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Firecapture bit- and file settings

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#1 SupernovaDust

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Posted 05 July 2020 - 01:59 PM

Hello,

 

I am pretty new to planetary imaging and have a hard time understanding what my camera is recording, what it should be recording and why. My weapon of choice is the ASI290mc mounted on a NexStar 6" Evo and my target is Jupiter. I record on a 4-core laptop with USB3 and SSD, hitting 100fps worked even before the beta most of the time and I always set the ROI to just fit the object I'm recording. I know (I think) that I should always record without debayering, with as high a framerate and low gain as possible to get over 50% histogram, debayer later in AutoStakkert.

 

The camera can record in 12bit but all my footage is recorded with 8bits according to SER-player. 8bit gives me only 256 colors while 12bit would give me 4096. But FireCapture has only either 8 or 16 bits and although my cam can only record in 12bit, the SER-player says it's 16bit if I chose this setting in FireCapture. Now I know from forum posts here that the software always writes 16bit into the SER-header regardless of the cameras abilities but how do I know what my camera really recorded?

 

Also, when I switch to 16bit mode in FireCapture, the 3-colored histogram turns into a single-color wave but SER-player still says that its 16bit RGGB. This leaves me with the following questions:

 

- For Jupiter, Saturn and Moon, should I record in 8bit or 16bit and why?

- Do I lose color information when recording in 16bit as indicated by the mono-color histogram or can the information still be debayered afterwards in Autostakkert?

- If I don't lose color information, how can I balance the histogram in 16bit? In 8bit I need to dial down the green channel to have all 3 colors on roughly the same level. If I don't adjust it, my pictures have a green tint.

- Is SER the best format to record footage or should I opt for TIFF/FIT/BMP pictures, what works better with AutoStakkert?

 

Hope someone can clarify this because after spending half the sunday on google I still couldn't figure out which recording settings to use for my cam.

 

Clear skies!

raphael



#2 Tom Glenn

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Posted 05 July 2020 - 03:35 PM

The short and oversimplified answer to your question about bit depth is, don't record anything above 8 bits.  There can be exceptions, but these don't apply to anyone asking these questions.  And of course, this only applies to planetary (and most lunar) imaging, but not deep sky imaging.  

 

Anything above 8 bits has to be saved in a 16 bit file format, whether the original capture was 10, 12, 14 or 16 bits.  If you select the "16 bit" option in Firecapture, and don't enable "High Speed", then the program will record whatever the highest bit depth is for your camera.  Nobody really knows how "High Speed" works, but the ZWO cameras will reduce the bit depth, usually from 12 to 10 bits.  However, the point is somewhat moot when recording in 8 bits anyway, yet enabling High Speed does often increase frame rate, without any negative effects.  

 

8 bits only records 256 tonal values versus 4096 values for 12 bits.  The reason it doesn't help is that if you look at the tonal value for any individual pixel of the image in the live view, you will almost always notice a fluctuation of at least 1 tonal value (out of 256) due to atmospheric turbulence (typically much more than 1 value).  The atmosphere introduces a type of noise, which is reflected in uncertainty in the measurement.  A change of even 1 value, say from a level of 80 to 81 (again, out of 256), would already completely consume the extra 4 bits of information.  So the extra precision of the 12 bit recording would be worthless, because it would just be recording the atmospheric noise.  In these cases, a stack of 8 bit images yields equivalent precision to a stack of 12 bit images.  Indeed, the final stack does have more than 8 bits of information, which is one of the great benefits to stacking.  If you had minimal atmospheric turbulence, you could benefit from a 12 bit recording, but almost nobody encounters these conditions.  The requisite conditions to benefit from recording above 8 bits are far better than what most people would report as "very good" seeing.  And 12 bit capture mode doubles your file size and often cuts your frame rate in half. Not a good thing for planetary imaging.  

 

I'll let others address your other questions.  Ser is fine, although most people record AVI for planets.  Color tints can be caused by a variety of factors, and you can balance the colors in processing.  


Edited by Tom Glenn, 05 July 2020 - 03:50 PM.

  • FlorinAndrei, roelb and SupernovaDust like this

#3 SupernovaDust

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Posted 06 July 2020 - 03:37 AM

Hello Tom,

 

thank you for the reply, this explains it perfectly wink.gif I figured that "more is always better" but obviously not if it means more noise.

 

I had to test it myself with the recent beta of FireCapture and although I had Highspeed on, the footage was captured in 12bit at 99FPS according to the log (4GB ram buffer helps alot):

File type=SER
Binning=1x1
Bit depth=12bit
Debayer=no
ROI=400x414
ROI(Offset)=904x256
FPS (avg.)=99
Shutter=10.00ms
Gain=270 (45%)
FPS=100 (off)
HighSpeed=on
USBTraffic=100


However the resulting footage is useless as it has a visible moire pattern (raw and stacked, example is stacked):

2jEHDC5.png

So from now one I will stay away from 16 bit wink.gif

 

Just out of curiosity: why is the histogram showing no RGB channels when switching to 16bit?

 

Clear skies!

raphael


Edited by SupernovaDust, 06 July 2020 - 05:03 AM.


#4 TorstenEdelmann

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Posted 06 July 2020 - 05:48 AM

 

 

Just out of curiosity: why is the histogram showing no RGB channels when switching to 16bit?

 

 

In short words because it isn't implemented grin.gif 

 

It's something which is rarely used...  As Tom already explained for planetary imaging the extra-bits in 12bit mode would only give you an advantage under nearly perfect conditions. It's simply better using 8bit and getting twice the amount of data in the same time span. For solar/lunar imaging where you have lower noise levels it could make sense but most imagers are using dedicated mono cameras in this field (e.g. h-alpha imaging doesn't make much sense using a color cam wink.gif ).   

Torsten




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