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Flame and Horsehead Nebula (IC434) in HaRGB | by Andrew Klinger
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Flame and Horsehead Nebula (IC434) in HaRGB


OTA: William Optics GT81 w/0.8x reducer (382mm fl at f/4.7)

Mount: Orion Sirius EQ-G (HEQ-5)

Guidescope: Orion 50mm guidescope

Guiding camera: Orion StarShoot Autoguider

Imaging camera: ZWO ASI1600MM-Cool









Location: Flower Mound, TX for Ha(Bortle 7), Atoka, OK for RGB(Bortle 3)

Dates: 10/23/17, 11/24/17, 12/8/17, 12/12/17

Gain: 200 Offset: 50 for Ha

Gain: 76 Offset: 15 for RGB

Camera temp: -20C

Ha: 164x300" Astrodon 5nm

R: 25x180"

G: 22x180"

B: 26x180"

Total integration time: 17hrs 19min

64x darks per calibration (master from library)

30x flats per calibration

200x bias per calibration (master from library)



Batch PreProcessing script to generate calibrated images

StarAlignment to register all frames to the reference

LocalNormalization of all registered frames (per channel)

ImageIntegration of each channel

DrizzleIntegration of each channel

DynamicCrop each master

DBE each master


Ha Processing:


HistogramTransformation x2

Duplicated the image to create a starless version, using a starmask and several iterations of MMT and MT. Then pushed the faint nebulosity in the starless version using PixelMath expression: "1-(1-$T)*(1-$T)"

Combined the starless version with the image using PixelMath expression "F=0.2; (1-(1-$T)*(1-s)*F)+($T*~F)" (s=starless photo).

LocalHistogramEqualization with inverted starmask

MLT for sharpening

HistogramTransformation to move black point in


RGB Processing:

Using PixelMath, blended linear Ha with linear masters (50% into R, 10% into B, 5% into G)

ChannelCombination to create RGB


SCNR green

TGV and MMT noise reduction (via Jon Rista's method)

HistogramTransformation x3


Combined Ha to RGB using LRGBCombination with Ha applied as a mask

HistogramTransformation to stretch image brighter

PixelMath with a StarMask to add the original RGB stars back into the image (they looked weird beforehand)

CurvesTransformation for a small stretch

SCNR green

CurvesTransformation for slight saturation


Resampled to 50% for web posting

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Uploaded on December 18, 2017