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[Sticky] Does astro pixel processor apply the color matrix correction to digital camera raw data?  

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(@mabula-admin)
Universe Admin
Joined: 4 years ago
Posts: 2542
March 14, 2018 19:41  

Hi @1llusiveastro,

This feauture will come soon 😉

APP 1.060 will have a new and upgraded calibration engine which has the highest priority now.

Using the camera matrix while keeping the data linear is something that no other application currently does I believe and my aim will be do to just that. The problem is getting the right colors with the camera matrix while not applying the appropriate gamma curve which affect the colors as well.

An equally as interesting feautre will be color preserving stretching, so that will come soon as well. (similar to properties of the arcsinh stretch)

Kind regards,

Mabula


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(@rudypohlgmail-com)
White Dwarf Customer
Joined: 4 years ago
Posts: 23
March 14, 2018 20:33  

Hi Mabula,

Good for you for working so persistently on APP!

Best regards,
Rudy


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(@mabula-admin)
Universe Admin
Joined: 4 years ago
Posts: 2542
March 15, 2018 11:55  

Hi Rudy @rudypohlgmail-com,

Thank you, your proposed changes for the colors with DSLR camera's will come soon after APP's next release 😉

1) applying the camera model specific matrix from camera colors  to XYZ to sRGB or Adobe 1998 while keeping the data linear

2) rebuitl the preview filters to include colro preserving stretching

First, APP 1.060 will see a major upgrade in the calibration engine...

Cheers,

Mabula


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(@jjsmith)
Hydrogen Atom Customer
Joined: 2 years ago
Posts: 1
December 31, 2018 09:25  

Hi, I recently signed up for a trial license and am using it to stack some DSLR (Canon 5DS) Raw files as I read this programme preserves the colour matrix. I understand from clarkvision.com the histogram should have separate RGB peaks and not have them aligned as one of his points to remain 'colour-accurate'. Is this possible in APP? If so, what should the appropriate settings be? I seem to get default normalized stacks and the histogram is RGB aligned into a single peak.

A second related query is for my OSC ASI094pro, it uses the same CMOS as the Nikon 810(A - also I think). How should I set the RGB  in tab 0 (raw and fits) to apply this colour matrix correctly and also to process so the final stack histogram are not auto-aligned (unless by coincidence)?

I hope the qeury is clear as I am not very technical, so please feel free to ask if any clarification is needed. Many thanks!


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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3197
January 2, 2019 22:22  

Just having peaks aligned isn't necessarily "colour-correct", nothing is really. 🙂 But you can say that we do know the wavelengths belonging to certain elements and you can use these things to kind of get a natural look. But people like to change that to others just because it looks nicer to them. To get a kind of accurate, natural starting point you can use the color correction tool in the 'Tools tab (9)' and play a bit with that, it's used at the end of the processing.

Second query I don't quite understand, does APP not automatically give you the correct pattern for that camera? If not you would have to look up the pattern in the sensor details of the manufacturer and apply it in that tab.


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(@mabula-admin)
Universe Admin
Joined: 4 years ago
Posts: 2542
January 20, 2019 16:08  

Hi @jjsmith & @vincent-mod,

Hi, I recently signed up for a trial license and am using it to stack some DSLR (Canon 5DS) Raw files as I read this programme preserves the colour matrix. I understand from clarkvision.com the histogram should have separate RGB peaks and not have them aligned as one of his points to remain 'colour-accurate'. Is this possible in APP? If so, what should the appropriate settings be? I seem to get default normalized stacks and the histogram is RGB aligned into a single peak.

Off course, the information that you mention as provided by Clarkvision is in this case rather confusing and also rather incomplete I would say. It really depends on the data. To get accurate colors, severals processing steps need to be taken as well.

If you have data without any nebulosity showing, of for instance a regular star cluster like the double cluster then the statement "the histogram should have separate RGB peaks and not have them aligned" really is not very valid I think.

In that particular case, of no nebulosity present, the sky background is represented by the peaks in your histogram and for background calibration you really expect them to have the peaks aligned. For data with clear nebulosity however you really can't trust the location of the histogram peaks as an nidication of proper background calibration.

Now what happens in APP with normalization for color data is that, by default, the background is neutralized (which you can easily switch off). This will not harm your data and also is not proper background calibration. Background neutralization is a histogram operation and for data with nebulosity, you will see that it is not the same as background calibration. Proper background calibration can be done with a separate tool in APP in menu 9).

Further more, proper star colors will only be achieved after proper background calibration and the Star Color Calibration module in APP will even correct the sky background again in that case.

So it actually is a lot more complicated then simply stating "the histogram should have separate RGB peaks and not have them aligned" because there is data that will actually need the peaks to be aligned for proper colors. And then you have the question, what is proper color ? Is that the color that your camera sees (each sensor sees the world differently)? Is that the color that your eyes would see ? In addition, the used filters will again have effects that really will change color as perceived by your camera... Star Color Calibration needs to take into account the filters as well.

A second related query is for my OSC ASI094pro, it uses the same CMOS as the Nikon 810(A - also I think). How should I set the RGB in tab 0 (raw and fits) to apply this colour matrix correctly and also to process so the final stack histogram are not auto-aligned (unless by coincidence)?

For the asi094pro it depends on the capture software used what you need to do. IN most cases, the capture software will not store metadata about the data being from a Bayer CFA sensor, so will you need to enable Force Bayer CFA in 0) Raw/FITS and you will need to set the correct Bayer Pattern as well to get proper data processing.

Please let me know if you have additional questions.

Mabula

This post was modified 2 years ago by Mabula-Admin

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(@jethro777)
Molecular Cloud Customer
Joined: 2 years ago
Posts: 3
June 30, 2019 08:16  

Just to follow up on this, is the ability to adjust for the cameras color response as per sharkmelly's comments now possible?

Where, when and how is this done, assuming you have the 3x3 matrix available?


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(@euripides)
White Dwarf Customer
Joined: 1 year ago
Posts: 18
December 5, 2020 08:57  

I was reading about the method at clarkvision.com and just found this topic here too 🙂

As I can see it is a command line tool and I need to test it - I am in the middle of an M31 integration at the moment - but it would be really interesting if this is already “part” of our APP 🙂 


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(@theo950)
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Joined: 5 months ago
Posts: 2
February 28, 2021 18:03  
Posted by: @mabula-admin

Thank you, your proposed changes for the colors with DSLR camera's will come soon after APP's next release 

1) applying the camera model specific matrix from camera colors  to XYZ to sRGB or Adobe 1998 while keeping the data linear

2) rebuitl the preview filters to include colro preserving stretching

Hi Mabula, I am relatively new to AP and have been using APP for (pre-)processing. Lately, I got interested in attempting to develop a colour calibrated workflow and found this thread (and the original one on CN).

Has the feature mentionned above yet been implemented in APP? 1) performing a colour matrix correction + gamma-curve on the integrated data, 2) correct for the effect of the gamma-curve on the luminance (as Mark Shelley pointed out), to preserve the linearity of the data.

If so, when does it take place during the whole process? If I've understood it well, CM+gamma should be applied after background extraction and calibration. Is this correct? Is there a way we could choose to either perform or noot perform these corrections on the data?

Best regards,

Théo


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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3197
March 1, 2021 10:29  

Yes, they have been in APP since that release basically, but internally applied in the algorithms. For the preview filter this is applied when loading in a light frame to preview and other I'm not really sure about, but likely early in the process as well. These have been working very reliable now for quite a while, color correction is then best to achieve with the color correction tool, given you use broadband data (not narrowband).


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(@jochen-scharmann)
White Dwarf Customer
Joined: 2 years ago
Posts: 12
March 1, 2021 19:44  

Hi,

In the RAW tab, APP still shows R;G;B factors all @ 1,0 and there is no indication of the Matrix correction whatsoever. 

Is there a way to unselect the Matrix correction to keep the stack as "raw" as possible?

I would like to apply Matrix correction in my after processing in StarTools.

regards,

jochen


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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3197
March 1, 2021 19:50  

Let me ask Mabula for this specifically, I may be wrong there...


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(@mabula-admin)
Universe Admin
Joined: 4 years ago
Posts: 2542
March 4, 2021 14:12  

Hi @theo950 & @jochen-scharmann & @vincent-mod,

No, the color matrix is not yet applied in Astro Pixel Processor. It is hardly a trivial task as well, but it will soon be introduced in APP now that we support almost all raw formats in APP using Libraw. Thanks to Libraw and our testing, we now know for all camera models the color matrix and you can actually see that in the latest APP version in the console window when you load a consumer camera RAW frame:

A canon EOS 5DS R CR2:

Console Raw Conversion Details

Jochen, the RGB factors are there so that you can adjust/overrule camera white balance yourself 😉 they have nothing to do with the camera matrix.

Kind regards,

Mabula


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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3197
March 4, 2021 14:26  

Ah there we go, woopsie from my part.


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(@jochen-scharmann)
White Dwarf Customer
Joined: 2 years ago
Posts: 12
March 4, 2021 17:01  

Thanks Mabula,

got it, but once it will be introduced, will there be an option to disable Matrix correction? 

jochen


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