Some questions for creating a mosaic

Hi David @dav78,

Great and promising mosaic that you are working on here 😉

Each panel has been calibrated and integrated with Pixinsight (I'm waiting for the 1.072 )

No problem, do let me know, how processing in APP 1.072 works now with your Sony ARW data 😉

In repsonse to your questions:

- does gradient/LP have to be removed in each panel before creating the mosaic, or after creating the mosaic, or both ?

In most cases, I get the best results if I perform it after the creation of the mosaic. If you do it before, then you need to be very carefull. If the correction is not good, then the final result could be worse is my experience. It does depend a lot on the data and from the looks of it, I think you would get the best and most robut result by performing it after the creation of the mosaic.

- is it possible to avoid distortion of the edge panels (see the gif after) ?

Yes, I can only assume that you refer to the stretching of the left panels? That is projective distortion due to using the projective registration model and the default rectilinear projection.There are 2 ways to reduce this.

1. choose a reference before registration manually, choose the mosaic panel in the center to get the least projective distortion on the edge of the field of view.
2. use the calibrated registration model and then project your data with the equirectangular projection instead of the default rectilinear projection.

Combine both for the least distortion 😉

The projection distortion is normal to appear in a mosaic with short focal lenghts. Rectilinear projection only works for field of views smaller than 120 degrees.

- what is the best setting to use ? I've tried advanced and normal mode, with for both MMB 15, 1st LNC it 3 or 2nd LNC it6. From the result shown in the gif below, which one should be chosen ?

My impression is that the advanced normalization mode with 1st degree LNC is the best here. What do you think? Were these corrected with the Light Pollution Correction tool as well?

Kind regards,

Mabula

Hi Mabula,

Thank you for yours answers.

I will try that and post the result, as soon as I'll have time 😉 it's quite long to process a 90 mpx mosaic.

Yes, advanced mode with 1st degree LNC and 3it seems to give the best results. Let's see if the result is the same when the gradient is removed after integration of the mosaic.

The 1.072 is finally out, that's great 😉 thanks for your work.

Unfortunately i have some error messages, I'll make a post for that.

Hi @mabula-admin,

I've made some more tests.

Panels stretching :

Has advised, I used the calibrated registration model with equirectangular projection, and the panels are almost not stretched anymore, that's great! But the are misalignment of some stars: in the lower middle left and in the upper middle right. I tried with more 3000 stars in star detection, same result.

Gradient :

I tried to create the mosaic before removing gradients : I think the resulting picture is creating a general gradient that doesn't match with the different gradient in each panel, so the result is odd... and it's very difficult to get good color calibration.

In the following pictures : result of the mosaic without gradient removal and calibrated registration model, and details of stars misalignment areas.

Hi @mabula-admin

I finally found the good settings for creating mosaic, with my data/gear at least 😉 : gradient removal for each panel, star detection at 3000, calibrated registration model with equirectangular projection, DDC checked but same lens and camera have to be unchecked to get good panel alignment, 1st degree LNC and 3 it, multi band blanding at 15-20.

That's great!

Processing was made in Pix : processing of such mosaic isn't possible in APP with my computer, to much slow, and I needed a masking tool.

Here is the picture, at 33%

That is a fabulous image!!! Please submit is for APOD! I am serious!

Wouter

It indeed is fabulous, fully agree.

Thank you @wvreeven and @vincent-mod

It was a tough work, and I'm satisfied with this result, especially considering my sky this winter. And APP is a great help for gradient removal and mosaic merging (thanx @mabula-admin for this).

Submitting for APOD, why not. But the way they choose the pictures is a quite strange sometimes, but yes, I will 😉