Pixinsight: synthetic luminance question

[konstantinos75]

Hi

Just a question about the synthetic Luminance frame in Pixinsight.
I have at my disposal these fit frames
- 20 red frames, bin 1x1
- 20 green frames, bin 1x1
- 20 blue frames, bin 1x1

These frames are already calibrated.

What are the steps to create the synthetic Luminance frame?
I want to use LRGBcombination module afterwards in order to add the synthetic Luminance to the RGB frame.

Some people argue that there's no need to take luminance frames if you have a synthetic Luminance.
Do you agree with this assumption?

Thank you

Konstantinos

[Octane]

Use the SubFrameSelector script to find the image with the best FWHM and lowest eccentricity and note it down.

Next, StarAlignment and use the image from above as the reference registration image.

Next, ImageIntegration to combine all the calibrated and registered RGB frames into your new synthetic luminance.

H

[konstantinos75]

Hi

I have found these three methods which describe how to make a synthetic L in Pixinsight.

I need to experiment now.


synthetic luminance method 1
===============================

R frames stack -> master R frame
G frames stack -> master G frame
B frames stack -> master B frame

Align R,G,B frames

ImageIntegration tool
- Combination = Average
- Normalization = additive with scaling
- Weights = Noise evaluation
- Scale estimator = iterative k-sigma
- Generate integrated image = enabled
- Evaluate noise = enabled
- Pixel rejection = No rejection
- Clip low range = disabled
- Clip high range = disabled



synthetic luminance method 2
===============================

R frames stack -> master R frame
G frames stack -> master G frame
B frames stack -> master B frame

Align R,G,B frames

pixel math: master R+master G+master B



synthetic luminance method 3
=============================
synL1 = ImageIntegration( red1 green1 blue1 )
synL2 = ImageIntegration( red2 green2 blue2 )
...
synLn = ImageIntegration( red(n) green(n) blue(n) )

finalLuminance = WinsorizedSigmaClipping ( L1, L2...Ln, synL1, synL2..., synLn) // sigma =4, Normalization = scale zero offset

LRGB = LRGBCombinationTool ( finalLuminance/RGB) // L=0,5, Sat=0,38-4,5

[Octane]

Looks like you're going to have to experiment. :)

H

[Geoff45]

Quick and easy. I've done this a couple of times and it works really well. It's especially useful if your image is undersampled and you have too few images to drizzle separately in each filter. Just drizzle the lot and nominate the result as your luminance image.
Geoff

[lazjen]

That's very interesting Geoff. I hadn't thought of that approach. Let me see if I've got this right for the situation where you may not have enough images in each filter to drizzle.

(H's steps a bit more expanded...)

Pick the best frame in SubFrameSelector across all filters.
StarAlign with all filter images, generate drizzle data.
ImageIntegrate/DrizzleIntegrate with all to generate luminance.
So then it should be possible to use the drizzle files for each filter to make drizzled image for each channel for an eventual recombine (e.g. LRGB?)

[Geoff45]

Hi Chris. What I did was to create the synthetic luminance by drizzling everything. Then i just used straight ImageIntegration separately on the registered R, G and B files. I didn't drizzle these stacks. Then combine to get an RBB image (no drizzle). Combine this with the drizzled synthetic L via LRGBCombine. The fine detail in the luminance comes through. Think of it as a bit like using binned colour with unbinned luminance.