com/mailman/listinfo/support-list_support.elphel.com
Re: [Elphel-support] Flash on a two camera system
Andrey, In fact we develop a led light and not a discharge flash, therefore the light isn't deposited in a short period. You say the exposure of the last scanline starts 67ms after the first line. I'm trying the get light intensity high enough for an exposure time of 5ms. This means that the leds have to be turned on for 72ms ? And additionally I don't know how long they need to reach the full intensity, that's why I asked if its possible to get the signal before the trigger. How would you connect the led driver circuit to the cam? Does it matter that the signal is only for one cam? They are closely mounted together, so the signal can be used for both, can't it? Have consumer digital cameras also the delay between the exposure of the first and last line? Does that mean that during a fast movement the first and the last line in the picture differ significantly? Andreas Andrey Filippov schrieb: Andreas, Why do you need pulse _before_ trigger? With this senor exposure of the first line start 8 scan lines after the trigger, last line exposure starts 1/15 sec later. So if you want to use a flash, you need to set the exposure time 1/15 sec and trigger flash 1/15 after the trigger. The FPGA has delay timer, when the camera is triggered externally, this programmable delay is between the arrival of the sync pulse and the sensor triggering. When the camera is set to trigger directly from the FPGA (trigger condition =0), the delay sensor is triggered immediately, and the output sync is delayed by the programmed value - you may use it for the flash. Unfortunately it is for a single camera only. If you still need pulse before the sensor trigger - you may just reverse the trigger source - use external pulse, apply it to multiple cameras in parallel - each camera can be individually delayed by programming TRIG_DELAY parameter. Andrey attachment: office.vcf___ Support-list mailing list Support-list@support.elphel.com http://support.elphel.com/mailman/listinfo/support-list_support.elphel.com
Re: [Elphel-support] Flash on a two camera system
On Wed, Apr 13, 2011 at 21:03, Andreas Bean off...@beanbox.com wrote: Andrey, In fact we develop a led light and not a discharge flash, therefore the light isn't deposited in a short period. You say the exposure of the last scanline starts 67ms after the first line. I'm trying the get light intensity high enough for an exposure time of 5ms. This means that the leds have to be turned on for 72ms ? And additionally I don't know how long they need to reach the full intensity, that's why I asked if its possible to get the signal before the trigger. How would you connect the led driver circuit to the cam? Does it matter that the signal is only for one cam? They are closely mounted together, so the signal can be used for both, can't it? Have consumer digital cameras also the delay between the exposure of the first and last line? Does that mean that during a fast movement the first and the last line in the picture differ significantly? ERS (Electronic Rolling Shutter) has been used in all consumer as well as professional CMOS based camera systems to date. Regards Sebastian Andreas Andrey Filippov schrieb: Andreas, Why do you need pulse _before_ trigger? With this senor exposure of the first line start 8 scan lines after the trigger, last line exposure starts 1/15 sec later. So if you want to use a flash, you need to set the exposure time 1/15 sec and trigger flash 1/15 after the trigger. The FPGA has delay timer, when the camera is triggered externally, this programmable delay is between the arrival of the sync pulse and the sensor triggering. When the camera is set to trigger directly from the FPGA (trigger condition =0), the delay sensor is triggered immediately, and the output sync is delayed by the programmed value - you may use it for the flash. Unfortunately it is for a single camera only. If you still need pulse before the sensor trigger - you may just reverse the trigger source - use external pulse, apply it to multiple cameras in parallel - each camera can be individually delayed by programming TRIG_DELAY parameter. Andrey ___ Support-list mailing list Support-list@support.elphel.com http://support.elphel.com/mailman/listinfo/support-list_support.elphel.com ___ Support-list mailing list Support-list@support.elphel.com http://support.elphel.com/mailman/listinfo/support-list_support.elphel.com
[Elphel-support] Flash on a two camera system
Andreas, that depends on what are you trying to capture. If ERS distortion is not a problem in your case, and the LED is just to provide more light, not limit the exposure - yes, you can do that (same as if LEDs were always ON for the camera). If on the other hand, you need LED as a snapshot shutter than you have to reduce ambient light or increase the LED brightness and simultaneously add neutral filters to the camera lens. Andrey On Wed, Apr 13, 2011 at 1:32 PM, Andreas Bean off...@beanbox.com wrote: Andrey, I can't set the exposure time even near 67ms. We have difficult lighting conditions. For example, we have an indoor room with a bright window where the cam is moving. Setting the exposure time to 72ms will give me a blurred image of the window. Anything else may be sharp due to the fact that it is only lighted for 5ms. Is the only option to set the exposure time to 5ms and turn the leds on for 72ms? Andreas Andrey Filippov schrieb: Sebastian, Most consumer cameras with ERS have additional mechanical shutter - it opens 1/15 sec (if they used the same senor) after the sensor starts exposing the first line, readout starts after the shutter closes. When using the bright LED it the LED on state is virtually the same as mechanical shutter open Andrey ERS (Electronic Rolling Shutter) has been used in all consumer as well as professional CMOS based camera systems to date. ___ Support-list mailing list Support-list@support.elphel.com http://support.elphel.com/mailman/listinfo/support-list_support.elphel.com ___ Support-list mailing list Support-list@support.elphel.com http://support.elphel.com/mailman/listinfo/support-list_support.elphel.com
Re: [Elphel-support] Questions regarding zoom in ... now enhance blog post
On Tue, Apr 12, 2011 at 7:28 AM, Florent Thiery florent.thi...@ubicast.euwrote: Hello, First, please let me introduce our use case; we are trying to use Elphel cameras (353 + Computar 4-8mm 1/2) to get maximum resolution ( FullHD), 25 fps video. Our current problems are about image quality when zooming on details (blurred images); in other terms, we are trying to improve the rendering quality as much as possible to have cleaner images. In this context, last year we implemented http://code.google.com/p/gst-plugins-elphel/ but only changing the debayering algorithm did not improve the quality enough for our application (at least not when compared to the processing overhead). I was wondering about the method described in the awesome article Zoom in ... now enhance: - are there any specifics about the method being for Eyesis only (my guess is it's not) ? Florent, sure it can be used with as single camera too. But it may be too slow for processing videos - it now takes 2-3 minutes/frame on an i7 with 8 GB of RAM (in multi-threaded mode) - regarding the calibration, what are the invariable factors ? Is the calibration required for: - every camera model/generation (depending on camera/sensor manufacturing design/process variations) ? - every lens model (depending on lens model) ? - every lens tuning (zoom level / focus / iris ...) ? - climatic condition changes (temperature, ...) ? This was designed for fixed everything (though we did not notice degradation with changing temperatures). But there is a significant difference between lenses even the same model. The lenses we used do not have zoom, and iris does not make much sens for such lenses - with 2.2 um pixels you can not close lens more than ~4-5.6 because of the diffraction, small sensors do not provide much control over DoF and using iris to limit light - not really needed with ERS sensors - they can handle very short exposures perfectly. And of course, focus setting would influence results too, as well as the lens orientation. - the hidden question behind this is: how can this technique be used in production ? Working with wide angle lenses ( 45x60 degrees FOV) we do not have enough room to capture the test pattern in a single shot, so software is able to combine multiple shots where the test pattern covers just a fraction of frame. We did not work on optimizing computational time of the calibration, so it takes several hours to process data ftom 8 camera modules. Current calibration is only designed for the aberrations correction, but I'm now working on the precise distortions calibration (with some 1/10 pixel precision), we plan to use it for panorama stitching, it can also be used for making measurements with the camera. This calibration will use the same pattern we use fro aberration correction, just at closer range, so the pattern will cover the whole FOV (minor out of focus is not a problem here). - For a given camera/lens combination, could a public database of tuning data reduce the calibration requirement (in a similar fashion to A-GPSes which download correction data from the network to increase performance on low-quality reception and/or chips http://en.wikipedia.org/wiki/Assisted_GPS) ? Our goal was to have precise individual lens correction, we did not experiment with correction of the lens model - it probably is possible, but with less correction, of course. Software has multiple tuning parameters, it should be possible to do that. - is there a hope of having such a feature (in the long term) integrated in the camera itself (i.e. grabbing an mjpeg stream who had the corrections made right before the encoding) ? Not in the near future, at least. We now heavily rely on post-processing, camera role is just to capture all what sensor can provide, in as much raw form, as possible. Andrey Thanks Florent ___ Support-list mailing list Support-list@support.elphel.com http://support.elphel.com/mailman/listinfo/support-list_support.elphel.com ___ Support-list mailing list Support-list@support.elphel.com http://support.elphel.com/mailman/listinfo/support-list_support.elphel.com
