Astrophotography workflow for simple batch conversion of raw lights? My results still appear de-saturated.

Hi, I’m new to RT and I’m trying to figure out how to get a straightforward conversion of my raw frames with camera-specific false color correction. I basically want to use RT to get the pure data with the color fixed based on my specific camera sensor. The goal would be to save a one-size-fits all profile and re-use it for quick conversion of future batches.

The software has my camera + lens combination, and I’m trying to figure out what Batch Edit steps are necessary before sending the output to stack in DSS and edit in GIMP. But by the time I finish stretching in GIMP, I still need to boost saturation a ton to get much color visibility.

At the moment I’m doing:

  • Exposure tab: default settings

  • Detail tab: default settings

  • Color tab: default settings (but make sure “White Balance->method=camera” and “Color Management=auto matched camera profile” are selected)

  • Advanced tab: default settings

  • Transform tab: it has “Lens Profile Correction=automatically selected” by default. I’m pretty sure this eliminates the need for flat frames

  • Raw tab: Demosaicing method=IGV (LMMSE is better?), False color suppression steps=2, Dark Frame = choose a file in my Darks folder and then choose auto-selection (this will supposedly use all of the darks in the folder, but I receive no indication this is what it’s actually doing.

Thanks for any hints!

Hello @chrisdean11, welcome to the forum!

I have not tried DSS for stacking. I do astro stacks using Siril, that is raw → fits conversion, registration of fits files, stacking of fits files, stacked fits → tiff conversion, all in Siril (lights, dark, flats, bias). I then process further in GIMP using the tiff files.

RT is great software and I use it a lot, but I rarely do astro stacks with RT output like tiff files. I prefer to convert the raw files in the astro stack application (Siril in my case), directly.

What is it you what to accomplish with RT, in your case? I do not fully understand “…use RT to get the pure data with the color fixed based on my specific camera sensor…”.

Edit:

Edit: I get better results with my own flat frames in stacking program adapted to the exact properties of my copy of the lens, when it comes to vignetting. The astro streching in post processing magnifies any residual error.

Edit: RT has its own flat field correction built in, but I have not used it. However I am sure there are users who know the function and can advice if it is useful in your astro stack case. Flat-Field - RawPedia

Hi, thanks for the feedback. What I’m referring to is kind of hard to explain in detail, but the filters on Bayer camera sensors are imperfect, for instance the red cells let in some amount of blue and green, and so on. So just straight debayering a raw image can result in muted colors. Especially in very faint images like astro.

However, there exist color correction matrices which are customized for every specific camera/sensor, which attempts to fix this problem. Adobe Camera Raw uses these (as does some free software like RT and Darktable, but not DSS and I don’t think Siril either), and it can restore some of that color without having to artificially boost the saturation later on.

Here’s a post on the Cloudy Nights forum which describes the issue better than I can:

In other words, what I’m trying to accomplish is to establish a step before stacking in DSS, where I take all of my light frames and run them through raw conversion/false color correction as a first step. My desired workflow is:

Raw images → convert/correct in RT → stack in DSS → edit in GIMP

RT has a good batch editing feature, along with being able to save and reuse a profile. So it seems like a good tool for automating raw conversion of astro photos for processing in other software.

Edit: I compared the results with/without my RT conversion step, and it does appear to have slightly more color detail but it’s hard to notice the difference. I still have to crank up the saturation in GIMP. I guess what I’m asking is whether there are any other settings I should try changing that I hadn’t listed in my original post.

@chrisdean11, thank you for the Cloudy Nights post. Interesting, I will check it out. I am sure it will also enable other forum readers to help you.

OK, also my camera and lens is automatically detected by RT. I have Color_tab | Color Management | ‘Auto matched color profile’. It is also possible to manually pick up a dcpprofile using ‘Custom’.

At this stage, my biggest color problem is that I am using a regular camera with IR filter (Canon 5D mk IV), so I loose most of H-alpha red.

Edit: I have the same issue with low saturation. I think this is standard in astro photo (the deep sky objects are kind of pale). It is highly interesting if converting raw->tiff in RT and then do the stack actually improves final result. I agree that every little gain counts (besides dark, flat, bias corrections and background extraction…). This makes astro photo both hard and interesting. Again, in my case the biggest issues are the IR filter and the light pollution, where I live (suburb, suburb-rural transition).

I’ve also come across this detailed article from RN Clark’s website, describing the RT settings he uses specifically for astro.

https://clarkvision.com/articles/astrophotography-with-rawtherapee/

It’s from a few years ago using version 5.4, so I’m going to use it as a starting point and try playing with some of the newer features (such as Capture Sharpening) in addition.

Just skimmed that thread, post #16 explains what that matrix is all about.

The matrix doesn’t correct color, it describes the camera’s response so that the image data can be converted to smaller gamuts for working and rendition. Like post #16 says, the camera matrix describes conversion of the camera data to XYZ, which is an intermediate destination. From there, a second conversion is applied to get the data to whatever destination colorspace is desired. Usually, that’s a large-gamut working space for editing. Then when the image is ready to be exported for viewing, a second conversion from working to the rendition gamut is applied. Again, XYZ is used as an intermediate; this allows color profiles to just worry to and from XYZ, and not every other profile in existence.

Yes but in astrophotography you don’t really need it. Color correction is usually done thanks to the photometric analysis.