The Image processing settings appear in the Image processing menu entry of the Phoranso menu bar and are used during the Calibrate files operation. We strongly recommend to first read the Calibration pipeline section of the User Guide.


  1. In step 3 of that section, we talk about tolerance settings. You enter the tolerance values through the Image processing settings menu:



  1. It allows to set the Max temperature difference (tolerance) and the Max Exposure duration difference to consider master frames to be matching with a Science image. Entering a value of 0 will reject any tolerance, i.e. only perfect matches are accepted. Entering a value of -1 will accept any tolerance. 

    Let's illustrate with an example. In the process of calibrating a science image, Phoranso subtracts the master dark frame from the science image to remove the dark current noise. When the master dark frame was captured under different exposure time or temperature conditions, it might not accurately represent the noise in the science image. We have to distinguish between several possibilities:

Exact matching (no scaling)


    • If the user opts not to work with scaled master dark frames, Phoranso will exclusively accept master dark frames that precisely match the exposure time and temperature conditions of the science image. 
    • In the absence of a matching frame in the Calibration group, the dark current noise correction will be omitted.

Tolerance matching (no scaling)


    • In scenarios where the user chooses not to work with scaled master dark frames but allows for a certain tolerance in temperature and expousre duration, Phoranso will accept a master dark frame if the difference in temperature and exposure time falls within the specified tolerance. 
    • If no suitable frame is found within the specified tolerance range, the dark current noise correction will be omitted. 

Scaling 


    • If the user selects the option Scale Master Dark image during calibration in the Calibrate files operation, Phoranso will adjust the 'nearest' master dark frame from the Calibration group to match the exposure time and temperature conditions of the science image.