2.15
#...
·
 |
|---|
I stacked my M109 data using WBPP with 2x drizzle, processed the data and then saved the project. In the meantime I discovered that I may be wasting my time drizzling as I'm not under sampled unless the seeing is excellent. I also wasn't completely satisfied with my processing. So I went to process the non-drizzled master light from the stack. The image on the left is the 2x drizzle and the image on the right is the non-drizzled. These have had the same processes applied and in approximately the same way but the colour is completely different. In particular, I can't get any of the magenta Ha regions in the non-drizzled data. How can this be? It's exactly the same data from the same stick, the only difference being the drizzle. |
3.31
#...
·
·
4
likes
|
|---|
|
My opinion is that, on the drizzled image, the star removal process managed to extract the stars better and preserve the Ha regions. On the non-drizzled image star removal removed both the stars and the Ha regions (probably because with half the resolution they become small and look like stars). Regarding colors, if you use some kind of photometric color calibration, they obviously rely on stars and drizzle (as written on PixInsight documentation) is the only way to preserve photometry with OSC, and the calibration process may give different results. In addition if you don't need drizzling 2x the resolution, you could just drizzle 1x or resample by 50% the final image. Daniele |
1.91
#...
·
|
|---|
|
Are the 2 images processed and stretched in exactly the same way at each step? I did lots of drizzling on a project during the fall and winter. It was not my experience that it changed my colors, but maybe the overall improvement in resolution that drizzling helps with might, in your case, have the effect that you can better get the colors to show better. |
3.61
#...
·
·
6
likes
|
|---|
|
I see that you use a OSC camera. In your case, I think you should always use the CFA Drizzle (at 1x, you you are properly sampled, or 2x, if you are undersampled). CFA drizzle on proper OSC color data means that PI reconstructs the color data using a drizzle algorithm instead of the CFA debayer. Debayering introduces less color fidelity than CFA Drizzle (which, according to some experts, can even recover the color fidelity close to what you would get when shooting mono, though it is a somewhat controversial and heated topic). There are several threads on this subject here and on CloudyNights on the subject. So answering your question, I think it is very well possible that you CFA Drizzled image may have more color fidelity than the one where color was constructed by debayering. |
0.00
#...
·
·
1
like
|
|---|
| I totally agree with what Pedro A. Sampaio wrote |
|
2.15
#...
·
·
1
like
|
|---|
Thanks for everyone's help.Daniele Borsari: That's a good point. I'm not sure that I masked the galaxy before removing the stars. I'll have a look into this after work and report back. Thanks for the info. Pedro A. Sampaio: That's very insightful, thanks so much. I just thought that drizzling was only used to combat under sampling and to increase the pixel size of the image. This is new to me so I'll re-stack with a 1x drizzle applied and report back. Is this all I need to do (Screenshot attached)?  |
|
2.15
#...
·
|
|---|
|
Just to update this, I've over-stretched the stars image to see if StarX took some of the galaxy with it and I can't find any evidence of that. I did however, re-stack the data using 1x drizzle and can confirm that there was indeed much better colour. Thanks so much for the help, that's something new I've learned. |
