Author Topic: How the darkframe substraction procedure is implemented?  (Read 521 times)

kaklik

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How the darkframe substraction procedure is implemented?
« on: June 09, 2022, 03:27:35 AM »
Hello,

for the scientific application, I need to know the exact way, and how the data from the sensor are processed. We made some attempts to analyze that directly from the camera output.  Our results are:
  • Camera substracts darkframe even in case of "RAW" data output
  • There is no exact control of what darkframe file is actually or has been used for the substraction

Especially the first point is quite strange because the 'RAW' data are supposed to be RAW, therefore we expect unprocessed values directly from the image sensor. Is there some option to disable dark frame subtraction at the least for raw12 data output? Where is the darkframe or black calibration applied? Is there some other processing made on "RAW" data? Is there a possibility to backup the required data and process the image outside from camera?

I'm attaching the screenshot where the subtraction of intentionally incorrect dark-frame is visible in all output formats (RAW12bit, TIFF, TIFF-RAW)
   

« Last Edit: June 09, 2022, 03:31:02 AM by kaklik »

Nikon1

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Re: How the darkframe substraction procedure is implemented?
« Reply #1 on: June 09, 2022, 03:56:37 AM »
Just two Questions:
 Are there Even Cameras that let you see / Modify the Darkframe / Sensor Calibration Data which it internally uses to process its image data, and if there are, what would anyone use that for?
 You are also aware, that there already usually is quite a bit of processing, that is happening before Cameras save an image, even in RAW format, like for example Removal of Dead Pixels and so on ( https://de.wikipedia.org/wiki/Pixelfehler#Pixelfehler_in_der_Digitalkamera ), and most likely a bunch more nobody cares about in average day to day use?
 .
 To answer your Question, i highly doubt that anyone except a few people from Krontech know whats actually going on inside the Camera regards such Specific Things as exact Sensor Data Post Processing, so probably try to ask them Directly if you for some Reason really need to know.
 Closest Thing i can Provide is some things i know from messing around a bunch on my own, and that is probably something along the lines of:
 Raw Sensor Data --> Column Gain Calibration Data --> Black Calibration Data --> [Further Internal Processing / Denoising?] --> [Color Matrix / White Balance Settings?] --> Cinema DNG
 But i cant provide any further insight into HOW exactly any of these Are Generated or how they are used to Process the image.
 Have Posted a bunch of things before, when messing around with shooting stuff without Black Calibration or Stacking "dark" Frames, and Probably will sometime soon start also playing around a bit with Column gain Calibration Data, as the New Firmware Versions now allow to do that. I can Link those here, if you have not seen them yet.

kaklik

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Re: How the darkframe substraction procedure is implemented?
« Reply #2 on: September 11, 2022, 02:43:12 AM »
Just two Questions:
 Are there Even Cameras that let you see / Modify the Darkframe / Sensor Calibration Data which it internally uses to process its image data, and if there are, what would anyone use that for?
 You are also aware, that there already usually is quite a bit of processing, that is happening before Cameras save an image, even in RAW format, like for example Removal of Dead Pixels and so on ( https://de.wikipedia.org/wiki/Pixelfehler#Pixelfehler_in_der_Digitalkamera ), and most likely a bunch more nobody cares about in average day to day use?
 .

Of course, there are plenty of cameras for astronomers, which are a good example of scientist which really needs raw data from the image sensor. For an example of these cameras look at: https://www.gxccd.com/

Is there an option (even in the case of modifying the camera calibration files) to completely disable the image "enhancement" pipeline in the Chronos camera?

Nikon1

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Re: How the darkframe substraction procedure is implemented?
« Reply #3 on: September 11, 2022, 04:10:02 AM »
Ok, was not aware of these Cameras, but kinda makes sense Astro-People would have Products Like that. Never came Across Those so far.
 That website you linked is really not easy to navigate, cant find any proper Datasheet / Full Technical Data overview for any of these Cameras from a brief look; but if you say so, its Probably true that these would Provide something close to actual "RAW Sensor Data".
 .
 If you need this for some reason, i suggest one of these two things:
 .
 Get your Hands on the Oldest Firmware Possible, as these had way less advanced Processing of the Image Data. Modify at need, The Firmware is open Source. I am no Programmer, and if you are also not, get some help from someone who is.
 .
 Other Option would be to ask Krontech via their Support. I highly doubt that there is any option to just straight up turn off all Image Processing via the Camera GUI, but maybe there is some Quick Modification you can do to the Firmware via Console or something, like this Mod here:
 https://forum.krontech.ca/index.php?topic=661.msg4585#msg4585
 That way, if it works, you could save yourself a bunch of actual Coding.
 .
 .
 If you find a way, consider sharing it here, in case someone else also needs unprocessed Footage.
 

Nikon1

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Re: How the darkframe substraction procedure is implemented?
« Reply #4 on: September 11, 2022, 04:42:00 AM »
Read a little more about these Cameras, seems like they (or at least some of them) are thermoelectrically cooled, and you can fully control Sensor Temperature?
 That is a Nice Feature, have to say.
 If you happen to own one of these, what kind of Sensor Temperature would you typically want to run these at?
 Also how much of an issue is Condensation, and if Condensation is Happening, what to do against it?

kaklik

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Re: How the darkframe substraction procedure is implemented?
« Reply #5 on: September 11, 2022, 01:05:18 PM »
Read a little more about these Cameras, seems like they (or at least some of them) are thermoelectrically cooled, and you can fully control Sensor Temperature?
 That is a Nice Feature, have to say.
 If you happen to own one of these, what kind of Sensor Temperature would you typically want to run these at?
 Also how much of an issue is Condensation, and if Condensation is Happening, what to do against it?

A will reply to private messages, to keep the focus on the actual topic there.

kaklik

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Re: How the darkframe substraction procedure is implemented?
« Reply #6 on: September 11, 2022, 01:59:47 PM »

 .
 Other Option would be to ask Krontech via their Support. I highly doubt that there is an option to just straight up turn off all Image Processing via the Camera GUI, but maybe there is some Quick Modification you can do to the Firmware via Console or something, like this Mod here:
 https://forum.krontech.ca/index.php?topic=661.msg4585#msg4585
 That way, if it works, you could save yourself a bunch of actual Coding.
 .

I had ask Kronech and hope they will reply in some time.  But there will be a huge help if there will be someone who knows where calibration data are stored in the camera and what neutral calibration data looks like. In that situation calibration files could be replaced by neutral, which effectively disables the image processing pipeline. (But unfortunately does not save the processing time, because the image processing happens, but does not modify the image)

Nikon1

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Re: How the darkframe substraction procedure is implemented?
« Reply #7 on: September 11, 2022, 03:30:31 PM »
you could have a look through the Files yourself like this:
 https://forum.krontech.ca/index.php?topic=667.msg4484#msg4484
 .
 The Calibration Data can be exported to a USB Drive, that should help find the Files or Files Alike on the SD-Card.

muringuets

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Re: How the darkframe substraction procedure is implemented?
« Reply #8 on: September 13, 2022, 05:05:09 AM »
Following the discussion here, interesting points kaklik, I do astrophotography myself, never connected the dots on the calibration  the Chronos does...

I own a astro camera with built in cooling. It's simply a peltier, a temperature sensor, and some coding... oh and a good power supply, it usually takes 3 amps at 12V.

It would be awesome to have that kind of funcionality on the Chronos, but certainly at the cost of mobility, anyway it would be nice to have the feature, and be able to not use it while running on batteries...

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