Nsg with drizzlex2 poor result

MAURIZIO MOLLICA

Dear Adam,

in order to deal with (incoming) under-sampled data (recently I purchased a focal reducer, f/3.9,for my Askar Fra 400 been used with asi 2600 Mc color with 3.76 micron pixel) I started to go deep in understanding drizzling.

My goal was not to loose NSG process with drizzle data and I got it (Instrtuction are very clear on how to do it).

The question rises straight from the result I get.

I have two results:  A) Nsg integration with no drizzle

B) Nsg integration with drizzle 2x.   (n° 67 dithered imgs, 0.70 drop shrink).

There is a big difference (to my eyes) between the two images:

 image A  appear to have much more contrast and higher S/N (the already weak IFN is almost non-existent in image B!).

The other aspect that struck me is that the two images also have a completely different gradient pattern despite they have been generated from the 

same Nsg process: this look really odd to me!

I would really appreciate your thoughts on this aspect!

Just for reference I am sending you the two images attached to this (in jpeg format) .

If you would like me to send you the huge xisf file, just let me know!

Thanks in advance,

Maurizio Mollica - Italy

BlockHead

You perfomed CFA drizzle correct?

I don't want to assume anything. 

-The Blockhead

MAURIZIO MOLLICA

Hi Adam,

Yes, I am "fairly" sure, I mean, I followed the path...

Path:

1) Wbpp perform calibration and registration with drizzle option enabled (it actually asks you to do 

integration too);

2) In the NSG process I load the appropriate files (registrered), selecting "drizzle data" and 

"normalization data"  in the Output section (no error messages occurred, obviously I own NSGXnml 

module);

3) Once the job is done, NSG correctly opens the "Integration" and "Drizzle Integration" processes;

4) Obviously I started the processes in the order I wrote them, that's it!

So, this is the path I follow, did I miss anything?

Thank's,

Maurizio

BlockHead

Well... with respect to NSG... you  did regular integration. But did you do #4 Drizzle Integration with CFA Drizzle?

-the Blockhead

MAURIZIO MOLLICA

Yes, sure!

I send you my settings,

Maurizio

BlockHead

Looks correct.

The images will certainly be different. The right way to compare the is to do the CFA drizzle without upsampling. The reason they look different is that the integration without drizzle is interpolating wrong colored pixels (mixing colors)- whereas the CFA drizzle does it correctly. This is the entire point of doing the CFA drizzle (even without upsampling). Examples that show your observations and the differences you see are reproduced in the SPCC documentation. Scroll down near the bottom with the example images.

-the Blockhead

MAURIZIO MOLLICA

Ok. Many thanks Adam!