Gimp, Photoshop, StarTools, Raw Therapee, 32 bit processing….
also links to excellent and key tutorials to follow as you process your images
🔭😊⭐️This is a compilation of ongoing notes that I am creating and continually tweaking on the topic of image processing… as I continually follow the arduous path in learning this difficult but wonderful skill. Associated and included are key sites that I have found particularly useful.
Hope this will serve equally useful to you, my fellow hobbyists…
My Overall Approach to Image Processing:
I have been using the older version of Luminar 2018 for some time and actually go to it to tweak very specifically regions for detail, luminosity, saturation contrast…essentially all these attributes and so much more, applied to specific regions by a size, softness and opacity adjusted brush….so you have the ability to do global or local adjustments using a brush and with or without an option to do so in layers as well.
I prefer to work initially in 32 bit image processing…so currently I use Gimp, RawTherapee. Working in 32 bit allows more detail to be gotten when you do your initial stretches and hence more dynamic range in the final result….
I take the post processing as far as I can with these software in 32 bit ….then go to a combination of other software for final tweaking, like Photoshop, Siril and Luminar which save in 16 bit. I have found that downsizing the image from 32 bit to 16 bit actually reduces the noise in the image not to mention renders a better dynamic range even after downgrading to 16 bit. In fact it is also a way to spend less imaging time and still be able to obtain a desirable result.
I would love to know your approach to image processing…😊
Here he does not deal with any star color…just size with respect to masking.
He does not deal with star color with his created masks in this vide.
……probably best to keep the gain low and use short exposures and stack lots of frames. Then, if you want to go really deep just add some frames with longer exposures and create an HDR. However, you can get perfectly adequate images without going to HDR.
I too struggle with this,but I have found that shorter subs help. I use 150s subs for the RGB background. After you’ve blurred the stars to get the colour, try a little colour saturation (in your program of choice) and then use a sharpening tool to make them nice and solid again. I find if I do that, followed by a size reduction step or two for the larger stars, the stars star to look a bit more colourful.
Use Noels ‘increase star colour’ along with decent gaussian blur to colour up but soften the stars in bottom layer.
Set the top layer to ‘luminosity’ to restore sharpness.
The thing that made the difference for me was making a mask, just allowing work on the bigger stars, then switching to Lab mode and using the saturation slider a little… I thinks its come out pretty good… compared to my first go. It does something odd to the yellow stars… I got a few bicolour yellow blue stars that had to be erased! I have a way that works
*❤️Read that should make a copy or original image and from that copy first work on stars in the image to get color and then take out the stars as a layer.
Maybe during the process of stretching the image could highlight select the stars and copy and past them into a new layer…that is make them visible in that layer….turn those layers off until needed…could then recombine the stars into one star only layer to retain the size and star color or use opacity changes to bring out the stars. Also can use these star layers and merge and make a star mask to further process the main image while not affecting the size of the stars…that way when the star layer or layers are revisible in the image there will not be halos or star color changes to affect the star layer or layers contributing to the overall final image.
How to add back to the image the removed stars:
Process the No Stars image in the usual way, then process the original image so that just the stars show and not too much background nebulosity. Then copy this image and paste it in a new layer over the top of the starless image and set the blend mode to either Lighten or Screen…..whichever one works best. (Not sure however how the Screen effect in PS or similar software would affect the colour.)
This one applied to Gimp….make a duplicate top layer turned off in case get fringing so you can increase a Gaussian blur which the other guy in Gimp does not perform.
This technique is good to follow and parallel in Gimp for diffuse nebula RGB or other colour images to preserve star colours and size while stretching to get detail in nebula. But does not talk of manipulation of colours.
This video over all would be the main one to follow covering all aspects of regions to control in post processing in an image.
This video shows how to create select stars only to increase star saturation. Also by using both a star mask and using the selective and inverted mask of the more compact nebula or galaxy can work on the main regions of background or nebula or galaxy separately.
Note that could also use the Gimp Quick Mask technique to select or invert regions to specifically process but the stars would be per this video.
❤️Gimp does not have arcs in stretch but if you do two arc sin curves with a levels in between in Gimp as in this tutorial but note the layer mode has to be changed….see tutorial. This will allow good stretch without loss of color.
Gimic plug-in better noise reduction than in native Gimp.
This video also has a good star reduction that can be done I Gimp. The highlighted stars could be used to specifically saturate and change the colours of the stars as well as to make a star mask.
Align Images In Gimp
The alignment tool works very well…note that in the astronomy plugins in Gimp there is an alignment script which might be good to try.
This alignment procedure will be necessary as I have not been able to align as yet different exposures in DSS….so then after stacking the images separately in DSS and separately post processing follow this step below to align the different exposure images in Gimp…..
Taking two images one faster exposure to reveal detail that would otherwise be blown out….These two following tutorials are excellent and through the use of layers and associated adjustments allow the creation of more dynamic depth in the image. Done in PS as in tutorial below could also be done in Gimp where the added advantage is being able to work in 32 bit….make sure the images are aligned before!
How to Expose the Foreground *
Tonal Adjustment….better than selective colour in PS.
Use Selective color in different ways to change colours and make masks
❤️❤️❤️When your regions are difficult to isolate can choose selective color see specifically 11.06 point in this video to make a mask according to the selective colours and change the color or any other characteristic of that region.
Select by color in Gimp….this looks as close as you can get by doing it in PS…this will work well…
Need to find the equivalent procedures in Gimp for this video….
Nik Collection…see exe files on Desktop (portable computer)
The ColorEfex.exe app in the Nik folder on my desktop is the best of all of the Nik apps and works on 32bit files….
HDR image is well done by the Nik collection…choose bracketing imaging on DSLR or take a series of different exposures with ZWO.
(The images would have to be aligned first and can do this in Siril)
The HDR program in this collection would probably be good for getting rid of the reflective regions on the moon….just take different exposure sets and stack them individually in DSS.
….❤️but this procedure will not let you separately adjust and tweak the different exposures in an ongoing way before they are merged….so better to align the different exposures in say Gimp and tweak the individual exposure layers there. This method combined with imaging with a red
and/or an IR pass filter will probably work very well.
Luminosity masks are basically layer masks that are built around specific tones in an image. They are derived from the image data itself, and focused on a specific range of tonal values. … Being able to selectively modify an image based on particular tonal regions can be a very powerful method of editing.
Note there is a luminosity mask creation script in Gimp. This can be used the same as selective colour in Gimp for processing very specific regions otherwise hard to do than by the lasso or tool selection….also note the luminosity masks that are automatically created in the script can be further changed by curves and levels.
Try using the luminosity masks created automatically with script in Gimp to perform precise and selective work on image….but will need a regular mask to protect specific regions or shapes in image.
Creating the Masks. To begin creating the masks we will need to first get a luminosity representation of the image. This is easily achieved by duplicating the base layer, and desaturating it using Luminosity as the conversion option.
The Quick Mask
Can use this to select or protect regions or to paste these regions on other layers….good for galaxy images and maybe star clusters like m13. Need to feather these regions or is it automatically done?
*❤️Could probably use this to inverse the galaxy mask selection to select the back ground then use either desaturate or levels to darken the background or the eye dropper to set black levels…could also do a Gaussian Blur to regulate the background night sky from pollution or dust.
A method that can select the background for processing to darker and no dust or light pollution: this involves drawing the lasso around the object….must do a feather of say 150 or less pixels so regions will not look harsh.
Also note that in PS there is an action script installed to get rid of space dust and does so gently and well…could do several repeats.
Excellent over all info in astro processing not really using as specific steps to follow.