mcintyre_sj
Well-known member
I am having trouble balancing the colour for an image of the Veil Nebula taken with a Canon T2i with an Astrodon IR filter installed. I have 69 x 360s subs with bias, darks, and flats. I am following the drizzle integration workflow.
The subs look ok. Without the camera whitebalance, they are overly strong in green as expected.
If i manually apply the camera white balance formula, then the light sub has a colour balance that i expect with a reddish nebula and neutral background.
After stacking with all the calibration frames and using the drizzle integration workflow, the result is way too red, or way too little green.
I attempted a pixMath colour balance by normalizing the image to a reference image - linearly scale the background and star colours to match the reference image.
Then the background and stars look ok, although the background was neutral grey rather than redish.
But the nebula was green!!!
Nothing i do turns the nebula to the expected red.
As a faint hope, i swapped the red and green channels - RGB -> GRB.
And then the image colour looks ok. The nebula was now red with a little blue on the edge - as expected. The background was still neutral.
For reference, i stacked the image set with calibration frames using DSS. The colour balance from DSS was ok and matched the white balanced light frames.
For the images attached, i applied a curves function to stretch the images so things would show up better, but did not alter the colour balance. The colour therefore is what the process produced, less the stretch.
So what's going on here? How can swapping red and green channels produce a better looking image?
The subs look ok. Without the camera whitebalance, they are overly strong in green as expected.
If i manually apply the camera white balance formula, then the light sub has a colour balance that i expect with a reddish nebula and neutral background.
After stacking with all the calibration frames and using the drizzle integration workflow, the result is way too red, or way too little green.
I attempted a pixMath colour balance by normalizing the image to a reference image - linearly scale the background and star colours to match the reference image.
Then the background and stars look ok, although the background was neutral grey rather than redish.
But the nebula was green!!!
Nothing i do turns the nebula to the expected red.
As a faint hope, i swapped the red and green channels - RGB -> GRB.
And then the image colour looks ok. The nebula was now red with a little blue on the edge - as expected. The background was still neutral.
For reference, i stacked the image set with calibration frames using DSS. The colour balance from DSS was ok and matched the white balanced light frames.
For the images attached, i applied a curves function to stretch the images so things would show up better, but did not alter the colour balance. The colour therefore is what the process produced, less the stretch.
So what's going on here? How can swapping red and green channels produce a better looking image?
Attachments
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01_veil_light_360s_10_RGB_noWB.jpg319.1 KB · Views: 44
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02_veil_light_360s_10_rgb_wb.jpg326.9 KB · Views: 51
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03_veil_integrationDrz_noCB.jpg362.5 KB · Views: 39
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04_veil_pi_colourBalance_RGB.jpg392.2 KB · Views: 43
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05_veil_pi_colourBalance_GRB.jpg384 KB · Views: 49
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06_veil_dss_RGB.jpg368.1 KB · Views: 42
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