Starguide - A Practical Guide to Astro-Photography

PixInsight - Image Post Processing

HDR Multiscale Transform

updated: 2021-10-28

Purpose

HDR Multiscale Transform - produces an enhanced image

Activation

Menu: Process 🡺 All Processes 🡺 HDRMultiscaleTransform

Process Explorer: Wavelets 🡺 HDRMultiscaleTransform

Input

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

Output

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

Previous Step

• Full Final Stretch or any image form chapter Improving the Image

Next Step

• LocalHistogramEqualization

Tutorial

https://www.youtube.com/watch?v=MhaW1mcybzk  (Part 9  HDR)

Step

Description

Action

1

Open the Latest Image

from the last processing step

e.g.  “*_SM.xisf”

2

Create a Luminance Mask

this will create a B/W luminance image.

Drag the tab on the left side of the luminance image on the left of the light frame image to create the mask. 

Then hide the mask (CTRL+K)

3

Make a Preview

of a region of interest in your image

and to reduce processing time during the testing

ALT+N

4

Open HDRMultiscaleTransform

Play around with the parameters, with the given image these parameters gave a very good result:

Number if Layers: should be set between 4 and 6, lower and higher values will usually return a degradation of the image

Number of iterations: a higher value will soften the image, the often best value is 1.

Deringing: are designed to removed artifacts around sharp edges like stars - try is, result depend on the original image

Midtones Balance: either automatic or manually set to 0.1

5

Apply the function to the preview window

Pull the blue triangle at the lower left corner onto you preview picture, that starts the process. This can be repeated each time you change the HDR function parameters.

6

Compare Original and Transformed Image

in the preview window

Example: using the B3 Spline scaling function

7

Compare Original and Transformed Image

in the preview window

Example: using the Gaussian (11) scaling function .

The Gaussian (11) scaling function showed even better results, clearer structures in the nebula and more stars where left over

8

Apply the HD function

Pull the blue triangle at the lower left corner onto you main picture, that starts the process.

9

Remove the Preview and the Mask

Menu 🡺  Mask 🡺  Remove Mask

10

Close the HDR tool

11

Final Step

file name like  “*_i_c_DBE_ABE_BN_CC_ HT_MLT_FS_SM_HDR.xisf”

or "20170921_M8_FUJXT1_i_c_DBE_ABE_BN_CC_ HT_MLT_FS_SCNR_SM_HDR.xisf" in this case

using postfix _HDR

file name like  “*_HDR.xisf”