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ASI 120 MC color balance and exposure settings

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#1 urassner

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Posted 05 January 2014 - 07:14 PM

Due to 2 issues I had when imaging Mars and Jupiter with my setup, I decided to look into the settings for my ASI 120 MC when using firecapture.
1. Last time when imaging Mars, the red channel was overexposed and the least sharp, even though my histogram in Firecapture showed only about 50% when imaging. The unsharpness might at least in part have been caused by the inversion we were having at the time, however that would not explain the over exposure.
2. Jupiter had a slight blue/green tint and the moons of Jupiter also looked blue/greenish.

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#2 urassner

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Posted 05 January 2014 - 07:16 PM

I mounted the camera with a UV/IR filter on a tripod facing down, close to a white piece of paper with direct sunlight falling onto the paper.
With this setup I checked different exposures and color balance.

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#3 urassner

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Posted 05 January 2014 - 07:24 PM

I normally have the debayer checkbox not checked in firecapture, to minimize the file size. Debayering is done in Autostakkert, using the auto setting. For this test I checked the debayer checkbox and realized, that it then shows individual histograms for red, blue and green channels.
Two things stood out to me:
1. Even though I was using a white piece of paper in sunlight ( I thought this to be the closest to the color balance I would need, as the planets reflect sunlight), the histograms were not superimposed, and the resulting image on the screen had a slight but definite blueish tint (confirmed by measuring RGB components in photoshop).
2. When increasing exposure time with gain set to 0, the red and green channel hit maximum at 50% (128 max) for green and 47% (120 max) for red. Further increasing the exposure time, resulted in a more pronounced blue tint of the image with finally blue hitting maximum at 84% (215 max). This was all done with the standard settings.

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#4 urassner

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Posted 05 January 2014 - 07:26 PM

I went into the pull down menu to adjust the color weighting and reduced the blue weighting and increased the red weighting, until the histogram bell curves for red, blue and green were superimposed, which removed the blue tint in the image.
I actually opened the door for this, so that no color error would be introduced through the glass of the window. It changed the color balance slightly.

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#5 urassner

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Posted 05 January 2014 - 07:30 PM

I am hoping for some clear skies tonight, to do some real live test images of Jupiter and maybe Mars tomorrow morning.
I will still image in non-debayer mode, however to set the exposure, I will turn on the debayer option and carefully checked the color histogram to ensure that non of the channels are overexposed (indicated by a single line or truncated bell curve in the histogram.

Please let me know your thoughts.

#6 Mert

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Posted 06 January 2014 - 04:42 AM

I usually do the White balancing before imaging, last time
imaging Jupiter even with the RGB balance option in Registax
nothing changed anymore and the colors look ok to me.
This is the way to go I think.
Once done, sabe your settings into a file and when imaging
just load this settings file and done I think.

#7 urassner

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Posted 06 January 2014 - 11:17 AM

Thanks for your input, Mert. What do you use for your white balance ? I did some imaging last night and this morning. Transparency was good (inversion is gone for now), but seeing was intermediate. However, things look improved. I kept the read and green channel at 40% so I would not overexpose them. This are just some preliminary processing, but I feel, things are moving in the right direction.

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#8 HowardK

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Posted 06 January 2014 - 02:14 PM

Interesting

Please keep postings with how u use Firecapture with the ASI 120MC

#9 Mert

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Posted 06 January 2014 - 05:21 PM

Hi Ulrich,

From the log-files of Firecapture:
WBlue=86
USBTraffic=59
Gain=72
AutoExposure=off
Gamma=50
WRed=54

So Red 54 and Blue 86 in my case. ( mileage may vary
according equipment and conditions used :) )

Hope it helps

#10 urassner

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Posted 07 January 2014 - 09:56 AM

Mert, thank you for this information. How do you go about white balancing your camera? Do you use sunlight, moon (assuming the moon is truly grey)?
I have been happier with the adjusted settings and the greenish color of the moons of Jupiter seems improved, however, Saturn now seems to have a slight greenish tint.
Unfortunately, weather will force a delay in further investigation.

#11 Mert

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Posted 07 January 2014 - 03:34 PM

Hi Ulrich,

I normally check on the ceiling ( White ) with some lights
switched on.
If out in the field, I use an empty "notepad" screen on
my laptop and let the camera look at this.
Then I merely adjust the sliders until the same color is
displayed on FC screen and as seen with my eyes.
It's not very scientifical but serves for me :shrug:

When doing wavelets etc. in Registax you can use the
RGB-balance button and done with it, that's all I do
to it to obtain my final images.

#12 urassner

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Posted 08 January 2014 - 12:20 AM

Hi Mert, thanks for the info. I had actually first tried to check the camera by displaying red, blue and green on my computer monitor (using photoshop and setting RGB to 255 R, 0 G, 0 B and so forth), but was shocked how different the red looked on the preview screen and also saw 2 peaks in the histogram.
That is why I decided to use sunlight, as that is the light that illuminates the planets. It actually made even a little bit of difference whether it was sunlight coming through the window, which does not appear tinted to me) or with window open.
I will try to compare the RGB curves with different artificial light sources.

#13 PhilCo126

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Posted 02 April 2014 - 11:05 AM

interesting topic... which telescope was used in the first post?

#14 Angela G

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Posted 02 April 2014 - 02:21 PM

When using my ASI120MC I typically get the histogram to the level that I want to capture at. Then I begin balancing the color channels. Since Red and Blue are the only channels you can adjust, I adjust them to approximately the same level as the green channel.

I recommend waiting until you are looking at your target to adjust your color balance. Varying atmospheric conditions will require different adjustments. For instance the blue channel will need to be set higher if there is thin cloud cover. The elevation of the planet (which effects the amount of atmosphere you image through) also effects your color balance.


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