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Overexposing with autohisto set and other issues with Jupiter

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#1 skogpingvin

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Posted 19 October 2020 - 11:20 PM

Hi brains trust, I'm nearly entirely new to planetary imaging, being a wide-field narrowband nebula guy, but I have to do a bit of this for work (tough, huh?).

 

I've been teaching myself for six sessions now (two before I even pointed a scope to the sky), and I'm pretty happy with my progress so far, but it's time I began asking questions (although Tulloch from this forum has been very helpful - thanks Andrew!).

 

Hardware is a standard C8, 2x ED Barlow and QHY5III 462C. FireCapture cutout and planet sensing works well, got 35 FPS (sure I should be getting higher) saved as SER.

 

I've posted a screen shot of SER player in the middle of one of my output files, and it's clearly overexposed in green and red. This was despite having set autohisto to 69. I've also attached the settings from FireCapture at the bottom. Can anyone tell me what I'm doing wrong?

Overexposed SER frame.JPG

 

Subsequent to that, I added an IR cut filter, turned the autohisto down a little more and got a run of 10,000 frames that seemed OK. It was just over 5 minutes - is this too long for a single run on Jupiter?

 

I've posted a grab from SER reader for the run I eventually used. Is that too much noise? Too dark?

SER frame.JPG

 

I've just roughly processed the SER - I haven't learned much about that yet. Didn't use PIPP, used AutoStakkert to stack the best 90% of the 10,000, then sharpened (probably much too aggressively) and colour balanced using RegiStax.

jup_223507_lapl5_ap127_RS.jpg

 

Can people give me an idea of what the biggest weaknesses are, so I can work on these next?

 

Thanks, Bill

 

Attached File  Jup_221049.txt   868bytes   12 downloads


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#2 Tulloch

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Posted 20 October 2020 - 12:03 AM

Hi Bill, glad to see you got your post on the site smile.gif

 

The last image looks pretty good for a first(ish) attempt, although there are a couple of things to modify that I can see from your logfile.

 

Firstly, for the 462 sensor, set Wred = 69, Wblue = 86, Wgreen = 0 (ie no green offset). This should give you a good white balance straight out of the camera.

 

Turn HiSpeed = ON, you want to record the planets in 8 bit mode, it's faster, produces smaller files, and all you are capturing in the lower 4 bits is noise (although your ser viewer seems to indicate you are recording 8 bit - should check this anyway).

 

Try a faster shutter speed, I use 6.66ms to give me 150 fps, others go higher but I find 150 fps is a good balance between noise and frame numbers.

 

Try a faster USBTraffic value, too low and the maximum framerate is reduced, too high and it can crash the system. I find 80 works best for me.

 

Maximum video time for Jupiter = 3 minutes, Saturn and Mars can take 5 minutes without worrying about planetary rotation.

 

Only stack up to the best 50% of frames - 90% is way too high, you are including too many bad frames. Try a range, 10%, 25%, 33%, 50% (you can enter up to 4 numbers in AS!3) and see what effect that has.

 

The histogram looks pretty good, I usually aim for about 50% maximum, others go a little higher. I don't use the auto-histogram feature, I just set the gain manually at the start.

 

Other than those small things, you are looking pretty good smile.gif

 

Andrew


Edited by Tulloch, 20 October 2020 - 12:21 AM.

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#3 skogpingvin

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Posted 20 October 2020 - 12:39 AM

Thanks Andrew - I've changed my FireCapture settings to suit - pretty much - and I'll reprocess the 5 minute run using 3 minutes and a more picky quality criterion or two.

 

Bill



#4 Tulloch

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Posted 20 October 2020 - 01:14 AM

Firstly, for the 462 sensor, set Wred = 69, Wblue = 86, Wgreen = 0 (ie no green offset). This should give you a good white balance straight out of the camera.

Hi again, you might need to check those Wred, Wblue and Wgreen values, FireCapture seems to treat ASI cameras differently to QHY cameras. On ASI cameras Wred and Wblue are shown as values from 1 to 99 and Wgreen shown as an offset from 0, while for the QHY cameras they are shown as values from 1 - 127, with 64 as the middle value?

 

Therefore, the values for the QHY462C sensor should/could be:

Wred = 88

Wgreen = 64

Wblue = 110

 

Sorry for the confusion.

 

Andrew


Edited by Tulloch, 20 October 2020 - 01:15 AM.


#5 skogpingvin

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Posted 20 October 2020 - 02:54 PM

OK, thanks Andrew.

 

On other targets, I just muck about with these until the colour balance in the debayered preview screen is about right?

 

Bill



#6 Tulloch

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Posted 20 October 2020 - 03:30 PM

Ha! Don't get me started on methods of setting the colour balance on the different planets (but if you really have a few hours to kill, you can read about my adventures with colour accuracy in planetary imaging here lol.gif).

https://www.cloudyni...e-final-report/

 

If you don't have a few hours, then my advice would be to keep the same colour values for all planets, and (here is the controversial bit) don't do any colour balancing steps differently for any of the planets - after all, if the white balance is correct once, then why should it change? Others don't necessarily agree with this, you are of course free to do what you want, they are your images after all.

 

Looking at your low framerate for Jupiter again, another problem might be that your ROI on the display screen (which is different to the ROI of the Crop Box) is too large. There is only a certain amount of information that can go through the USB "pipe", and if you put too much through the pipe due to the viewscreen, then that means there is less that can go through as a recording. In short, reduce the height of the ROI to about double the target height (don't worry about the width) and watch your frame rate increase.

 

Also, if you are not doing this already, record the video in raw8 (undebayered) format. AS!3 is the best program for debayering the video stream, and recording in raw8 format means the videos are a third the size (since you are only record 1 set of information not 3) and frames rates will increase. There is a checkbox in the Firecapture options area that lets you observe the colour feed (which is essential for focusing etc) but will only record in raw8. See the checkbox below, it's in the "Settings/Image/Debayer" area.

 

Andrew

Attached Thumbnails

  • FC debayer capture settings.PNG


#7 TorstenEdelmann

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Posted 22 October 2020 - 12:07 AM

FireCapture seems to treat ASI cameras differently to QHY cameras. On ASI cameras Wred and Wblue are shown as values from 1 to 99 and Wgreen shown as an offset from 0, while for the QHY cameras they are shown as values from 1 - 127, with 64 as the middle value?

 

The reason here is that ASI cameras only support Wred and Wblue. Wgreen is added by FC and done inside the software by adding an offset from 0. The same applies to gain which is also not available for ASI cameras and also done inside FC.

 

Torsten


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#8 mikela

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Posted 12 December 2020 - 07:15 PM

What setting are you using for USB Traffic on the QHY5III462C?  I originally had mine set at 40 in Fire Capture.  The upper limit shows as 60 for me.  When I set it lower, it increased the fps.  I thought it was supposed to be the opposite of that?

 

Mike 


Edited by mikela, 12 December 2020 - 07:17 PM.


#9 happylimpet

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Posted 12 December 2020 - 08:47 PM

autohisto misbehaves with a colour camera. I think it was designed just for mono in which case it works perfectly  but when ive used it with my asi224mc ive had to use an unexpected value for autohisto...as i recall it had to be lower (which makes sense with your overexposure).


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#10 skogpingvin

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Posted 27 December 2020 - 05:14 AM

autohisto misbehaves with a colour camera. I think it was designed just for mono in which case it works perfectly  but when ive used it with my asi224mc ive had to use an unexpected value for autohisto...as i recall it had to be lower (which makes sense with your overexposure).

Yes, I think I'll go back to not using autohisto with the QHY5-III 462C. But it's a bit of a moot point, as the planet season is pretty much over now.

 

I'm looking forward to going back to our dark sky site in a couple of days time. It's been eight months and the Rosette awaits.



#11 JohnEEvans

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Posted 27 December 2020 - 08:14 AM

Others above have covered lots of capture tips. Just one from me on frame rate. I'm unfamiliar with your camera so there may be some limitations I'm unfamiliar with, but this is just a general point. You should be able to use pretty much all the available time to capture data, so if your exposure is 10ms you should be able to get to 100 fps, 5ms -> 200 fps, 2.5ms -> 400 fps, etc. If you are only getting 35fps then 2/3 of the capture time is being wasted.

 

The things that limit this will be bit depth, as above 8 is fine for planetary so set USB Traffic as high as you can without loosing frames (FC alerts on this). Then its down to how fast can your camera read and send data to FC. So my camera allows setting a ROI within the chip. On my camera this works by the chip reading a reduced sets of rows (note it always reads all columns so pointless limiting the ROI's columns). FC supports setting a ROI. You can see how this works by looking at the status in FC as you change the ROI. One of the pieces of data in the status is FPS, so as you set a smaller ROI you will see the theoretical FPS number increase.

 

Next, when you capture you will need to write the data read from the chip to disk. If you are limited by USB or PC disk write performance you can improve by using cutout. Note, cutout is different to ROI. ROI is setting an active region on the camera sensor, whilst cutout has nothing to do with this and is implemented entirely in FC. The advantage of using cutout is that you can crop down tightly on the planet whilst having a bigger ROI to keep the planet on the sensor as it moves around during capture. If you use cutout it will minimize the amount of data you save which helps the PC keep up with fast frame rates and will "significantly" speed up AS meaning you can skip preprocessing with PIPP.

 

The other thing I've had some issues with is memory in FC. You need to make sure you allocate enough to FC otherwise strange things will happen incl reduced frame rates. There is info on how to set this on the FC website (its in one of the videos). You can keep an eye on memory usage during capture, if it gets anywhere near 0 or the background changes from green to amber then you're in trouble.

 

There are plenty of tutorials on the internet about settings for AS and Registax. One thing I would say is that the settings are quite dataset dependent so what works bests for 1 person with one set of equipment on one capture won't be necessarily the best set of settings for the next person. So if you watch a Damian Peach video where he's sharpening an image of Jupiter he's got with a C14 with 5/5 seeing, 5/5 collimation and perfect focus and try those settings on your own data you might end up disappointed. So you have to play around. What I tend to do is pick a setting, say AP size in AS. Process several images in exactly the same way except for changing the one variable under scrutiny and produce a number of output files. Load them into an image processing piece of software, like Photoshop (I use Gimp) as separate layers. Align the layers if necessary and then flip between the images. This is a good way of seeing small changes.

 

It is useful to watch some processing videos though. The planetary processing software tools are essentially undocumented so not so easy for newcomers to get familiar with.

 

Your Jupiter is pretty good, so good luck!




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