Dropped frames in ROI at high fps

[Pulsar59]

System : windows 11
camera : Player One Uranus-M (SDK charged in SC folder) in USB3
Nothing else plugged in on the computer

I use Sol'Ex (Spectroheliograph) for which I have to set an ROI of 2800x120 (8 bits) and exposure time 2,34 ms, giving 417 fps.
Remark : camera is not at max, can reach 540 fps at this ROI.

As soon as previewing starts, (even not recording), dropped frames occur (see log).
This problem starts occuring for exposures < 4 ms.
No effect of USB speed tuning. No effect of memory settings.
If I remove the ROI, with the camera at its max speed (45 fps) : no dropped frames.

I have also the same problem with a ZWO ASI178 mono. But this camera is recognized in SC3.2 and with this old SC version there is no problem at all !

This is extremely annoying since it results in missing slices in the reconstructed Sun image, therefore not usable.

Thanks for any idea...

Olivier.

[Pulsar59]

Update :

there seems to be an improvement with the very latest version (4.1.13295) with no more dropped frames in the conditions I mentioned above (2800x120, 8 bits, 2,34 fps, therefore 417 fps).
I saw in the release notes for one of the latest varsions "Improvements for performance with high frame rates", which I suppose improved the situation.
I still have to make more tests to be sure the problem is solved, I will report here.

[admin]

Hi,

glad to hear that the update seems to have helped - the version you were using was quite old in SharpCap terms (from December last year), so there have been quite a lot of bug fixes and improvements since then.

cheers,

Robin

[Pulsar59]

Thanks,

with a more extensive test (in reeal conditions but with no Sun since it's cloudy) I see 1 or 2 dropped frames for about 10 from 21 SER I recorded on SSD. For example :

Debug 15:15:16.756732 #1 Notification (Status=OK): Capture Stopped - Captured : 7203 frames (2 dropped) in 0:00:17,4 at 414.3 fps -> D:\Sun\2025-05-07\Capture\15_14_58.ser

This is much better than before (where I had 6-10 dropped frames at each SER) but not perfect.

I need a Sun to see if this is visible on reconstructed images. I hope no.

It is certainly not related to hardware sine Firecapture never shows dropped frames with the same setup. But I prefer SC for Sol'Ex imaging !

regards,

Olivier.

[admin]

Hi Olivier,

it's probably not worrying about a small number of dropped frames like that, and the comparison between SharpCap and FireCapture isn't particularly helpful to be honest, since we don't know any details about how FireCapture counts dropped frames.

In this case, SharpCap isn't reporting dropped frames at the camera side, but rather cases where frames that have arrived at SharpCap don't make it through to display/capture for some reason - this can be that perhaps something isn't ready at the time the frame arrives, or that a frame arrives at the point it needs to be saved when the capture file is already being closed down. If you are getting regular increments to the count then it usually means that *something* in the software is failing to keep up with the flow of images, but a handful happening at the start/end of capture or when activating certain features is not unusual.

cheers,

Robin

[Pulsar59]

hello Robin,

"something isn't ready at the time the frame arrives" that's probably the case, from what I observe.

What is strange is that the old SC3.2 does not show this issue (but does not recognize new cameras, of course). Something must have been changed in SC4 that causes this behaviour at high fps. But it seems to be solved now.

[Pulsar59]

hello,

Today I saw something that may help.

I acquire 21 SER of the Sun using a script that laso moves the mount in AD (back and forth)
The reconstructed image from the first SER has always missing frames (ruins the image). This is because, although the dropped frame counter always shows 0, I can see the fps counter slowing from 405 fps to 395 or so during a fraction of second. This indicates missing frames.

If, at the end of the first SER, I slightly touch the USB Speed slider (either up or down, does not matter) all the 20 following SER are fine without missing frames !
This is rather weird but it works.
Hope that helps,

Olivier.

[admin]

Hi Olivier,

well, that is a weird one - I did notice while investigating this that I have never wired up the Player One support in SharpCap to properly check the lost frame count from the SDK, so I will add that at the next update, which might help reveal those lost frames that you are seeing during the speed drops. Not sure that it will help in any other way though.

cheers,

Robin

[Pulsar59]

Thanks Robin,

I will check that on update and report here.

regards,

Olivier.

[admin]

Hi Olivier,

I had a look at how the code was working for the PlayerOne cameras and found a minor issue that could cause dropped frames as the frame rate approached/passed 500fps - sometimes SharpCap would wait too long to collect one frame, meaning that the next was ready almost instantly and that irregularity in the rate was causing problems. I have a fix for that now, so that should help in the next update.

cheers,

Robin