Drizzle and Dynamic Crop in PixInsight 1.8.5

[Igor]

Hello,

How do you proceed to drizzle images after a Dynamic Crop in PixInsight 1.8.5 ? When you crop a set of images in order to delete black edges and borders, you lose the drizzle information because your files changed (croped files).

In PixInsight 1.8.4 it was not really an issue because you can use ROI in ImageIntegration in order to avoid to croping images but in PixInsight 1.8.5 you can not do that anymore 

Does anybody have an idea or the correct procedure to drizzle images after a Dynamic Crop ?

Thanks a lot

[RichInLesta]

I think the way you posed the question is confusing.  The first line suggests you're trying to crop images AFTER drizzling.  And  your third sentence asks about applying drizzle AFTER cropping.

I actually always crop at the very beginning of my workflow, so I've never run into a situation such as (I assume) you're asking about.

[Igor]

I cropped the images after registering in order to detect the black edges. However, drizzle files were generated in StarAlignment, i.e. before to be cropped. So I lose the drizzle reference after croping...

[drmikevt]

Igor

Obviously, you can not do what you are doing.  Do this instead:
 - Choose a reference image and run Image Integration on your images using Linear fit rejection
 - Use the resulting slope, dark and light rejection maps to create your crop.  I start with the slope - apply Dynamic crop to it, adjust the sides and then save an instance to the work area (drag the triangle to a blank space on the work area).  Apply that new instance to each reference frame and make sure the bad areas are cropped.  Apply it to the integration frame and make sure it looks like you want, including rotation. 
 - When it is how you want, apply your crop - your image should be in it's final configuration - and rename that image 'registration_ref' or something.
 - Use that image to register all your images, including the ones you used to make the image.  This will crop, rotate and register your images all in one step. 
 - Now, you can integrate and drizzle as you like.

Good luck!
Mike

[Igor]

Hello Mike,

Thanks a lot for your support. I guess that I did something wrong with the drizzle procedure before. Now I will follow your advices.

When you do "Choose a reference image and run Image Integration on your images using Linear fit rejection". Before to do that I guess that you must proceed to a first registering of the images  (StarAlignment process) ?

Regards

Igor

[drmikevt]

Yes, it is assumed that you have registered before running Image Integration. 

You don't *have* to use Linear fit - I just like it because sometime the 'slope' rejection frame makes it easier to see what needs to be cropped. 

And - it is important to note that you can not move images/files around once you start the registration process.  Leave everything in place until you finish your final drizzle image.

And - the above process is not mine, it is recommended by David Ault and you can read about it in more detail here:  http://trappedphotons.com/blog/?p=693.  He does not cover drizzle, but you would just add it to the end of his tutorial. 

[Igor]

Thanks again Mike. I fully understand now how it properly works.

In order to easily localized the black edges I usually do an ImageIntegration of all my images with "Minimum", "No Normalization", "No rejection" paramaters. But the slope rejection frame is fine as well.

Regards