Hi Ray
I'll "full" reply your previous post, becouse someone may benefit from the answers... thanks for posting!
> Not sure if this question is ridiculous or not, but I'll ask anyway.
Not at all. You just had to read the documentation ;-)
>On the tutorial for 'Flat Fielding for Film Astrophotography' (see link).
>
http://pleiades-astrophoto.com/pixinsight/help/tutorials/filmflats-cmilovic/en02.html >It allows us to download the actual files from the tutorial. One of the files is the Synthetic Background Image.
>When manipulating my own images, how do I generate a 'Synthetic Background Model'?
>I don't understand where the synthetic background model comes from.
In the image processing jargon, sometimes we refer to this model as a "pseudo-flat". Having said that, the best way to create such pseudo-flat in PixInsight is to use the DynamicBackgroundExtraction (DBE) process. There you put sample boxes in your image, and the software interpolates a suitable function that will model the background. So, the result is a new image, that contains only this pseudo-flat.
Sorry if I was a bit confusious about that in my tutorial. I wrote it months before Juan decided to include DBE in the LE release, so that explains the lack of more direct references. I'll write a short tutorial about DBE, using the same image as an example, and I'll update this flat fielding tutorial.
> Also, is step two applied to both the Raw and Flat images?
Are you talking about the division with PixelMath? No. It is applied to the original image only (after linearization, of course). The linearization process is applied to both image and pseudo flat.
>And in step three where it says
>"applying an inverse transform with respect to the initial >midtones balance transform defined in Step 1."
>I'm not really sure what this means when it says "with respect >to the initial midtones". How do I apply an inverse transform >please?
I was trying to explain that we must "undo" the first midtones adjustement, made with Histograms. We want to apply Histograms again, and find a suitable midtones transfer curve that does the job.
As an inverse transform we call the adjustement that undoes the previous adjustement. For example, if you apply a midtones balance adjustement of 0.25, the inverse midtones adjustement is 0.75, becouse that will lead you to exactly the same image that you had previously to both processes.
In PixInsight's implementation of the midtones balance adjustement, the inverse transform is defined as 1-X, where X stands for the previuosly used value.
>There is a link down the bottom of this page (see below)
>filmflats.pi-psm
>I opened that link with PixInsight but couldn't see anything >different. What should I look for? What does it do?
You have to open it right-clicking in the main window's background and selecting the "Load Process Icons" option. A group of process icons will be opened in the background. If you cannot see them, becouse we have different screen sizes, press the "Arrange Icons" option. PixInsight will move the icons and arrange them in the bottom right corner of the window.
Now, double click any process icon (wich are "shortcuts" to process containers) and the interfase window of the process container will be opened. There you will see a list of the applied processes. To open them, and modify, double click over it's name.
Please read the documentation sections related to process icons and process containers to better understand how to work with them.
>I'm still a big noob with this stuff. Any help is appreciated.
>Basically, I want to get rid of sky glow and bits of light >pollution with PixInsight. I am also going to look into using the >DynamicBackgroundExtraction tool.
>Which one works better? The DBE or the Flat Fielding >technique?
They are two different things. DBE extracts the background, i.e. generates the pseudo-flat. Later, you can substract of divide by it (as described in my technique).
>Heres a link to an image I'm trying to improve.
>
http://www.members.westnet.com.au/raypalmer/milkyway.jpg >I want a dark background sky which is constant in color.
I remember it... Avoid to getting too close to the MW, becouse there are some "natural" gradients. Put your samples specially in the lower right quadrant of the image, and in all corners. Make use of symetries to fill the gasps.
