PixInsight

Creating a Mask

updated: 2024-03-17


Purpose

Masking foreground and background objects

Activation

Menu: Image 🡺 Extract 🡺 Lightness (CIE L*)  

or

Tutorial

https://www.youtube.com/watch?v=JtA4UoaAAas  (Part 6  DBE - starts around timestamp 2m56s)


Step

Description

 Action

1

Open the last Image

 File like “*_i_c_DBE_BN_CC_HT.xisf”

2

Click on the Lightness (CIE L*) Icon

The luminance will be extracted from the image and a B/W image be created.

  🡺

3

Unstretch the b/w Lightness image

or reset the STF (applies only to not fully stretched images!)

4

Open the ScreenTransferFunction (STF)



5

Open HistogramTransformation

and select the b/w lightness image as target image (has an "_L" trailer)

6

Do a Autostretch in STF

on the unstretched lightness image

.  🡺

7

Send STF Values to the HistogramTransformation

drag the little blue triangle of the STF to the bottom of the HistogramTransformation


The HistogramTransformation will now show the histogram of the b/w image.

               SFT                                                                         HistogramTransformation

8

Send HistogramTransformation Parameters to the B/W Image

Drag the little blue triangle from the HistogramTransfprmation onto the B/W image, this will turn completely white.

 🡺

9

Reset the STF

to show the stretched image again - notice that the green bar at the left handle is gone meaning that this image is now stretched.

  🡺

10

Close the HistogramTransformation

no longer needed


11

Apply the Mask to the Original Image

Pull the tab of the B/W stretched image right below the tab of the original image to apply the mask


The red image is the MASK which will be used further. Notice the tab on the left side of the windows turned to brown indicating a mask. 


Everything in red is protected (here this is the background). By inverting the mask you can also protect the foreground which is good if you want to reduce noise on the background.


You can use the following function from the menu to alter the mask:

 🡺

12

Hide the Mask

Make sure the foreground is protected before you hide the mask.


After hiding the mask, the mask is still there (as you can see from the brown tab at the left side of the image)

or Ctrl+K

13

Continue with any next step

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