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Why are my raw images so green?

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#1 delalaym

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Posted 18 April 2019 - 11:46 PM

Hi,

 

I have a C6 and a ASI224MC.

 

I was taking stills of 5s of M5 at 350 gain in RAW16 using SharpCap. 

 

On the screen, the images had a strong green tinge to it... 

 

The raw files were in PNG and I used PIPP to debayer them and here's what it looks like... (I used RGGB as I've read that this the pattern of the 224MC).

 

Am I doing something wrong?

 

Thanks!

 

Marc-Andre

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Edited by delalaym, 18 April 2019 - 11:48 PM.


#2 Jon Rista

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Posted 18 April 2019 - 11:57 PM

You are not doing anything wrong. The data just needs to be color calibrated. Most DSLRs would actually produce greenish images like this if it were not for automatic baseline color calibration that is integrated into most standard RAW image processors. A basic matrix transformation corrects the color of most RGGB (or other bayer pattern) image sensors when a RAW image is rendered to a screen or saved to a JPEG. 

 

This automatic calibration does not happen with astrophotography, so calibration must be done explicitly. I am not familiar with how PIPP works (although I am familiar with the program). I would look for any kind of color calibration tools. If it does not have any, then I would start by trying to align the black and white points of each channel in whatever histogram tool it has. If PIPP doesn't have any of these tools, then you can use Photoshop or PixInsight or other programs to calibrate. With PS, you can do the same tehing, align the white and black points of each channel (and you may also need to adjust teh histogram peaks of each channel as well).

 

If you have PixInsight, it has much more advanced and accurate color calibration tools such as ColorCalibration and PhotometricColorCalibration which will give you very good color. 


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#3 delalaym

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Posted 19 April 2019 - 01:31 AM

You are not doing anything wrong. The data just needs to be color calibrated. Most DSLRs would actually produce greenish images like this if it were not for automatic baseline color calibration that is integrated into most standard RAW image processors. A basic matrix transformation corrects the color of most RGGB (or other bayer pattern) image sensors when a RAW image is rendered to a screen or saved to a JPEG. 

 

This automatic calibration does not happen with astrophotography, so calibration must be done explicitly. I am not familiar with how PIPP works (although I am familiar with the program). I would look for any kind of color calibration tools. If it does not have any, then I would start by trying to align the black and white points of each channel in whatever histogram tool it has. If PIPP doesn't have any of these tools, then you can use Photoshop or PixInsight or other programs to calibrate. With PS, you can do the same tehing, align the white and black points of each channel (and you may also need to adjust teh histogram peaks of each channel as well).

 

If you have PixInsight, it has much more advanced and accurate color calibration tools such as ColorCalibration and PhotometricColorCalibration which will give you very good color. 

Thank you! That's helpful. :-)



#4 sg6

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Posted 19 April 2019 - 02:40 AM

As Jon says the data need calibrating - assuming that is the term, likely several. DSLR's do a bit more then just reproduce what falls on the sensor. The red band being another that needs reworking owing to the internal filters.

 

The other reason being that the sensor likely has a row of Red-Green-Red-Green.... pixels. THe n under that row of Blue-Green-Blue-Green.... pixels.

 

All nice but it means you have 1 Red, ! Blue and 2 Green by ratio. You have twice as many Green pixels as either Red or Blue. So what you get before software gets at it all is a predominence of Green.



#5 RandallK

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Posted 21 April 2019 - 07:18 PM

Hope you don't mind...I did a few adjustments in Photoshop CS6...by using the HLVG Plug-In (Green removal); Levels Adjustments, Gaussian Blurr (for background noise reduction).

 

post-306330-0-69143100-1555649180CNRK.jpg

 

Randall



#6 Stargazer3236

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Posted 02 May 2019 - 04:18 PM

In SharpCap 3.2 Pro, in the histogram tab, there are 4 color sliders on the right hand side. Underneath the color sliders are 3 icons. If you click the icon shaped like a lightning bolt, that will color correct your images, based on the star colors in your field of view. The far right slider is color saturation. You can move it up to increase the color, or move it down to decrease the color.



#7 bobzeq25

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Posted 02 May 2019 - 06:32 PM

Look at the spectrum of a typical one shot color camera (scroll down just a bit).  Anything under the green curve will be recorded as green.  Including the blue and red stuff.

 

https://www.dxomark....ry/color-depth/

 

Yet another example of why terrestrial stuff often does not apply to astro.  That spectrum, and 50% green pixels, works well for terrestrial.

 

Color needs to be managed in astro processing, and it's a complicated skill that takes time to learn.  Many astro specific programs, like StarTools and PixInsight, have specific tools to take out excess green.

 

Much more about color and its management in this highly recommended book.

 

https://www.amazon.c...d/dp/0999470906


Edited by bobzeq25, 02 May 2019 - 06:34 PM.



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