Welcome to SpectraVision
SpectraVision is a scientific night photography color analysis tool built by Utah Astrophotography & DinoSpectra. It runs entirely in your browser — no install, no server, no upload. Your photos never leave your device.
Most photography tools require you to judge colour by eye. SpectraVision gives you scientific numbers — Kelvin, R:G:B ratios, FWHM, SQM — so corrections can be verified without trusting your display or your eyes. This makes it uniquely useful for colorblind photographers.
This tutorial covers every feature. Each section includes interactive demos, quizzes, and real worked examples. Use the sidebar to jump to any topic.
Loading Your Photo
JPEG, PNG, WebP.Use Safari for best performance on iOS. Tap the Share button → “Open in Safari” if you open the file in another app first. The tool works offline once loaded.
Open SpectraVision and load a Milky Way photo with visible light pollution on the horizon. This tutorial uses Grand Teton NP as its reference example throughout.
Navigating the App
The screen is split into two panels. The left panel always shows your photo. The right panel is the analysis area, navigated by the tab strip.
All 20 Tabs
Spatial Analysis
The SPATIAL tab divides your image into a 5×4 grid of 20 cells. Each cell shows three numbers simultaneously: colour temperature in Kelvin, Adams Zone, and colour preservation percentage.
Reading the Grid
Each cell’s Kelvin reading tells you whether that region of your image is warm (light pollution) or cool (clean dark sky). Upper-left sky cells should read 8000–12000K. Lower cells near the horizon reading 2200–5000K confirm sodium or LED pollution.
Colour preservation is the percentage of colour information surviving in that zone. A reading of 30% means 70% of the pixel data in that cell is flat, crushed, or indistinguishable from noise. Upper sky cells should be 65–85%. Heavily polluted foreground cells often drop below 30%.
Tap any cell in the 5×4 grid. The detail panel below the grid shows the exact Kelvin, Zone, and preservation for that cell. Try comparing an upper sky cell vs a lower foreground cell on your image.
Warm band at the bottom = light pollution gradient. If bottom row reads 2500–4000K and top row reads 9000K+, you have a strong pollution gradient needing correction. Uneven colours across the top row = possible gradients from multiple pollution sources at different compass bearings.
Zone System
Based on Ansel Adams’ Zone System. Click any zone bar in the histogram to highlight those exact pixels overlaid on your photo.
The 10 Zones — Click to explore
What to expect in a night photo
For a well-exposed Milky Way shot: most pixels should be in Z1–Z4 (dark sky with texture). A spike at Z0 means crushed blacks with no recoverable detail. Bright star cores in Z8–Z9 are acceptable. A large proportion in Z5–Z6 usually means overexposure or heavy light pollution brightening the sky.
Waveform Monitor
The WAVE tab shows a broadcast-standard luminance waveform with a full R/G/B channel parade below it. Everything is plotted at native retina resolution — the same quality as professional video scopes.
Reading the Luma Trace
Reading the Channel Parade
The three smaller traces below show R, G, and B channels independently. For a correctly balanced dark sky:
Your sky is warm — light pollution is shifting the colour balance. Use the Sky Colour Temp and Light Pollution Remove sliders in the CORRECT tab until B sits above R.
3D Vectorscope
The SCOPE tab plots every pixel in your image as a dot in 3D hue space. Drag to rotate, pinch or scroll to zoom. Toggle Auto-rotate for a continuous 360° view.
A tight, roughly spherical cluster near the neutral axis means low saturation and a well-balanced image. Most dark sky photos should look like this — subtle colours, not vivid ones.
A tail extending toward the R/Y quadrant means warm light pollution is pulling those pixels away from neutral. The longer the tail, the more severe the pollution. After correction, the tail should collapse back into the main cluster.
Isolated bright dots are individual stars plotted by their spectral type. Blue O/B stars appear toward the B axis; red M-class stars appear toward the R axis. Yellow/orange G/K stars cluster in between.
The vectorscope is one of the most powerful pollution diagnostic tools. An image with no visible pollution on the histogram can still show a clear orange tail on the vectorscope, revealing a subtle colour cast that the eye and histogram miss.
Star Analysis & Focus Quality
Star Detection
SpectraVision automatically detects point sources and measures them. The STARS tab shows star count, spectral type distribution, Bortle scale estimate, and a light pollution direction compass.
FWHM & Focus
The FOCUS tab measures Full Width Half Maximum — the standard scientific measure of star sharpness.
Light Pollution & Sky Quality
Detected Source Types
The SOURCES tab identifies the spectral signature of detected pollution:
Sky Quality Meter (SQM)
The SQM tab estimates a standard Sky Quality Meter reading in mag/arcsec² from your dark zone pixels, plus an A–F composite site grade combining SQM, sky temperature, and pollution percentage.
Making Corrections
The CORRECT tab has five live sliders. Every adjustment immediately updates the image and all analysis tabs. Drag a slider and watch the waveform and zone histogram change in real time.
The Five Sliders — Interactive Demo
All Sliders Explained
Shifts the colour temperature of dark sky zones. Increase (cool) to counteract warm/orange sodium pollution. Target: 9000–11000K for true dark night. This is the primary control for light pollution correction. Start here before touching any other slider.
Subtracts the dominant warm pollution colour from dark zones. Works best when a specific source (sodium, mercury) has been detected. Try 30–70% for strongly city-lit skies. Use in combination with Sky Colour Temp.
Raises the floor of dark zones without affecting highlights. Use when shadows are completely crushed (Zone 0 spike in the histogram). Recovers texture detail in near-black areas. Keep below 40 for natural-looking results.
Increases or decreases colour saturation specifically in shadow zones. Positive = adds colour to dark areas. Negative = neutralises colour casts in shadows. Useful when shadows have an unwanted tint after light pollution removal.
Reduces blowout in the brightest highlights (bright star cores). Prevents star centres from clipping to pure white, preserving slight colour information. Gentle use only — high values can make bright stars look flat.
Split Before/After View
Tap ⇄ Split B/A in the CORRECT tab to see original and corrected side by side with a draggable divider. This is the best way to judge how much the correction has changed the image. The split view respects any active overlays.
Colour Blindness Balancing
The CVD tab is designed for colorblind astrophotographers who cannot rely on colour perception to judge sky balance. It replaces colour judgment entirely with scientific numbers.
The CVD tab UI does not apply a pink or green tint. Adding colour tints to the interface would make it harder for colorblind users to read — the opposite of accessible design. Instead, the tool uses numbers, symbols, and text so no colour perception is needed to operate it.
Step 1: Select Your CVD Type
Choose the option that matches your condition. The image is immediately rendered through the Vienot 1999 simulation matrices, showing it as you actually see it.
Steps 2–4: Live Balance Verdict
The verdict box and three gauges update every frame as you move the sliders. All three must show green before the image is balanced.
Click the gauges above to cycle through states — see how all three look when fully balanced.
Sky Presets
Channel Enhancement
The Kelvin slider alone cannot reveal all the colour features of the Milky Way. Several important astronomical signatures exist outside the Kelvin scale. Step 5 of the CVD tab adds three independent channel boost systems.
Why Kelvin Is Not Enough
H-alpha emission nebulae (656nm red), airglow OI 557.7nm (green), and OIII 501nm (blue-green) are specific spectral line emissions — not blackbody radiation. They don’t follow the Kelvin curve at all. Cooling the sky from 3000K to 10500K will not make these features visible to a colorblind photographer who cannot perceive those wavelengths.
Channel Gain Tab
Three independent sliders boost R, G, or B across the whole image. For Protanopia: boost R to 80% and red nebulae, red stars, and warm dust lanes become visible. For Deuteranomaly: boost G to 70% and airglow OI 557nm becomes distinguishable from the background.
Emission Lines Tab
Rather than targeting specific pixel wavelengths (cameras don’t store that data), SpectraVision detects each emission type by its R:G:B signature. H-alpha appears as red-dominant pixels with low G and B. Airglow appears as green-dominant pixels at mid brightness. OIII appears as blue-green with low R. The slider then boosts those identified pixels selectively.
Auto Enhance Presets
False Colour Assist
Step 6 of the CVD tab. Remaps colours you cannot perceive to colours you can, using full HSV hue rotation per CVD type. For editing only — disable before exporting your final image.
Red-dominant pixels (H-alpha nebulae, red stars, warm dust lanes) in the 330°–35° hue range are shifted toward yellow-orange (50°–70°). This places them in the visible range for protanopes without altering the sky blue or overall image structure.
Green-dominant pixels (airglow OI 557nm, green nebulae) in the 90°–155° hue range are shifted toward cyan-blue. This makes them distinguishable from both the warm pollution glow and the sky blue, because cyan sits between those two and is visible to deuteranopes.
Blue-dominant pixels in the 220°–285° range are shifted toward green-cyan. The deep blue of night sky that appears grey to tritanopes becomes a visible green-teal, making sky quality assessment much more reliable.
Since no colour is visible, the remapper converts all colour information into luminance contrast variation. Emission line features become brightness differences — H-alpha regions become slightly brighter, airglow regions slightly darker — revealing structure that would otherwise be invisible.
False Colour Assist is an editing aid, not a colour correction. If you export your image while False Colour is active, the remapped colours will be baked into the file. The warning banner in the CVD tab stays visible whenever it is on.
Print Calibration
The PRINT tab diagnoses why prints come out dark or with colour shifts. It builds a compensation profile through six interactive steps.
Night Shift (iPhone/Mac) and Night Light (Windows/Android) add 800–3200K of warmth to your entire display. If you correct your sky to look balanced with Night Shift on, the image is actually several thousand Kelvin too cool. When you print it, the print will look cold and blue. Always disable these before doing any colour work.
How to disable: iPhone/iPad: Settings → Display & Brightness → Night Shift → off. Mac: System Settings → Displays → Night Shift → Schedule: Off. Windows: Settings → System → Display → Night Light → toggle off. Android: Settings → Display → Eye Comfort Shield → off.
White Balance Eyedropper & Selective Colour
WB Eyedropper (WB tab)
The WB tab also automatically finds all near-neutral pixels across the whole image and shows their average Kelvin. This gives you a second reference point without clicking anything.
Selective Colour (SELECT tab)
Region Analyzer & Exposure Calculator
Region Analyzer (REGION tab)
Analyses just a user-defined area of the image rather than the whole frame.
Exposure Calculator (CALC tab)
Calculates maximum shutter speed before stars trail using both the NPF rule (more accurate) and the older 500 rule.
The 500 rule only uses focal length (500 ÷ focal length = max seconds). The NPF rule also accounts for aperture and sensor pixel pitch, giving a result that is typically 30–60% more conservative and more accurate for modern high-resolution sensors. Stars near Polaris allow 3–4× longer exposures than equatorial targets.
EXIF Data & Analysis Reports
EXIF Data (EXIF tab)
SpectraVision reads EXIF data from the raw file bytes. No data is sent to any server. The EXIF tab shows: camera make and model, shutter speed, aperture, ISO, focal length, date/time, and GPS coordinates (if recorded).
EXIF data is only available in JPEG files. PNG files do not include EXIF metadata. If you export from Lightroom as PNG, you will not see EXIF data in SpectraVision.
Analysis Report (REPORT tab)
Generates a complete scientific summary including: sky Kelvin, SQM, dynamic range in EV stops, light pollution percentage and source type, stars detected, FWHM, full zone distribution, and EXIF data.
Exporting Your Image
Tap Export ▼ in the top toolbar and choose PNG or TIFF. A progress bar appears immediately confirming the export has started.
The exported image reflects any active corrections, CVD channel enhancement, and emission line boosts. If False Colour Assist is on, it will be baked into the export — always check that it is Off before exporting a final image.
After tapping Export, your browser may show a download prompt or open the image in a new tab. If it opens in a new tab, long-press the image and choose “Save to Photos” or “Save to Files.”
Sky Colour Temperature Targets
These are the scientifically calibrated targets built into SpectraVision’s CVD gauges and presets.
True dark sky is predominantly illuminated by starlight and faint airglow. Starlight averaged across the whole sky skews blue because O and B class hot stars are intrinsically bright. The absence of warm artificial lighting allows the blue contribution to dominate. Any condition where R > B on the waveform parade means warm pollution is present.
Glossary
Tutorial Complete
You’ve covered all 20 tools in SpectraVision. Load a night photo and start analysing!