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INDI Library v2.0.0 Released (01 Feb 2023)

Bi-monthly release with major changes to INDI properties and client API in addition to new drivers and improvements.

ASI183MM PRO Offset

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Hi,

I came across an issue with my ASI's offset setting. The thing is It's very unpractical that the offset value doesn't end up in the FITS Header. Would it be possible to add this feature to Ekos, or is this a driver thing? The driver might have some other issues as well. Another one is that while my camera has a 12bit ADC my only options in the controls are 8 and 16 bit. Anyone here using the same camera with Ekos? I would be thankful if you could help me!

Thanks,
Florian
Hetes Astronomical Observatory (under construction)

Sky-Watcher Quattro 10CF 10" f/4 or Sky-Watcher 150P 6" f/5 with ZWO ASI 183MM PRO, ZWO 8x1,25 EFW,
ZWO ASI 290MM Mini and OAG on Sky-Watcher AZ-EQ6 GT with EKOS on Raspberry Pi 4

Sky-Watcher Esprit 80ED with Canon 600D and Lacerta M-gen
3 years 2 weeks ago #48188

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Replied by Dirk on topic ASI183MM PRO Offset

Hello,
I agree that it would be nice to have the offset value in the FITS Header.
EKO, and most other astrophotography tools have two ways to handle image data, 1 or 2 Byte per file, thus 8 or 16 bit. I doubt, that the fits format would even allow 12 bit files. 8, 16 and I think even 32 used more or less widely.
While the camera delivers 12 bit values, the remaining 4 bits are filled with zeros, effectively multiplying the value with 16. So you will have values in the range of 0 to 65535 instead of 0 to 4095 but all you values are multiples of 16.

So in short, I you do not want to use 8 bit, chose 16 and you will receive what you camera delivers.

Regards

Dirk.
iOptron CEM25P
Skywatcher Evostar 72 ED DSPro
Explore Scientific ED 102
ASI 1600Mm Pro ASI EFW Mini
QHY 8L
DeepSky Dad AF1 motor focus
ASI 120MM Mini and Bresser (Touptek) 290 Guidecams
Sykwatch EvoGuide 50/242 and NoName 50/175 Guidescopes
Raspberry Pi 3 and 4
The following user(s) said Thank You: Florian Vamosi
3 years 2 weeks ago #48192

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Replied by Jasem Mutlaq on topic ASI183MM PRO Offset

Sure it can be added. What's the standard FITS keyword for this?
Jasem Mutlaq
Support INDI & Ekos; Get StellarMate Astrophotography Gadget.
How to Submit Logs when you have problems?
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The following user(s) said Thank You: Florian Vamosi
3 years 2 weeks ago #48207

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Replied by Dirk on topic ASI183MM PRO Offset

Hello Jasem,
for gain I found to more or less standard keywords, which are GAIN or EGAIN, both measured in e-/ADU, for offset I could not find anything commonly used. In ccdciel, Patrick Chevalley decided to add following headers to fits files for Indi controlled cameras:

+ if gain>0 then Ffits.Header.Add('GAIN',gain,'Video gain');
+ if gamma>0 then Ffits.Header.Add('GAMMA',gamma,'Video gamma');
+ if offset>0 then Ffits.Header.Add('OFFSET',offset,'Video offset,brightness');

(sourceforge.net/p/ccdciel/code/602/)

which was the only useful reference I could find...


Regards

Dirk
iOptron CEM25P
Skywatcher Evostar 72 ED DSPro
Explore Scientific ED 102
ASI 1600Mm Pro ASI EFW Mini
QHY 8L
DeepSky Dad AF1 motor focus
ASI 120MM Mini and Bresser (Touptek) 290 Guidecams
Sykwatch EvoGuide 50/242 and NoName 50/175 Guidescopes
Raspberry Pi 3 and 4
3 years 2 weeks ago #48440

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hi!

shouldn't the offset be listed with the BZERO keyword in FITS???
yours wolfi
3 years 2 weeks ago #48441

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Replied by Dirk on topic ASI183MM PRO Offset

I understood this value is for the conversion of signed int to unsigned int

Regards
Dirk
iOptron CEM25P
Skywatcher Evostar 72 ED DSPro
Explore Scientific ED 102
ASI 1600Mm Pro ASI EFW Mini
QHY 8L
DeepSky Dad AF1 motor focus
ASI 120MM Mini and Bresser (Touptek) 290 Guidecams
Sykwatch EvoGuide 50/242 and NoName 50/175 Guidescopes
Raspberry Pi 3 and 4
3 years 2 weeks ago #48443

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Hi! Sure?

KEYWORD: BZERO
REFERENCE: FITS Standard
STATUS: reserved
HDU: image
VALUE: real
DEFAULT: 0.0
COMMENT: zero point in scaling equation
DEFINITION: This keyword shall be used, along with the BSCALE keyword,
when the array pixel values are not the true physical values, to
transform the primary data array values to the true values using the
equation: physical_value = BZERO + BSCALE * array_value. The value field
shall contain a floating point number representing the physical value
corresponding to an array value of zero. The default value for this
keyword is 0.0.
Yours wolfi
3 years 2 weeks ago #48445

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Replied by Dirk on topic ASI183MM PRO Offset

Hi wolfi,
Here is what IFound:
One shortcoming of the FITS standard is that the 16-bit number format is signed, producing a range of -32768 to +32767. The range of data from many cameras is 0 to 65535. To overcome this problem, MaxIm DL subtracts 32768 from each pixel prior to saving. The FITS standard requires that the BZERO and BSCALE keywords be used when the value in the array is not the physical value; MaxIm DL sets BZERO to 32768 and BSCALE to 1. Other applications that interpret these keywords correctly should automatically add 32768 to the image pixels, resulting in a correct image display. This default behavior can be overridden using the File menu Settings command.

But I agree, with bzero = offset and bscale =inverse gain you could even produce fits files containing the number of electrons per pixel....

Regards

Dirk
iOptron CEM25P
Skywatcher Evostar 72 ED DSPro
Explore Scientific ED 102
ASI 1600Mm Pro ASI EFW Mini
QHY 8L
DeepSky Dad AF1 motor focus
ASI 120MM Mini and Bresser (Touptek) 290 Guidecams
Sykwatch EvoGuide 50/242 and NoName 50/175 Guidescopes
Raspberry Pi 3 and 4
3 years 2 weeks ago #48455

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hi!
true, but basically, this is the offset, isn't it? for the zwo cameras, it is reported correctly as 32xxx and if subtracted, this allows for rescaling of the 16 bit data from the raw BLOB as received by INDI ...
yours wolfi
3 years 2 weeks ago #48457

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No, the offset the TO talks about is the internal offset of the DA converter of the camera to prevent negative values (due to RO noise). So it's some instrument specific setting, just like GAIN (which isn't an official FITS keyword...). BZERO/BSCALE are (only) intended to modify the data, often to make better use of the storage format (like the 32768/1 setting to store UINT data as INT).
ZWO uses BRIGHT to store this offset in their FITS files (e.g., from ASICAP). But I'd just use OFFSET, like in ccdciel. It's not reserved, and then it's already (at least) two programs using it ;)
openSUSE Tumbleweed KStars git INDI git
GPDX+EQMOD, CEM60EC, ASI2600/1600/290mini+EFW+EAF
The following user(s) said Thank You: Dirk
3 years 1 week ago #48512

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Replied by Florian Vamosi on topic ASI183MM PRO Offset

Hi,

Thank you all for the discussion! Sorry to answer a bit late. Yes I was asking about the DA converter offset. I think too, that using OFFSET as the keyword, just like CCDCiel(and I think Astroart and Maxim, but I'm not sure ) would be a perfect as it is straight-forward and easy to understand. I would be thankful if you could add it Jasem! About the bit depth I was just unsure, because I saw other ZWO cameras, like the 294 having a 14bit setting, but there is no problem with the raw files so I am not concerned really.

All the best,
Florian
Hetes Astronomical Observatory (under construction)

Sky-Watcher Quattro 10CF 10" f/4 or Sky-Watcher 150P 6" f/5 with ZWO ASI 183MM PRO, ZWO 8x1,25 EFW,
ZWO ASI 290MM Mini and OAG on Sky-Watcher AZ-EQ6 GT with EKOS on Raspberry Pi 4

Sky-Watcher Esprit 80ED with Canon 600D and Lacerta M-gen
3 years 1 week ago #48533

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Replied by Jasem Mutlaq on topic ASI183MM PRO Offset

Thanks for the feedback, it's now added to GIT. Please test and report back.
Jasem Mutlaq
Support INDI & Ekos; Get StellarMate Astrophotography Gadget.
How to Submit Logs when you have problems?
Add your observatory info
The following user(s) said Thank You: Peter Sütterlin, Florian Vamosi
3 years 1 week ago #48562

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