colour saturation: not satisfied enough

[paolo speggiorin]

Hi all!
I've just start using Pixinsight to integrate and edit images taken with:
Telescope: Newton 500mm diameter F5
Camera: Sony Alpha9 full frame
I have integrated some images learning by some tutorial on the web, but I still have a problem:
--> If I work on ARW files (Sony's RAW files) I'm not able to achieve a good colour saturation, as instead I'm able to do if I work on ipg files. I'm using the tool "Color Curves" but with the files obtained from original ARW files I always see too much white and less colours...
I attach two examples of the same image of Galaxy NGC 2841 in Ursa Major, edited with Pixinsight 1.8.6 integrating jpg files and arw files.
Anyone can help me in finding what's wrong in my process? Thank you!

[ngc1535]

Paolo,

No one has yet responded- so I will give it a try.
You didn't say at what point you debayered the images.
I can imagine a situation where you register (align) images that are *not* debayered and then add them together.
The interpolation of pixels as part of the alignment process will result in the behavior you are stating.

I think you might need to be very detailed about the processing steps you used- and very likely make the image you think without color available.

-adam

[paolo speggiorin]

Thank you Adam for your help!
Here below I summarize the process I used:
- I took 30 images with Sony Alpha9 both in ARW non compressed and JPG format
- In Pixinsight I translated ARW format in XISF format (BatchFormatConversionScript)
- I intgrated the images with (BatchPreprocessing Script), with the parameters set as you can see on attached image.
-Then I applied on the resulting image (DynamicBackgroundExtraction) process
-Then I applied (Intensity Histogram Transformation) to strech the image
-Then I applied (Intensity CurveTransformation) on "S" parameter for intensity
--> it is at this point that I see the difference between the same process apllied on original ARW and JPG files.
I hope this is clear enough: please ask me anything more if necessary, than you!

[paolo speggiorin]

I forgot to specify that Integration preprocessing has been made with FLAT frames and DARK frames.

[ngc1535]

Hi again,

Too much stuff!
Does one debayered RAW image look like one JPEG (when screen stretched appropriately)?
If not, there is a problem with the bayer filter pattern assignment.

Also, I do not understand why you converted to XISF format? Why not simply load the ARW files? It is one of the supported RAW formats.

Ultimately you probably need to make a few images available.

-adam

[sharkmelley]

The colours you see in a JPG come from the various steps that the raw converter implicitly applies:

• White Balance
• Camera specific colour correction matrix to XYZ space
• Matrix conversion to Adobe RGB or sRGB colour space including white point adjustment (e.g. Bradford)
• Gamma for Adobe RGB or sRGB colour space
• Additional saturation

If you know the matrices, you can perform the same steps to your linear stacked data from BatchPreProcessing but most people don't do this.  You would need a reasonable background in colour science to obtain the matrices and apply them correctly.

However you can get reasonably close by doing the following:

• White Balance
• Background Neutralisation
• Adjust highlight point using HistogramTransformation
• Colour preserving stretch such as ArcsinhStretch
• Colour saturation to taste

Currently it is your image stretching that is bleaching the colours.  For preserving colour, an alternative to ArcsinhStretch is MaskedStretch.

Mark

[paolo speggiorin]

Adam thank you!
I tried to translate ARW into XISF because I was thinking this could help, but at the beginning I worked directly on ARW files with the same result.
Regarding on sending you some ARW images, they are very big! (around 15 Mb): how do you prefer I send them ? With "YouTransfer?

[paolo speggiorin]

Mark Thank you!
When you speak of White Balance do you mean "in the camera" or a process of Pixinsight?
Second question: I just had a look to your web site, and to the video "real time tour of the night" : very powerfull!! When you use a Modified H-alpha camera, that means wthout its original IR filter, how do you set "White Balance" parameter on the camera? Still "AWB" mode or do you create a Customized White Balance to return back to a more neutral image? (but I think in this second case you loose the light gain achieved with the filter removasl...)

[sharkmelley]

Hi Paolo,

When I refer to white balance, I mean doing it within PixInsight.  It's because I always use raw data and the white balance that is set in camera has no effect on the raw data.

My real time night sky video shot with the Sony A7S is an exception to this.  For that video, the white balance used would have been in-camera.  To be honest I'm not sure which white balance I used.

Mark

[paolo speggiorin]

OK Mark, so if I use RAW files how can I do White balance in Pixinsight?

[paolo speggiorin]

In the meantime I remade the complete process starting from ARW original files, and I'm happy to see a more natural final result expecially regarding on the colors: what do you think?
I tried to evidenziate more the details of the galaxy, using "wavelets" process, bbut I didn't achieve a visible result.

[sharkmelley]

OK Mark, so if I use RAW files how can I do White balance in Pixinsight?

ColorCalibration or PhotometricColorCalibration

Mark