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Using Pixinsight statistics to measure image differs in pure raw versus Demosaiced

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#1 russellmm

russellmm

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Posted 26 September 2020 - 03:34 PM

I am trying to understand why when I open an image as pure raw (brings it in as gray) measures significantly lower "maximum" values versus opening it as a regular Demosaiced (RBG) raw.

 

It is supposed to be a saturated image, which opening it as regular raw shows to be true. But as a Pure Raw (gray) it's maximum value is much less.

 

 

Edit:

Changing the number from 16K to 64K in the Maximum ADU seems to only affect Full well Capacity and Dynamic Range numbers that are generated. 

 

My goals is trying to:

1. Use BasicCCDParameters to get my read noise and gain. Part of that process is inputting Maximum ADU for my DSLR (5D Mark III in this case). hence I was making an overexposed image

2. Use the data to measure my Signal Level as talked about in this thread https://www.cloudyni...-in-pixinsight/

 

 

Regards

Russell

Attached Thumbnails

  • 2020-09-26 13_20_14-PixInsight.jpg
  • 2020-09-26 13_21_06-PixInsight.jpg

Edited by russellmm, 26 September 2020 - 03:52 PM.


#2 endlessky

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Posted 26 September 2020 - 04:04 PM

I had similar goals - and problems - as you are having when I tried to do the same thing with my D5300.

 

Thread for reference: Help Me Optimizing My D5300 Capturing and Calibrating Workflow

 

Basically, even if you choose 16-bit representation in PixInsight statistics, the full well number (of undebayered, RAW image) will be the highest bit supported by your camera (in my case, it was 14 bit, so 16384).

 

Think of it as a 16 bit "container" that doesn't stretch to accomodate your data, but only store it in its first n-bit portion (where n is the number of bits of your camera RAW output).


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#3 russellmm

russellmm

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Posted 26 September 2020 - 04:52 PM

thanks, I'll take a look at your thread. My fullwell number is also well below what I would have expected to see, so I will have to figure that out as well




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