Originally posted by fewayne: Pete, would you mind elucidating the tools you used to "strip off obstacles...by their frequency"? I get that it'll be awhile before the tutorial, but just a hint would help me to crash around playing with things.
Thanks for these gorgeous images. I'm not sure exactly why I find these in particular so compelling, but I really am deeply touched emotionally by them.
Thank you for your nice comment fewayne.
I know I promised to publish a tutorial but when I started I noticed that ist a lot more work to produce it on the level I had intentioned. Then my spare time was eaten up by job, family and other things that were more important end of the year. And also I noticed that I am still not ready with my workflow and can not finally conclude yet.
I can not got into the details here but plan to give some kind of basic recipe in another thread here in the group this weekend. So here just a short description of the main process:
Under the balance doing a frequency separation is nothing more than taking a layer, copying it, changing someting in the original and extracting the differences between the original and the changed version onto a separate layer. It does not matter what changes you make, the differences - lets call them residuals - will end up isolated on a distinct layer. In my workflow I save the residuals for later use and work on with the changed layer.
Imagine you have two copies of a layer in PS with stars and use the dust & scratches filter in an apropiate way with the stars selected to eliminate them in the original layer. After applying the filter you have a layer without stars and on top of it in the copy a layer with stars. You then go to this unchanged layer, open picture ->apply image. There you refer to the changed layer and choose "subtraction" in the dropdown list. And in a 16 bit image you must set the scale to 2 and the offset to 128.
After clicking OK you have extracted only the differences between the former original and the filtered version to the top (residual) layer and have the no-star-layer below. The residual layer has the appearance of the result of a high pass filter process. But changing the residual layer mode to linear light you see the complete picture again. You can then take the residual layer with the stars away (but preserve it) and work on with the starless layer. If you apply that principle step by step with big stars, small stars, star halos and noise you strip working layer down until it only contains the background (more or less) free of noise, halos and stars. All the residual layers with the "differences" of the elimination steps are saved but inactive in a "residuals" layer group.
You can then agressively stretch the background image layer to work out the fine dim details and structures you else would never get under control without affecting the stars too much. If you are done with that you can take the resitual layers on top in linear light mode and gradualy blend them in to have a complete picture with stretched background and unaffected stars.
The principle itself is easy to apply and straight forward. How and if it works depends on external factors like star density and overall image quality. And because the background is stretched to the max it is essential to use flat frames with the stacking and to have techniques to eliminate colour and brightness gradients at the very beginning of the workflow. But also it is necessary to have a good understanding and a bit skill in PS mainly in the decent use of standard technologies in PP like propper and sensitive handling of levels and curves tools, masks etc. That is why I referred to the excellent tutorials from e. g. Scott Rosen in other posts where one can learn this.
Cheers
Pete
P.S. While working on the background layer without stars the scenery often appears very shabby. It helps and keeps you optimistic when you place a copy of the stars residual layer as the top layer in linear light mode. Switch it on and of to always have an impression of the whole image while stepping foreward in processing the background.
