QHYCCD

QHY268C: Download speed of ASCOM vs. native driver

QHY268C: Download speed of ASCOM vs. native driver
« on: December 04, 2020, 06:05:24 AM »

This is about the different behaviors of the native vs. ASCOM drivers supplied by QHYCCD:


First, i have calculated the max frame rate for the QHY268C (APS-C, 16bit, 26.8MPixel) and get a max theoretical frame rate per sec(fps) on USB3 (max 5GBit/s) of: 6280 x 4210 pixels @16BPP = 423,020,800 (432MBit) of 12.7 fps.
The specified download rate from QHYCCD is 6FPS @16BIT, binning 1x1. So, that is perfectly fine.


I measured the download rates on my PC system with SharpCap (v3.2.6442.0, 32 bit).
When using the native QHY-driver, the frame rate shown in SharpCap was 5.9fps. this is confirmed by the timestamps of the 10 files downloaded and saved. All good so far.


However, when using the ASCOM driver provided by QHYCCD in the same setup and software, i measured a total download rate of 46sec [/size]for 10 images, i.e. 4.6sec per image. This is 27times SLOWER than with the native driver!! By the way, the download time in my standard Stro-Software (AstroArt7) with the QHYCCD-ASCOM driver is 15% faster (4.0sec).


This limits the possibilities to use this amazing camera significantly with other software, like AstroArt in my case.
Have others observed the same behavior? I have heard from users of other (astronomical or DSLR) CMOS cameras similar stories.
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I have done some measurements on image quality as well, but can not see or detect statistically a significant difference between images downloaded with the different drivers.


For classical DSO imagers like me, it would help saving on "unproductive" time (image selection, estimation of seeing, even focus, especially full frame focus).


Any thoughts on this?
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AstroBernd

Re: QHY268C: Download speed of ASCOM vs. native driver
« Reply #1 on: December 05, 2020, 12:03:49 PM »

I have looked a little deeper into the numbers delivered by the native vs. the ASCOM driver.
It looks to me like the native driver is only transferring even numbers, whereas the ASCOM driver seems to transfer both even and odd numbers.
Is this a correct observation?
Is the native driver leaving out halve the digitization?
Looking forward to some clarification.
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AstroBernd

Re: QHY268C: Download speed of ASCOM vs. native driver
« Reply #2 on: December 12, 2020, 09:27:45 AM »

Nobody having a comment on this? Really??


I have looked a little deeper into the numbers delivered by the native vs. the ASCOM driver.
It looks to me like the native driver is only transferring even numbers, whereas the ASCOM driver seems to transfer both even and odd numbers.
Is this a correct observation?
Is the native driver leaving out halve the digitization?
Looking forward to some clarification.
Clear Skies
AstroBernd

QiuHY

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Re: QHY268C: Download speed of ASCOM vs. native driver
« Reply #3 on: December 31, 2020, 11:29:50 AM »
Hello,

       Normally our SDK supply two mode. One is the live video mode which can get very fast frame rate. Like 6.8fps @16bit . The Sharpcap is using this mode.

       And there is another mode called single frame mode. In this mode. The camera will do more work than live video mode. So it will slow down the transfer speed.  The camera will clean a frame to avoid the RBI image remain. And then put the data to the DDR buffer. And then transfer from camera to the computer. So it will take more time.

      The time of the single frame mode also have relationship with the CPU. And also if it is USB3.0 port.  Sometimes if you use the USB2.0 port it will be slow also .


Best regards,
Qiu Hongyun
Qiu Hongyun

Re: QHY268C: Download speed of ASCOM vs. native driver
« Reply #4 on: January 07, 2021, 06:20:16 AM »
Dear Dr. Qiu,
Thanks for your reply.


1. Can you confirm that the "video live mode" is only using half the quantization (only even numbers, resulting in 15bit resolution)? I saw this when using SharpCap with the native driver (see my earlier post). Is this part of the reason for the high transfer speed of 6.8fps @16bit with software like SharpCap and native driver?


2. "Single frame mode" as you explain below sounds to be the better mode for Deep Sky imaging (with exposures of several minutes and full quantization). Would you agree to this?
What is the (maximum) download speed in 16bit, full frame in this mode under "optimal" conditions (USB3 port with original cable, fast CPU with fast SSD)? Can you confirm my measured values of about 4 to 5 seconds per frame with the ASCOM driver?


Those download speeds are still very fast compared to the cameras a few years ago! I just want to understand how close my setup is to the maximum theoretical speed for single frames.
 
Appreciate your reply
Thanks in advance
AstroBernd
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AstroBernd

Re: QHY268C: Download speed of ASCOM vs. native driver
« Reply #5 on: February 04, 2021, 09:58:46 AM »
Anything new to clarify the questions?
Thanks in advance

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AstroBernd