Background extraction: am I doing it wrong?

Software Siril
1

I’m getting considerable background gradient in my recent images of exactly the kind that I thought the new RBF background extraction was supposed to take care of. (See the upper right on this image of M51.)

I’d be interested in any suggestions more Siril users more sophisticated than me (pretty much everyone on this forum) might have.

Thanks

2

Hello,

It is impossible to say something from a pdf screenshot of a jpg image. To really say something about your issue we need original data.

3

Here’s the stacked FITS image before I do anything else to it: M51_filtered.fit.

My normal workflow when I get to this point would be crop, background extraction, photometric color calibration, histogram transformation and remove green noise.

Thanks!

4

It is difficult to obtain something better than:

image
image1210×808 461 KB

This image suffers from different problems.

  • flats are not removed properly
  • there is a remaining artifact (circular bands) coming from registration I guess. Try using the nearest neighbor algorithm
5

Thanks for taking a look at this! I’m not sure I understand what you mean by “flats are not removed properly”. I’m using a somewhat modified script to generate the FITS file, and I have pre-stacked bias and flat files (bias_stacked.fit and pp_flat_stack.fit) in my process folder that get applied I think at the right point. Is is just that the quality of my flat file is bad?

############################################
#
# Script for Siril 1.0
# July 2020
# (C) Cyril Richard
# Preprocessing v1.0
#
########### PREPROCESSING SCRIPT ###########
#
# Script for color camera preprocessing
#
# Needs 4 sets of RAW images in the working
# directory, within 4 directories:
#   biases/
#   flats/
#   darks/
#   lights/
#
############################################

requires 0.99.4

# Convert Dark Frames to .fit files
cd darks
convert dark -out=../process
cd ../process

# Stack Dark Frames to dark_stacked.fit
stack dark rej 3 3 -nonorm
cd ..

# Convert Light Frames to .fit files
cd lights
convert light -out=../process
cd ../process

# Pre-process Light Frames
preprocess light -dark=dark_stacked -flat=pp_flat_stacked -cfa -equalize_cfa -debayer

# Align lights
register pp_light

# Stack calibrated lights to M51_filtered.fit
stack r_pp_light rej 3 3 -norm=addscale -output_norm -filter-fwhm=80% -filter-round=80% -out=../M51_filtered

cd ..
close
6

Hi, I was trying to share my pre-stacked flats FITS file so you can take a look and maybe comment on what I’m doing wrong, but discuss.pixls.us interpreted that as I was spamming/trying to sell something. I can email the file to you if you prefer.

7

Hello, visibly the flats do not match the light images, have they been taken with the same filter and without moving or changing the optical train? If they are old maybe it’s a question of dew or dust moving on some surface.

8

@ple Welcome to the forum! You are encountering a safety feature placed on new members to prevent spam/bots. After several more posts, you should be okay to share images and files.