PixInsight Beginner's Guide: How to Process Your First Astrophotography Image
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Why PixInsight?
If you have been shooting deep sky astrophotography for any length of time, you have probably heard people talk about PixInsight. It is the gold standard for processing astronomical images, built by astrophotographers specifically for astrophotography. Unlike Photoshop or Lightroom, every tool in PixInsight was designed to handle the unique challenges of faint nebulae, noisy data, and light-polluted skies.
PixInsight costs around 300 euros (roughly $325 USD) as a one-time purchase with no subscription. You get lifetime updates for the current major version and can run it on multiple computers across Windows, macOS, and Linux. If you want to test it first, there is a free 45-day trial with full functionality.
This guide walks you through processing your first deep sky image in PixInsight, from raw stacked data to a finished result. We will keep things simple and focus on the essential workflow that covers 90% of what beginners need.
What You Need Before You Start
Before opening PixInsight, you need raw data from a night of imaging. A typical imaging session produces several types of frames:
Light frames are your actual exposures of the target. These contain the signal you want, plus noise, thermal artifacts, and optical defects.
Dark frames match your lights in exposure time, ISO/gain, and temperature, but are taken with the lens cap on. They map the thermal noise pattern of your sensor so it can be subtracted.
Flat frames are short exposures of an evenly illuminated surface (like a white t-shirt over the telescope or a flat panel). They correct for vignetting and dust spots in your optical train.
Bias frames (or dark flats) are the shortest possible exposures with the cap on. They capture the baseline electronic read noise of your sensor.
You do not strictly need all four types to get a result. Lights alone will work, but calibration frames dramatically improve image quality. If you are just starting, prioritize darks and flats.
Step 1: Stacking with WBPP
Weighted Batch PreProcessing (WBPP) is PixInsight's all-in-one stacking script. It handles calibration, registration (alignment), normalization, and integration (stacking) in a single automated pipeline.
To open WBPP, go to Script > Batch Processing > WeightedBatchPreProcessing.
The WBPP interface has tabs for each frame type. Here is the process:
- Click the Lights tab and add all your light frames
- Click the Darks tab and add your dark frames
- Click the Flats tab and add your flat frames
- Click the Bias tab and add your bias frames
- In the bottom right, set your Output Directory to a folder with plenty of free space (stacking generates large intermediate files)
- Select a Registration Reference Image from your lights. Pick one from the middle of your session, as it tends to have average tracking quality
- Click Run
WBPP will analyze each frame, reject bad ones, calibrate the lights using your darks, flats, and bias frames, align everything to your reference frame, and stack the result. This process can take anywhere from 15 minutes to over an hour depending on your data volume and computer speed.
When it finishes, you will have a master light file. This is your stacked image, and it will look very dark. That is normal. All the signal is compressed into a narrow range of pixel values.
Step 2: Crop the Stacking Edges
After stacking, the edges of your image will have artifacts from the alignment process where frames did not fully overlap. Use DynamicCrop to trim these away.
Open DynamicCrop from the Process menu (Process > Geometry > DynamicCrop). A resizable rectangle will appear on your image. Drag the edges inward until the stacking artifacts are excluded, then apply the process by dragging the triangle icon onto your image.
Step 3: Background Extraction
Light pollution and optical gradients create uneven backgrounds in your image. PixInsight offers two tools for this: AutomaticBackgroundExtractor (ABE) and DynamicBackgroundExtraction (DBE).
For beginners, ABE is the simpler choice. Open it from Process > BackgroundModelization > AutomaticBackgroundExtractor. The default settings usually work well. Apply it to your image and you should see a noticeably more even background.
If ABE leaves residual gradients, try DBE. It gives you manual control by letting you place sample points on areas of sky background (avoiding stars and nebulosity). It takes more effort but produces cleaner results on challenging data.
Step 4: Color Calibration
If you shot with a color camera (OSC or DSLR), your image needs color calibration to produce accurate, natural colors. PixInsight has two approaches:
SpectrophotometricColorCalibration (SPCC) is the modern, preferred method. It uses an online star catalog to match the actual spectral properties of stars in your field. Open it from Process > ColorCalibration > SpectrophotometricColorCalibration. You will need to plate-solve your image first (see the ImageSolver script under Script > Image Analysis). Once plate-solved, SPCC will automatically produce accurate color balance.
PhotometricColorCalibration (PCC) is the older alternative that also uses star catalogs but with a simpler approach. It works well and is easier to set up if you have trouble with SPCC.
For mono cameras with narrowband filters, color calibration works differently and typically involves manual channel combination, which is beyond the scope of this beginner guide.
Step 5: Stretching the Image
This is where your dark, linear image transforms into something recognizable. Stretching maps the narrow range of faint pixel values into a visible range.
HistogramTransformation (HT) is the classic approach. Open it from Process > IntensityTransformations > HistogramTransformation. You will see a histogram with most of the data bunched up on the left (shadows). Drag the left triangle (shadows clipping point) to just left of where the histogram data begins. Then drag the middle triangle (midtones) to the left to brighten the image. Apply in small increments rather than one aggressive stretch.
GeneralizedHyperbolicStretch (GHS) is a newer, more sophisticated stretching tool that gives smoother results. Many astrophotographers now prefer it over manual histogram stretching. It is available as a process in recent PixInsight versions.
The key with stretching is patience. Multiple gentle stretches produce better results than one aggressive one. If the background gets too bright, you can use HT to push the shadows back down between stretches.
Step 6: Noise Reduction
Deep sky images are inherently noisy, and stretching amplifies that noise. PixInsight has powerful noise reduction tools.
NoiseXTerminator is a paid third-party plugin (by Russell Croman) that uses AI-based noise reduction. It is widely considered the best option available and is extremely easy to use: apply it with default settings and adjust the denoise strength to taste. It costs around $60 and is worth every penny if you are serious about astrophotography processing.
If you prefer free built-in tools, MultiscaleLinearTransform (MLT) handles noise reduction well, though it requires more manual tuning. You can target specific wavelet layers to reduce small-scale noise while preserving larger structure.
Step 7: Star Reduction (Optional)
In many deep sky images, stars can overpower the nebulosity or galaxy detail you want to showcase. StarXTerminator (another Russell Croman plugin, around $60) separates stars from the background, letting you process each independently and recombine them with controlled star brightness.
The built-in alternative is to use morphological operations or the older StarNet++ integration, though these are less refined.
Step 8: Final Adjustments
With the heavy lifting done, you can fine-tune your image:
CurvesTransformation lets you adjust brightness, contrast, and color saturation with precision. Use the lightness curve to boost contrast in the midtones, and the saturation curve to bring out color in nebulae.
LocalHistogramEqualization (LHE) or HDRMultiscaleTransform can bring out detail in bright nebula cores without blowing out highlights.
ColorSaturation lets you selectively boost or reduce saturation in specific color ranges, which is useful for enhancing the red of hydrogen-alpha emission or the blue of reflection nebulae.
Saving Your Result
PixInsight uses its own XISF format natively, which preserves processing history and metadata. For sharing and printing, export to TIFF (16-bit for maximum quality) or JPEG/PNG for web use.
Go to File > Save As and choose your format. For TIFF, select 16-bit unsigned integer. For JPEG, a quality setting of 90 or higher keeps compression artifacts minimal.
Common Beginner Mistakes
Stretching too aggressively in one step. Multiple gentle stretches always produce better results than one big push. If your background turns gray or noisy, you stretched too hard.
Skipping background extraction. Gradients from light pollution become very obvious after stretching and are much harder to remove at that point. Always handle gradients before you stretch.
Not taking calibration frames. Dark frames and flat frames make an enormous difference in final image quality. Walking indoors without shooting calibration data is throwing away easy quality gains.
Over-processing. It is tempting to push noise reduction and sharpening to extremes. A slightly noisy but natural-looking image is always better than an over-smoothed, artifact-ridden one.
PixInsight Resources
The PixInsight community is active and generous with knowledge. The official PixInsight forum is the best place for troubleshooting. YouTube channels like Astro Backyard and Galactic Hunter offer excellent video walkthroughs. For a comprehensive reference, the book PixInsight Workflows by Max Dobres provides step-by-step guides for various target types.
Once you are comfortable with this basic workflow, you can explore more advanced techniques like narrowband processing, mosaic stitching, and deconvolution. But this foundation will carry you through the vast majority of deep sky targets.
To inspect the EXIF and camera metadata embedded in your finished astrophotography images, try ExifGrabber for instant, private metadata extraction right in your browser.