LocalNormalization on Light Frames without Flats

Zak’s Astrophotography

Hi Adam,

I am wondering if it is possible to use LocalNormalization on images that don't have flat frames, and if so, how would you go about doing so?

I have been using it with it's default parameters in WBPP as I am currently going through and re-processing old data where I did not take flat frames with the new GradientCorrection tool. I have noticed that the results are mixed depending on how bad the gradients are, which are more prevalent on images with dust spots and odd edges. 

I am also aware that the PixInsight developers are currently working on the next iteration of GradientCorrection, which was supposed to release last week. It does look promising, but I will see how it performs once it is released.

Zak :)

BlockHead

Hi Zak,

There are some confusing sentences in the above.

To answer your question directly- yes, you can use LN on data that is calibrated without flats. 

If you image have vignetting, for example, then LN will faithfully match the LN reference vignette to all other frames and rejection will continue to work properly. However, LN will not in any way change the uncorrected non-uniformity (gradient) in your data.

You can subsequently use gradient removal tools on the masterlight you generate as normal. However, as an aside, the correction of this gradient is MULTIPLICATIVE and NOT strictly additive. GradientCorrection, even in its new form, will not properly correct for multiplicative gradients. This means in general you need to correct your data with flats in order to use the new GradientCorrection tool.

DBE does have the capability to remove multiplicative gradients (division) and additive ones (subtraction). But how to do this is out of scope. 

So in your statement "I did not take flat frames with the new GradientCorrection tool..." confused me. 

I hope this helps and you will take my considerations into account.

-the Blockhead

Zak’s Astrophotography

Thanks for clarifying Adam, really appreciate it! Sorry about the confusion with my sentences, upon looking back, I have definitely mucked up my wording.

Good to know about GradientCorrection and it's limitations on correcting images without flat frames. What I was meaning to say is "I have been using GradientCorrection on my images without flat frames with mixed results."

I will have to try and find ways with DBE on how to best correct the gradients in my images without flat frames. I am not sure about the other software that uses "AI" will correct these gradients, although from my experience using it has been mixed as it can nuke nebulosity in nebula-rich images. Seems like it will be a trial and error process to best correct these pesky gradients!

Zak :)