Starguide - A Practical Guide to Astro-Photography

PixInsight - Noise Reduction

updated: 2021-08-24

Purpose

Is used to reduce noise on the image background

Activation

Menu: Image 🡺 Extract 🡺 MultiscaleLinearTransform

Process Explorer: NoiseReduction 🡺 MultiscaleLinearTransform

Input

Corrected image, file name “*_i_c_DBE_BN_CC_HT.xisf” or similar into sub folder "aligned"

Plus masked image from previous step with protected foreground

Output

Corrected image, file name “*_i_c_DBE_BN_CC_HT_MLT.xisf” or similar into sub folder "aligned"

Previous Step

Creating a Mask

Next Step

Full Final Stretch

Tutorial

(458) Pixinsight Part 8 noise reduction and Full stretch... - YouTube  (Part 8  Noise Reduction and Full Stretch starts around timestamp 7m32s)

Step

Description

 Action

1

Create a Mask

see > Create a mask

2

Invert the mask to work on the background noise

so that the background is unprotected

and the foreground is protected

and hide the mask with CTRL+K

3

Open Multiscale Linear Transform

4

Open a Preview Window

depending on the objects in you image you might include nebulae, galaxies or stars

Press ALT+N and draw a rectangle on your masked image

5

Open a Real-Time Preview Windows

and select as source the preview from the previous step

6

Set Dynamic Range Target

Select Luminance

7

Set Noise Reduction Parameters Layer 1

Try followings settings for layer 1:

Bias: 0.0

Threshold: 3.0

Amount: 0.3

Iterations: 3

You can immediately check the impact by toggling the before / after icon on the preview window:

After:    

Before:

8

Set Noise Reduction Parameters Layer 2

Try followings settings for layer 2:

Bias: 0.0

Threshold: 2.0

Amount: 0.3

Iterations: 1

9

Set Noise Reduction Parameters Layer 3

Try followings settings for layer 3:

Bias: 0.0

Threshold: 1.0

Amount: 0.3

Iterations: 1

Before:

After:    

10

k-Sigma Noise Thresholding

Experiment with threshold and amount, soft threshold and multiresolution. 

11

Close the Preview Window

12

Apply the function to your full Image

Pull the little blue triangle onto your image

before                                         after
 

13

Reset the Multiscale Linear Transformation

This will clear all previous settings

14

Switch to Chrominance in the Dynamic Range Extension

and extend the function to 7 layers

15

Change the Preview from Step 2

and select a section with background and some stars to see the effects

16

Open the Real-Time Preview Windows

select the preview from step 2

17

Set Noise Reduction Parameters 
for Layers 1 to 4 

Layer 1:

18

Close the Real-Time Preview Window

19

Apply the Function to Your Image

Pull the little blue triangle onto your image

20

Close Multiscale Linear Transform

21

Remove the Preview01

22

Remove Mask

... and the brown color on the window tab returns to black

Menu 🡺  Mask 🡺  Remove Mask

23

Close the B/W Luminance window

24

Save the Result

Append a "*_MLT" to the file name

file name “*_i_c_DBE_BN_CC_HT_MLT.xisf” or similar into sub folder "aligned"

25

Keep open image for the next step

• Full Final Stretch

it will be reused in the next step.