Timing of the dither commands

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RudyOtten
Posts: 16
Joined: Fri Feb 08, 2019 6:50 pm

Timing of the dither commands

#1

Post by RudyOtten »

Good day Robin,

I'm using version V4.0.7572 (64bit) of SharpCap.
I noticed the following:
When you use a exposure time of 60S and you save the live-stack each 3 minutes (180S) and you
ask for a dither each 120S, then there will be no dithering happening at all.

When you look at the 3 screenshots you see that the dither counter nicely starts at 120 but after the
first exposure (60S) the timer now shows that the dither will happen after 72.1 seconds and when the next
exposure has finished (so total integration time is 120S) the message will show that next dither is schedules at 9.8S.
But then the 3 frame is captured and the stack is saved and all will start from point zero again.
No dithering happening at all.

As if the dither timers are not synchronized with the frame timers???

I'm sure you can fix this ;)

Regards,

Rudy

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admin
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Re: Timing of the dither commands

#2

Post by admin »

Hi,

I think that is how it is supposed to happen...

The dither interval specified is a minimum value - SharpCap will dither at the next frame finish after the interval has expired. So, if you have 90s set as the dither interval and the frames are 60s then you would expect it to dither after the 2nd frame (and every 2nd frame after that).

The dithering code is reset when the stack is reset, so the time delay begins afresh each time the stack is reset. Is this the optimum strategy? Not entirely sure. I like the idea of each stack starting 'clean' with no influence from the previous one though.

What you are running up against is that this is designed around taking 10s of frames in each stack rather than just a handful. If you set the reset time to 30 minutes with 60s frames then all of the above becomes largely irrelevant - with your dither interval of (say) 90s then you will get 15 or do dither operations happening during the stacking period and it's not critical for them to occur at an exectly planned point, just so long as they happen every 2 frames or so.

I suppose the question is ... are you really wanting to run a stack of 3 frames with a single dither somewhere in it, or was that just for testing purposes?

cheers,

Robin
RudyOtten
Posts: 16
Joined: Fri Feb 08, 2019 6:50 pm

Re: Timing of the dither commands

#3

Post by RudyOtten »

Hi Robin,

Thanks for the answer, I'm not trying to find bugs by using the system in an awkward way, it was just that it is strange
that after the first frame of 60S the dither counter did not go down by 60S but with some other number. That is all.
And I do use it like this a lot, for me I want to save the stack after about 5 minutes, just because you don't want the end result be
spoiled by an satellite or airplane, after saving these in between stacks I use PI to integrate it into a final stack.
What I do lately is using a value for the dither that is not a multiple of the exposure time. So that is a kind of a workaround :D .

Have you seen my answer on topic "viewtopic.php?p=19888#p19888"

Enjoy Eastern,

Rudy
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Re: Timing of the dither commands

#4

Post by admin »

Hi Rudy,

have you considered using the 'sigma clipping' stacking option? After the first few frames (which establish the 'expected' variation of pixel brightnesses), it should reject satellite/plane trails from being added to the stack - basically it sees the pixel value in the trail is so different from the normal value in a particular position of the image that it will ignore it.

I think I replied to your latest post in the other thread.

cheers,

Robin
RudyOtten
Posts: 16
Joined: Fri Feb 08, 2019 6:50 pm

Re: Timing of the dither commands

#5

Post by RudyOtten »

Thanks Robin,

I will give that a try next time, it's the same as PI's sigma integration routine.
As for the last comment on the topic related to the 32bits saving.
I added a comment after you had posted an explanation.
In the 32bit version there seems to be an offset of 0.5 in the resulting file.
And that is not the case in the 16bit version.
With 0.5 I mean that the black is showing as gray. (3FFFFFF)

Rudy
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Re: Timing of the dither commands

#6

Post by admin »

Hi Rudy,

I think I replied to your comment on 0.5 offset - it's on the next page of that thread ;)

cheers,

Robin
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