PixInsight - HT shows Blue spike

[Midnight_lightning]

Hi,
Just purchased PI after brief trial and am processing M31. I have 300s lights:
Red- 8
Blue - 11
Green -12

When I go to stretch I notice the blue channel appears stronger - see image.


Prior to this I did the following.
Channel Combine of RGB stacks (pre-processed in APP)
Dynamic Crop
DBE
Noise reduction with Multiscale linear transform

I reversing the stretch, splitting the RGB, and applying linear fit but then I got a similar result in HT but with the Red signal spike.

Any thoughts, is the blue spike a problem, if so where did it arise and how do I treat it?

Thanks

Jon

[Davey-T]

Don't know if it's connected to your problem but some cameras / sensors are more sensitive to some colours.

I use Maxim and when combining RGB the colours can be weighted to offset this effect.

Dave

[Midnight_lightning]

I haven't noticed any issues using tar Tools but haven't anything to compare it with in PI as yet. I'm just wondering if M31 itself might have a blue bias - perhaps the histogram is ok?

 

[Adreneline]

Hi.

Don't know if this will help but after DBE (or ABE) I usually perofrm a BackgroundNeutralization and then a ColourCalibration (or use PhotometricColour Calibration); I follow the procedure shown in the LightVortex Tutorial - there is one specifically covering M31.

HTH

Adrian

[Jkulin]

I have been messing around with G2V, which seems to be making sense: -

HTH

[sloz1664]

As Adrian has pointed out, if using Pixinsight use PhotometricColour  or colour calibration. If you are not going to persist with Pixinsight you could try eXcalibrator. 

Steve

 

 

[wornish]

In PI after doing Dynamic Crop and DBE on each of the individual channel stacks match the image brightness with Linear Fit.

Use the brightest image as the reference image and then drop the triangle on the other two.

 

Then do the RGB combination.

[Midnight_lightning]

I had done Channel Combine before DBE, will try again doing as you say.

[wimvb]

On 01/12/2018 at 13:27, Midnight_lightning said:

Any thoughts, is the blue spike a problem, if so where did it arise and how do I treat it?

There's nothing to worry about, this is perfectly normal. The histogram shows the amount of each colour (y-direction) at a certain intensity (x-direction). The peaks represent the background. Your histogram shows a good alignment of r, g, and b; a neutral background. If at a later stage during processing, any one colour starts to dominate, you can either realign the histograms, or use scnr on that colour.

My usual workflow is:

Rgb combine, DBE, colour calibration, denoise in L only in L*a*b mode, then denoise with MMT on chrominance only. With a fairly strong mask (at least 50 %). Then I stretch the image with arcsinh, ht or masked stretch.

I don't always do linear fit, since colour calibration will also align the histograms