Manual Demosaic Setup for asi071 in Nebulosity?

bent

What settings do you use for the Manual Demsaic Setup in Nebulosity for the ASI071?

bent

Never mind, I decided to just go with the whatever comes out with ZWO ASI camera, do an Auto Color Balance after the demosaic process, and go from there.

wilcogr1

I had difficulty in finding this, following my first imaging session with my newly-purchased ASI071 a couple of days ago.

Although there were no issues in Nebulosity recognising the camera characteristics during imaging, when it came to Demosaicing and transforming to colour, I was presented with the manual option.

I worked through the various RGB array offset values with an image of M27 (Dumbbell Nebula) in Vulpecula, as the main part of the nebula should be (largely) blue-green, while the outer fringes should be H-Alpha red.

All four options were trialled: X=0 Y=0 / X1Y0 / X0Y1 / X1Y1.

The best fit was definitely X=1 Y-1

This topic is documented in the Nebulosity 4 manual (April 2015) on page 50.

bent

wilcogr1 wrote:
I had difficulty in finding this, following my first imaging session with my newly-purchased ASI071 a couple of days ago.

Although there were no issues in Nebulosity recognising the camera characteristics during imaging, when it came to Demosaicing and transforming to colour, I was presented with the manual option.

I worked through the various RGB array offset values with an image of M27 (Dumbbell Nebula) in Vulpecula, as the main part of the nebula should be (largely) blue-green, while the outer fringes should be H-Alpha red.

All four options were trialled: X=0 Y=0 / X1Y0 / X0Y1 / X1Y1.

The best fit was definitely X=1 Y-1

This topic is documented in the Nebulosity 4 manual (April 2015) on page 50.

Thanks wilcogr1,

I agree with you, x=1, y=1 gives the best results, but that still leaves a moderate blue color cast for me. Auto Color Balance quickly fixes this. I wonder is ther are any settings in the RGB “Color Control” array that would counter act this color cast to begin with?

wilcogr1

Logically, I think that this could only be set in Nebulosity through Edit -> Preferences, in the Capture Output or Processing sections - but I don't see anything obvious there.

There is an option for altering the demosaic method. The default is VNG, but I have no idea whether changing this will alter the colour balance in any significant way - I guess that the only way is to try out these variations. See manual page 104.

I tend not to use the Auto Color Balance step in Nebulosity, instead relying on Photoshop to remove any imbalance further downstream - as there is a lot more control there. I have Photoshop's Camera Raw configured to process 16-bit Tiffs in addition to Raw, so get several bites of the cherry in my workflow.

In addition, if there is extensive image manipulation taking place during the workflow, it could be argued that there is almost certain to be RGB channel imbalances introduced anyway - which are best neutralised near the end.

But I do use the Adjust Color Background menu item, to neutralise any imbalance caused by skyglow.

Cheers,

Graham

bent

Graham, Thanks for pointing out that manual override in preferences noted on page 104. I missed that little tidbit. What I was wondering if anyone has fooled around with the numbers Color Control array in Manual Demosaic Setup dialogue box (seen on page 50) to remove color casts. See attached screen capture:

wilcogr1

Ah, I see. My immediate response is that I have no idea - maybe this thread will be picked up by someone who has.

My gut feeling, after quite a few years of Photoshop usage, is that a 10% alteration in the channel mix would produce a distinct change in the colour balance - enough to see whether it was worth progressing.

Cheers,

Graham

bent

I figured out a major mistake I was making which in retrospect seems obvious. It was causing a variable color cast. I was aligning and combining before doing the de-mosiac processing.....oops : Now as least it seems like I getting the same blue color cast each time which could be some minor residual moon light when I shot the Adromeda Galaxy. It was about a half moon which had not quite set for the image stack that I'm experimenting with. Also I live in a moderately heavy light polluted area. I was using an Orion SkyGlow filter. Oh well, you learn best from your mistakes.

bent

Here is a version with Nebulosity pre processing and levels stretching but otherwise no post processing.

Expsosure 300sec (per light frame), gain 200, offset 100, -10C. Aprrox 15 lights, flats, darks, bias frames. I did the a batch de-mosaic before aligning. I used a Bad Pixel Map of my master dark frame for dark noise removal. I did a align without combine followed by combine with 1.25 standard deviation stack.

It was a lower humidity night so I was able to go down to -10C without sensor frost or dew on the front window.