Flat Darks prep and use in PI [Deep Sky] Processing techniques · Jeff Bennett · ... · 12 · 212 · 0

Recently, I switched from the ASI 2600MC to the ASI2600 MM Pro with LRGB filter wheel.  It's been a complicated journey for sure.  Im trying to figure out dust motes, flats etc and was really stumped.  I often find numerous dust motes in my my linear images, even after I integrate flats.  I use PI to get rid of them, but I always believed once you incorporated flats, the dust motes would disappear.  They don't.  So I went on a search of processing suggestions.  For the first time, I used AI, GROK (Musk creation) to help me.  Here is what I discovered and I am sharing this information with you for suggestions and comments.  Clear skies.

To create flat darks in PixInsight's Weighted Batch Preprocessing (WBPP) script, follow these steps:

1. **Understand Flat Darks**: Flat darks are calibration frames that match the exposure time, gain, offset, and temperature of your flat frames. They are used to correct noise in flat frames, which are typically short exposures (e.g., 1–5 seconds) taken to correct for vignetting and dust on the sensor.

2. **Capture Flat Darks**:
   - Take dark frames with the same settings (exposure time, gain, offset, and temperature) as your flat frames.
   - Cover the telescope or camera to block all light, ensuring true dark frames.
   - Capture enough flat darks (typically 20–50) to ensure good signal-to-noise ratio.

3. **Prepare for WBPP**:
   - Organize your files in a folder structure. For example:
     ```
     /Data
       /Lights
       /Flats
       /Darks
       /FlatDarks
       /Bias
     ```
   - Ensure flat darks are in their own folder or clearly named (e.g., `FlatDark_1s.ISO800.fit`).

4. **Run WBPP in PixInsight**:
   - Open PixInsight and launch the WBPP script (`Scripts` > `Batch Processing` > `Weighted Batch Preprocessing`).
   - **Add Files**:
     - Click the “Add Files” button and load your light, flat, dark, flat dark, and bias frames.
     - Alternatively, use “Add Folder” to automatically load files from organized folders.
   - **File Grouping**:
     - WBPP automatically groups files based on metadata (e.g., exposure time, filter, gain).
     - Ensure flat darks are recognized as matching the exposure time of your flats. If not, manually assign them:
       - In the “Calibration” tab, select the flat dark frames and link them to the corresponding flat frames.
   - **Calibration Settings**:
     - In the “Calibration” tab, ensure “Use master flat dark” is checked if you’re using a pre-integrated master flat dark.
     - If you’re using individual flat darks, WBPP will integrate them during processing.
     - Verify that flats are calibrated with flat darks (not regular darks) in the calibration diagram (click “Show Calibration Diagram”).
   - **Output Settings**:
     - Choose an output directory for processed files.
     - Optionally, enable “Generate master flats” and “Generate master darks” to create master calibration files.
   - **Run WBPP**:
     - Click “Run” to start the preprocessing. WBPP will calibrate flats using flat darks, then use the calibrated flats to process light frames.

5. **Verify Results**:
   - Check the output folder for the master flat dark and calibrated flats.
   - Inspect the log file (`log.txt` in the output folder) to confirm flat darks were applied correctly.
   - If issues arise (e.g., mismatched exposures), adjust file assignments or recapture flat darks with correct settings.

6. **Tips**:
   - **Naming**: Use descriptive file names or metadata to help WBPP identify flat darks (e.g., include exposure time or “FlatDark” in the filename).
   - **Master Flat Dark**: If you have a library of flat darks, pre-integrate them into a master flat dark using PixInsight’s ImageIntegration process, then load the master into WBPP.
   - **Exposure Matching**: Flat darks must match the flat exposure time exactly. If your flats vary (e.g., 1s, 2s), take corresponding flat darks for each exposure.

If you encounter issues, let me know specific details (e.g., error messages, file types), and I can troubleshoot further!

him, "- In PixInsight, I’ll load all the files into WBPP and the only linking I have to do is the FLATS to the LIGHTS!! I’ve found PixInsight automatically links all the darks to all corresponding frames based on filter and exposure time ….. DARKS to LIGHTS ….. DARKS to FLATS". 

I didn't know that, Ill try it, thanks

Sam, Im having difficulty with Flat Darks.  I have made dark frames for each LRGB Flat frame (same temp, focus, Time etc).  Are Flat Darks darks and for calibration belong in the Dark category?  When I put mine there, they all show (.6 sec, .083 sec, etc per filter) but under darks in calibration I only see one .21 sec dark in addition to standard darks for 60 second and 120 second exposures.  Do I have to add the Flat Darks using " Add Custom" ??  Im confused you can tell.  I didn't have any of these issues with a MC CMOS.  Also I finally found the "Chart" to map the integration.  Looks like not all darks (Flat Darks are not showing.  Any suggestions?  Yes, I asked Grok several of these issues and I have answers for each (I'll provide if you like), but sometimes asking someone with similar interests is much better.  Thanks for your patience.

"exposure tolerances". ?? Where do I find that?

Jeff Bennett:
"exposure tolerances". ?? Where do I find that?

*Jeff, 2 things 

- exposure tolerances for darks is in the darks tab!! Click on the darks tab along the top of the window then in the middle panel above the rejection parameters you’ll find exposure tolerances and a slider for threshold, leave the slider as it is but change the tolerance number to 0 or 1!! That should separate and group all darks into their own sub groups based on exposure time 

- flat darks are purely a dark frame for a corresponding flat!! To add them in PI, use the add darks button!! The name is confusing but they’re a run of the mill dark frame, so add them into PI the sane way you would for other darks

Thank you, it must be the flats then.  They seems to be added to the integration instead of subtracted from the lights.r

Thank you John.  Im working through the issues now.  I have permanent setup in my observatory, so dust isn't or least should be a huge issue.  I shooting new darks tonight at temperature (-10).  Tomorrow night I'll shoot a series of flats (LRGB).  I used SGP Flats Wizard to calculate the exposure time for each filter.  Hopefully it will succeed .  Thank you again.  Jeff