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Just come across an interesting watch, this guy uses huge samples, and only samples the outside of his image, kind of makes sense, I'll have to experiment to see for my self but he seems to get good results...

 

 

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Using larger samples is always preferable. 5 pixel as default, only gives you 25 pixels in each sample. Using 15 pixel size, gives you 225 pixels. Already a huge improvement. But, always look at the samples. Black pixels in a sample means that these are not taken into account for modeling. That's where the advice "don't use samples over stars" comes from. With larger samples, you can afford to lose pixels due to stars in your samples.

A few warnings re this video. 

The guy uses the same settings, regardless of image. Always let the image dictate which settings to use. Keep the model relaxation parameters as low as possible, but examine the samples. Avoid samples that have a colour bias (in colour images). 

Don't just blindly place samples. Put them where they are needed. In the video, samples are placed over the galaxy at top right. A sure way to ask for problems later on. To remove vignetting, it's better to place samples in each corner and a bit in along the diagonals (8 samples). Also a sample on each edge (+ 4 samples). Use division as correction method. To remove linear gradients, place a few samples along the path of the gradient. Always avoid areas of nebulosity (which he doesn't in the HH nebula). Use subtraction. If you have a combination, use the symmetry tools and set fewer samples. 

NEVER discard the background model without examining it. Not examining the model is plain bad practice.

 

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good points wimvb, i did notice that sample covering the galaxy at the top right and had to think about that lol, im still learning PI and im going through Rogelio's book at the moment, i find it interesting how different people process, its definatly a dark art thats for sure, i totally feel like a noob and ive only been doing AP for around 6 years, on and off lol

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4 minutes ago, tingting44 said:

im going through Rogelio's book at the moment

I would take Andreo's (or Adam Block's) advice over other's any time. Both are established astrophotographers who do this stuff for a living. And both have extended experience of Pixinsight and Photoshop. 

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10 minutes ago, wimvb said:

I would take Andreo's (or Adam Block's) advice over other's any time. Both are established astrophotographers who do this stuff for a living. And both have extended experience of Pixinsight and Photoshop. 

thats very interesting you would pick those over Rogelio, im loving this book right now, would you have a link to their advice if possible or if they have a book out id be interested, thanks :)

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1 hour ago, tingting44 said:

thats very interesting you would pick those over Rogelio,

His full name is Rogelio Bernal Andreo. We mean the same person. 😀

 

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1 minute ago, tingting44 said:

🤣 I'm an idiot 

Just confused, maybe.

Adam Block has a channel on youtube worth subscribing to. He also has a web site with lots of material. As a professional, he charges for the best parts of that material, but there are a plenty free tutorials

https://adamblockstudios.com/

http://caelumobservatory.com/

Andreo has this site

http://www.deepskycolors.com/rba_home.html

It also has interesting tutorials with more advanced content.

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I use APP for Pre Processing, but it is the same thing. Here is what works for me:

 

(The algorithm can only work on what you give it. It needs your guidance to work on pieces of sky background that should be evenly lit, but aren't because of light pollution)

- Stretch the image to the extreme (in lightness and saturation), so you see what is going on. Where is the sky background? Are there faint traces of nebulosity, faint spiral arms, maybe IFN?

- Place points  small enough so you have an even patch, large enough to have sufficient statistics in the places where you think there should only be an even sky background. Less is more. This is the most important thing imho.

- Do the calculation and look at the correction model. Is it smooth? It should be. 

- When you have integrated images over multiple nights, the gradient in your image can be quite complex instead of a gradial transition and as a result, the correction model will need to be a bit less smooth.

- Confronted with this, place additional points along either side of the transition in light pollution to help the algorithm in modelling the complexity.

- Look at the model again. Then look at your image. Totally flat is not what you will get. Remember that the background in you final rendition will be much darker than this.

 

It is not a black art, but it is somewhat of a craft and as in any craft you have to practice it a lot to get a feeling for it.

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On 16/05/2020 at 11:38, tingting44 said:

Just come across an interesting watch, this guy uses huge samples, and only samples the outside of his image, kind of makes sense, I'll have to experiment to see for my self but he seems to get good results...

 

 

Shauns videos are really helpful and he a nice relaxed way of explaining without a load of waffle

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