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Post-Processing
Astrophotography post-processing enhances and refines images. This process involves multiple steps aimed at improving the image's visual appeal, reducing noise, and bringing out hidden details in images of celestial objects.
Learning Curve: Astrophotography post-processing is very much an artistic process and does have a learning curve. But there are plenty of tutorials and resources available online to help you learn the techniques. So fear not!
So what's real and what's fantasy/art?
You have to decide, as with any other branch of photography, “Am I a documentarian or an artist?” For a documentarian your question makes sense; if you’re an artist the question doesn’t make sense.
For the artist the questions is, “What is my style?” “What artistic license will I take?” and “What manipulation limits do I embrace in my work?”
We see the same thing in landscape photography. How much post-processing do my style and my ethics allow? All B&W photography and all infrared photography are artistic because they cannot approximate what the eye sees. Astrophotography is this way, too, especially when we use filters to enhance or reject certain wavelengths of light that an eye can't see.
Everything we’ve seen published from NASA’s Hubble and JWST are art because they include wavelengths our eyes can’t see. Because of this, NASA artists have made decisions about what colors that we CAN see will be used to represent the invisible-to-our-eyes wavelengths in images produced by those telescopes.
Furthermore, every jpeg file we see, even straight from a camera, has artistic decisions built into it. When you compare a jpeg from Nikon with one from Sony, Canon, or Fuji you will see differences, because some engineer/color scientist decided for each company how their color jpeg should look when they convert a “natural” raw file for human comsumption. Which one is “right?” It depends on each artist’s eye.
Glenn Sackett 2024/09/13 09:16
Software
Free unless otherwise indicated
*Free trial available for paid product
MacOS
Astro Pixel Processor* (€ 60.00 US$64)
Creative Cloud Photogeaphy -- (Photoshop and Lightroom) (US$20/mo)
Windows
iOS
Android
Step-by-step post-processing Seestar images with free software
Siril Tutorial -- Post-processing with Seestar script for beginners
Download free Siril program (Mac and PC) and Seestar script, then watch this step-by-step video
PixInsight Workflow for advanced users
PixInsight is expensive and inscrutable. But if you want the best out of Seestar images…
Stack RAW subframes with WBPP (Weighted Batch Pre Processing)
* Click +lights to add light subs
- Mixing 10, 20, and 30 second is OK. Adjust ‘Exposure tolerance’ to “20” in Post-Calibration tab
- To mix UV/IR Cut and LP subs use the EmissionLineIntegration script
- Integrate each set of subs separately, then register with WBPP, Background and gradient extraction color correct
- Extract red channel from LP set and label Ha
- Extract red channel from UV/IR set and label rub_r
- Perform liner fit on Ha using rib_rf as reference
- Create a star mask using StarXterminator (be careful not to let it remove bright Ha regions as if they were stars
- Use EmissionLineIntegration script on the U/IR integrated image (select Ha as narrowband on channel R)
- Jump to Standard Workflow
* In the top tab section, click ‘lights’
- Everything should be ‘checked’ except for the last one ‘Image Integration’ this will happen separately
- Presets upper right, Select ‘Maximum’ quality as your option there
- Add your ‘Output Directory’ in the lower right
- Purge cache, button lower right area
- Change 'Subframe Weighting’ to “PSF Scale SNR”
* In the top tab section, click, ‘Calibration’
- If you have different exposures do these steps for both
- Cosmetic Correction
- Confirm CFA DeBayer Method is 'VNG'
* In the top tab section, click, ‘Post-Calibration’
- Combine 10, 20, 30 second exposures set 'Exposure tolerance' to “20”
- Click Drizzle, use 2x for 1 hour or less, 3x or 4x for more. Set drop sizes 0,9
* Click ‘Run’
Standard workflow (YMMV)
- Dynamic Crop
- GradientCorrection and/or DBE, ABE, Graxpert
- Image Solver
- SPCC
- BlurXterminator
- SNCR
- NoiseXterminator
- StarXterminator
- Starless Image - GHS (GeneralizedHyperbolicStretch)
- Range Mask to isolate Nebula or Galaxy
- Curves for saturation
- Sharpen
- Stars Image - GHS
- Combine starless and stars:
- Tweak with Lightroom, Photoshop, GIMP was desired.
Definitions
Calibration:
Light frames: are the individual images you capture containing the light from your target object along with various sources of noise and artifacts.
Dark Frames: These are images taken with the same exposure settings as your light frames but with the lens cap on. They capture the noise inherent in your camera's sensor, which can then be subtracted from your light frames. Seestar handles this automatucally before DSO (Stargazing) images arfe captured
Bias Frames: Not requiered for Seestar, these are very short exposures (usually the shortest possible) with the lens cap on. They capture the read noise of your camera's sensor, which is also subtracted during calibration.
Flat Frames: Also not required for Seestar, these are images taken of a uniformly illuminated surface (such as a lightbox or twilight sky). They help correct for vignetting and dust spots on your camera sensor or optics.
Image Stacking:
Alignment and Registration: The software aligns and registers your light frames, ensuring that stars and other objects are precisely aligned in each image.
Stacking: The aligned images are then stacked together, which improves the signal-to-noise ratio and reduces random noise.
Image Enhancement:
Stretching: Stretching the image's histogram enhances the contrast and brings out faint details in the image. There are various stretching methods, including linear, non-linear, and curves adjustments.
Noise Reduction: Various noise reduction algorithms are applied to further reduce noise and smooth out the image.
Color Correction: This involves adjusting the color balance and saturation to achieve a natural or desired look for the image.
Sharpening: Sharpening enhances fine details in the image, but should be used carefully to avoid introducing artifacts.
Final Touches
Cropping and Composition: Cropping the image can help improve the composition and focus on the main subject.
Selective Adjustments: Use tools like masks and layers to apply adjustments to specific areas of the image.
Saving and Exporting: Save your processed image in a suitable format (e.g., JPG, TIFF or PNG) for further use or sharing.
post-processing.txt · Last modified: 2024/12/31 07:52 by tailspin