PixInsight - Finalizing the Image

Histogram Stretch

updated: 2025-10-04


Purpose

Performing a full stretch on linear images

Activation

Menu: Process 🡺 All Processes 🡺 HistogramTransformation

Process Explorer: IntensityTransformations 🡺 ScreenTransferFunction

Input
  • Final still linear image from sub folder "Work"
  • Plus masked image from previous step with protected foreground (if available)

Output

Stretched image, file name postfix: “*_HT” into sub folder "Work"

Previous Step

Next Step

Tutorial

Stretching an image with Histrogram Transformation in Pixinsight (youtube.com)


Step

Action

Description

1

Open the color calibrated image and unstretch it

(20221029-233853_M33_ZWOASI294_0002_SPCC_NXBX.xisf in this example)

🡺 🡺

2

Open Histogram Transformation (HT)

and reset the function

3

Select the current image and unstretch it

4

Enable Real Time Preview


5

Set inital stretch

To set an initial strech you can 

  • drag the midtone slider (the gray triangle 1 in the middle under the histogram) to the left ou can until a clearly visible image appears or until it reaches the right-hand sloping edge of the histogram
  • and then the shadows slider (the gray triangle 2 on the left under the histogram) to the right until you see a acceptable image


OR


  • click on the Autozero shadows button ( 3 )
  • and the Autoclip highlights button ( 4 )

6

Resulting Preview:

(Only a image section is shown here)


Apply the settings
You can either:

  • Click on the blue square 
  • press F5 
  • or drag the blue triangle onto your image

to transfer the settings to your image.

6

Reset HT

to reduce the double stretch in the preview window

  

7

Drag the left slider 2 to the right 
until until it reaches the left-hand rising edge of the histogram


and the slider 1 to the left again

until it reaches the right-hand sloping edge of the histogram

8

Resulting Image

(Only a image section is shown here)

9

Apply the settings
You can either:

  • Click on the blue square 
  • press F5 
  • or drag the blue triangle onto your image

to transfer the settings to your image.



10

Repeat the steps 5 through 9 again

until you are happy with the result.




  

11

Close the Realtime Preview Window

and reset HT


12

Close HistogramTransform


13

Save the fully stretched image

file name like “*_HT.xisf” or similar into sub folder "work"

15

Optional: Export the final image to JPEG format

file name like “*_HT.jpg” or similar into sub folder "work"


Created with the Personal Edition of HelpNDoc: 5 Reasons Why a Help Authoring Tool is Better than Microsoft Word for Documentation