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Download speed on ASCOM vs. native drivers

Posted: 07 Nov 2020, 17:08
by AstroBernd
I noticed that the download speed of images is much slower in ASCOM vs. native drivers in my new QHYCCD CMOS camera (QHY268C). When i use Sharpcap, i see 5.6 images/ second (fps) downloaded and stored as FITS files without any dropped frames. So, the whole setup (camera, driver, USB3, Software, hardware) is capable of doing that. When i use the ASCOM driver provided by the Camera manufacturer, the download time is getting much longer, i.e. 4 seconds per frame (a whopping factor of 20!). This means this is related to the ASCOM driver architecture and how it passes on the data to the receiving software (here: Sharpcap). I observed similar download times with AstroArt 7, so, no extra delays :-).
* Is this an observation others can share as well?
* Any plans to get the native drivers for ZWO or QHYCCD cameras directly interfaced into AstroArt? (Sorry, i am not a Software expert, so this question may be not exactly correct, but i hope you can see what i mean): Faster download times also in AstroArt!
Just a thought
Bernd

Re: Download speed on ASCOM vs. native drivers

Posted: 08 Nov 2020, 09:08
by Rudi
That’s true, data download via ASCOM is significantly slower than through native drivers, at least for Canon and ZWO, which is the only cameras I’ve been using.
For deep sky photography, it doesn’t really matter for me, if every two minute exposure takes one second or 1/20 second to download.
But when focusing with AstroArt, both manual and automatic Full Frame Auto Focus, it would speed things up considerably,if AstroArt used native camer drivers.
I don’t know how easy ZWO’s SDK is to use, that’s up to Fabio to decide.

Re: Download speed on ASCOM vs. native drivers

Posted: 08 Nov 2020, 09:47
by AstroBernd
I fully agree, Rudi, no big deal for deep sky images, but a lot of possible “unproductive “ time saving.

Re: Download speed on ASCOM vs. native drivers

Posted: 08 Nov 2020, 12:29
by fabdev
Interesting: first, is the quality really the same? Downloading a multimegapixel image in 0.2 seconds could mean that readout mode was different (more quantization, faster ADC setting, lossy compression?). The following test could tell: a 5-10 seconds flatfield-like image at half range (30000 ADU), downloaded in both modes, then compare the standard variation and the quantization of both images.
Second question: if the two images are really the same, why the ASCOM driver is slower? COM is able to transmit megabytes of data really fast, all the operations are done in memory.

Re: Download speed on ASCOM vs. native drivers

Posted: 08 Nov 2020, 15:41
by Rudi
Perhaps it’s because the live view in ZWO’s software is lower quality, I don’t know.
The focus liveview probably also uses ROI.

Re: Download speed on ASCOM vs. native drivers

Posted: 08 Nov 2020, 19:26
by Rudi
I found an old post on the Danish forum astronet here:
https://www.astronet.dk/forum/viewtopic.php?t=2460

Here I wrote a little about the download speed.
To put it short, my ZWO 1600MM with 4,656 x 3,520 pixels at 16 BPP = 262,225,920 Bit should be able to transfer ca 20 FPS over USB 3. However, the real number is ca 14 FPS.
I have measured 10-12 FPS with FireCaputre, when using a dedicated USB 3 cable to the camera.