Problems while combining 1x1 L with 2x2 color data

[ManuelJ]

Hi,

I'm facing problems while combining data taken with 1x1 L (10 min subs), and 2x2 RGB at bin 2x2 (subs). I have some blooming in the brightest stars:

http://i52.tinypic.com/24cwth0.jpg

I think that the problem arises because there is more data in the 5 min 2x2 subs, so the stars are bigger in size. I have solved the problem with this equation, which perfectly extracts only the bloomed part of the stars from the RGB channels:

L = L
R = R-(R-L)
G = G-(G-L)
B = B-(B-L)

But this is not an elegant solution, why is this happening and how to solve it?. Shall I take shorter subs?

Regards,
Manuel.

[Juan Conejero]

Hola Manuel

From the crop you've posted I'd say you're trying to combine linear data. The LRGB combination process requires nonlinear (stretched) L and RGB images. We have recently released a 2-part video tutorial covering this subject:

http://pixinsight.com/videos/NGC1808LRGB-vperis/en.html

also available on YouTube:

http://www.youtube.com/user/PixInsight

If you haven't already watched these videos, I strongly recommend you do so. In this video Vicent shows an easy and effective way to achieve a good adaptation between luminance and chrominance, which is essential to perform an optimal LRGB combination, using the STF tool. Another method involves the use of the LinearFit tool. You can read a summary of this method in this thread.

Let me know if this helps.

[ManuelJ]

Yes, you've helped me a lot, thanks.