PixInsight - Color Correction

PCC - Photometric Color Calibration

 

updated: 2024-07-30


Purpose

PhotometricColorCalibration: Calibrates the color of a linear deep-sky image based on documentary criteria.

The ColorCalibration tool performs a balancing of the colors of a linear RGB deep-sky image based on the following documentary criteria:

  • Maximize information representation in the calibrated color image.
  • Don't favor any particular color or spectral type as a white reference.

Note that this is a spectrum-agnostic color calibration procedure, very different from other methods based on fixing a white reference with respect to a particular spectral type.

Activation

Process > All Processes > ColorCalibration

Input

Backnoise neutralized image, file names like  “*_i_c_DBE_BN.xisf”, "*_i_c_ABE_BN" or "*_i_c_DBE_ABE_BN" from sub folder "aligned"

Output

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

Previous Step

Background Improvement

Next Step

Any topic under Color Correction

Ressources

Changes in PhotometricColorCalibration (PCC) | PixInsight Forum

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


WARNING: be careful if using a cropped image as the image parameters like focal length and pixel size acquired from the image may no longer fit and will probably result in a plate solver error! It's easier to use an uncropped version and crop later.

Notice: image solver capability has been removed from PCC. So before you can run the PCC process you either have to make sure you activated the Astrometry Solution in WBPP or run the Image Solver script (Script > Image Analysis > Image Solver) on the final master light image to update the master file with astrometric data.

Step

Action

Description

1

Calibration

The default average spiral galaxy reference is the best choice for deep space objects.

2

Catalog Search

PCC should always be used with local APASS DR10 or APASS DR9 databases in XPSD format, which can be downloaded from our Software Distribution interface. To avoid excessive breaking changes, we still support the possibility of accessing the APASS DR9 catalog via the online VizieR service. Still, this functionality is now deprecated and will be removed in a future version. When the Automatic catalog option is enabled in PCC, the process will use the best local APASS catalog available automatically through the APASS XPSD database server process.


Remarks: 

  • you must be logged into your PixInsight account to download the APASS databases!
  • Installing and activating the local XPSD database server

Using the regional online catalog:


Using a local APASS - XPSD database:

3

Signal Evaluation

4

Background Neutralization

  • The lower limit and upper limit parameters are now expressed in sigma units from the median of the background reference region, instead of literal pixel values. With this change, the background reference is sampled adaptively, solving several practical problems we have detected with previous versions. In practice, you rarely will need to change the default values of these parameters, and background neutralization will simply work in virtually all cases.
  • Best option is to create a preview window on a portion of the image with now stars or clouds and enable the Region of Interest option and get the coordinates from the the preview as shown on the right.

5

After Successful  Transformation

If successful you will see the calibration results:

6

Save the corrected image

into a file like *_i_c_DBE_BN_CC.xisf

(or 20170921_M8_FUJXT1_i_c_DBE_ABE_BN_CC.xisf in this case)

 









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