Author Topic: Basic CCD Parameters v.0.3.1 Readout Depth  (Read 219 times)

Offline freddy1

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Basic CCD Parameters v.0.3.1 Readout Depth
« on: 2017 May 15 13:37:46 »
Hello Every Body

I have a question
How is excactly the meaning of Readout Depth value? and How is the difference between this value and A/D bit ?

I have clear that A/D bit is the ADC or Analogical to Digital Converter value, which is specific for each camera, provided at camera specifications; for example Canon 450D EOS is 14bit; ZWO AISI 1600 MC is 12 or 10 bit; etc.

BUT How is Readout Depth?;  What value I must to put here?

I appreciate comments!!
Thanks
Federico
 
 

Offline Niall Saunders

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Re: Basic CCD Parameters v.0.3.1 Readout Depth
« Reply #1 on: 2017 May 15 16:07:39 »
Hi Federico,

Readout Depth is something that you can think of in the same way as the ScreenTransfer Function - it acts as a finalinterface between the 'actual' value that PixInsight is using and what you, the user, sees on the screen.

Remember, your imager may have a built-in A/D converter that is, perhaps, running at 16-bits - and so it will store 16-bit integers in the image file during capture. However, you might only have a 14-bit A/D converter - but will still probably generate 16-bit integer values in your captured data.

Then, you come to read these images into your processing program (here, naturally, you have chosen to use PixInsight). The software may choose to store the pixel values (ADU values in reality) in any suitable format whilst the image is being held in RAM - typically, PixInsight defaults to storing the ADU values as 32-bit FloatingPoint values. Further, the original range of ADU integer values might have been something like 00000 to 65535 for a 16-bit A/D digitiser. However, PI will now hold that range as a 'Real' number between 0.000000 and 1.000000 (which allows for far easier internal processing).

Then you come along, as the user, and 'you' want to know what a particular value is. But, the question is, "What range would you like to use to represent the ADU range?". You are not confined to what the camera originally provided (via its A/D circuit), nor are you even confined to what PixInsight is using internally. PixInsight will present the data to you in a format that *you* want to visualise it in.

So, you get to choose - if you choose a REAL format, PixInsight even lets you set how many decimal places you want to see. If you choose a (BINARY) INTEGER format, then you get to choose the bit-depth (8-bit, 10-bit, 12-bit, 14-bit, 16-bit, etc.) - all that PI does is to perform a quick internal calculation from the ACTUAL value to the range that you have defined. You can also define a DECIMAL INTEGER format - where the range will be from 0 to some 'power of ten' - in otherwords, the brightest pixel would be assigned a displayed value of '1', followed by the 'number of zeroes' that the user specifies.

As always, flexibility is the name of the game. PixInsight puts you in control  :D

I hope this helps, but please ask for clarification where needed.
Cheers,
Niall Saunders
Clinterty Observatories
Aberdeen, UK

Altair Astro (GSO) 10" f/8 Ritchey Chrétien CF OTA
EQ8 mount with homebrew 3D Balance and Pier
Moonfish ED80 APO
Celestron Omni XLT 120
QHY10 CCD
QHY5L-II Colour
9mm TS-OAG and Meade DSI-IIC

Offline freddy1

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Re: Basic CCD Parameters v.0.3.1 Readout Depth
« Reply #2 on: 2017 May 17 00:59:20 »
Hello Mr Niall; Thanks very much for your reply

So them (if I understood correctly): The camera ADC (Analogical to Digital Converter (in my Canon 450D 14 bit) give a 0 - 16383 differents values for all the possible electrons catched by one pixel, them this ADC range will be, by the sofware, divided  in (for example using 16 bit) at 0 to 65535 new values ranges. Right ?... so then the ratio between this two scales are : 4

I made an exaple to take the gain value camera, using b]BasicCCDPapameters[/b] 

Gain using  16 bit Readout Depth  & 14 bit ADC   = 0,155 e- / ADU
Gain using  14 bit Readout Depth  & 14 bit ADC   = 0,621 e- / ADU

 The rate between gain :  0,621/0,155 = 4

I hope I understood the subject

Thanks very much
Federico


 

Offline Niall Saunders

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Re: Basic CCD Parameters v.0.3.1 Readout Depth
« Reply #3 on: 2017 May 17 12:45:41 »
Hi Federico,

As I understand the option for the  Basic CCD Parameters Script :

You need to tick the CFA selection box
Readout Depth should be set to 16
A/D Bits should be set to 14

Then, you need to know what value is reported as the Maximum ADU value when you super-saturate an exposure (e.g. a long exposure taken during the day). The value that you want to use would be the one obtained when you open that exposure in PixInsight, and examine the image using the Readout Tool, for example.

Further, you would need to have set the readout tool, or Statistics Process, to give you the ADU value as a 16-bit Integer value (0 to 65535).

That should be all that you need (other than the images required to actually calculate the results.

In your case it is meaningless to calculate the gain for 14-bit readout depth as you are confined to 16-bit depth for your particular equipment configuration.

I hope this helps - and I am happy to stand corrected if anybody else wishes to comment.
Cheers,
Niall Saunders
Clinterty Observatories
Aberdeen, UK

Altair Astro (GSO) 10" f/8 Ritchey Chrétien CF OTA
EQ8 mount with homebrew 3D Balance and Pier
Moonfish ED80 APO
Celestron Omni XLT 120
QHY10 CCD
QHY5L-II Colour
9mm TS-OAG and Meade DSI-IIC

Offline freddy1

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Re: Basic CCD Parameters v.0.3.1 Readout Depth
« Reply #4 on: 2017 May 19 02:35:29 »
Hi Niall Thanks very much again

That´s raight as you say.
I made some a example and work very well
federico