BXT AI4 Not Reducing Smaller Star Sizes

Zak’s Astrophotography

Hi Adam,

I have been playing around with BXT AI4 with great results so far, but I have been trying to follow along with your newest Fundamental Workflow of NCG 1491, specifically the part where you use BXT to significantly reduce smaller star sizes to emphasize the nebula more, but I'm trying to do it with my own images that have lots of smaller stars. I've tried using both MMT and MLT (with the same methods in your video) to produce bright star masks, but when I try to apply the inverted mask to the big stars, it hardly protects thems, and even without the mask, I've tried applying BXT globally to the image but the stars are not being reduced to the extent they do as shown in your workflow video.

For reference, I am using significantly undersampled data according to the Astronomy Tools CCD Suitability calculator. Would this be the reason for why the stars aren't being reduced a lot? Maybe my expectations are too high for BXT AI4, but I did use Correct Only first before SPCC, and that is where I noticed the most improvement in terms of star size reduction.

If you need me to provide any files for some of my images, please let me know.

Thanks Adam,

Zak

BlockHead

Well, yes, if the stars are already 1 or 2 pixels in size there isn't anything more that BXT can do. Then you can just rely on the other methods such as the MTF adjustment (Bill Blanshan) or even my "older" method. 

Concerning the mask, did you by chance create the mask using MMT/MLT with linear data? The result will be a linear image! You need to permanently stretch the mask in order to have it be near 1 values (white) or near 0 values (black). You probably were using a linear version of the image which indeed would not work.

-the Blockhead 

Zak’s Astrophotography

That's what I thought, thanks for clarifying Adam. I went back and tried it on my image of M20, and sure enough, it worked!

You are right, I kept on forgetting to stretch the mask first then apply it to the image. I was perplexed as to why it wasn't working, but I went back and watched your video again and you indeed stretched the mask which I must have somehow missed. I use both MMT and MLT depending on which one looks better to me.

Also apologies in my delayed response. We were away for most of the Christmas/New Year's period and had limited access to internet and only got back a couple of days ago.

Zak :)