Adjusting Colors in a SHO Image

[bmimiaga]

I am new to NB imaging and post processing in PixInsight and have tried reading and viewing some good tutorials on YouTube about adjusting colors on a NB image but am still struggling to get the blue and gold colors as shown in the attached photo of IC1396 the Elephant Nebula (this is someone else's image). Here's my attempted post process steps using my master integrated frames;

1. Dynamic Crop to trim the edges of my SHO images.
2. Channel Combination to combine the SHO images into one RGB image.
3. Apply STF and Histogram Transformation to create a non-linear RGB image.
4. Create a Lum of the image and save it for future work.
5. Use the Color Mask script to create three masks in Green, Magenta and Cyan.
6. Use these color masks with Curves Transformation to bring out the colors of my RGB image as desired or shown in this attached photo (that is not mine).

But I am having trouble getting the blue and gold colors at the top and bottom ends of the image to appear as shown in in the attached thumbnail photo.
Can someone please provide me some suggestions or steps I need to follow to mimic the colors in this attached photo?

Here's the location of my three SHO files:

IC1396_Masters - Google Drive

drive.google.com

Thanks for any help, Bob

 

[pfile]

looking at your masters, there seems to be some kind of flattening issue. the edges of each image are bright as though the flats have overcorrected. this might be what's preventing you from getting correct colors.

this looks like a CMOS camera - did you use flat darks to calibrate the flats, or bias frames?

rob

 

[bmimiaga]

Rob, thanks for looking at the masters. Yes I’ve noticed the faded corners but didn’t know the cause. I have a Celestron 8” SCT with an Asi1600MM camera. I’m using an OAG and a F6.3 reducer. Will a flatter lens help in this case?
I normally crop the edges.
I created Darks, Flats and Lights and their masters using WBPP. Once the masters are cropped I can normally combine and adjust their colors but not with this image. Any suggestions? Thanks

 

[John_Gill]

With narrow-band, I would first do a stretch on each filter and then use LRGBcombination to combine the images without the L channel. Then use the Ha as the L and apply that to the newly created image. You can then run the "CorrectMagentaStars" script and then run SCNR to remove the Green which will result in the blue/gold image. By using different setting in SCNR, you can get a red/blue image.
John

 

[pfile]

Will a flatter lens help in this case?

i don't think this is necessarily an optical problem.

you shouldn't have to crop off anything more than the overlaps caused by alignment. the brightening of the corners is definitely a calibration problem.

do you only have one set of darks or do you have darks that match the flat duration?

rob

 

[fredvanner]

I'm surprised by the strong vignetting. Could you confirm that this is a Celestron 8" (e.g a C8), not an EdgeHD 8.

 

[bmimiaga]

Fredvanner - yes it's a Celestron 8" SCT, not the Edge HD 8. I assumed that some vignetting would occur because of my F6.3 reducer. I crop some of the edges and also use Automatic Background Extraction to reduce some of the vignetting.

Rob, I created a set of 40 darks at the exposure duration of my lights (300secs). The Flats are 40 sky flats created with NINA's Flat Wizard and are only a few seconds in duration.

 

[pfile]

ok, if WBPP scaled the 300s darks to match the flats then that might be a problem.

check the WBPP logs (and the control panel) to see what it did/is going to do. i think it probably makes sense to get some shorter darks to match the sky flats. with some cameras you can get away with only bias calibration of flats but that might not be the case with your camera.

rob

 

[bmimiaga]

Rob, I've added my WBPP log file onto my shared google folder where my masters are located (see the start of this thread). I don't know where to look to see if WBPP scaled my darks to the the flats.

Is this scaling problem related to my original question about not being able to bring out the image colors that I desired?
Thanks for your help!
Bob

 

[bmimiaga]

Rob, BTW I took images from three different nights and have two sets of SHO flats. I made sure the lights to flats were correctly mapped in the control panel.

 

[bmimiaga]

Rob, I think you're right about the vignetting being a flats calibration issue, not an optics issue. I've been doing some testing on my flats. After getting similar results with WBPP I manually calibrated my 40 flats and found the following; The flat on the left is a raw Ha flat, while the flat on the right was generated with the Image Calibration process. Both flats have been stretched to see the vignetting more clearly on the calibrated sub. I've also attached a copy of my ImageCalibration settings for your review. Do you see anything that might be causing this vignetting? Thanks

 

[pfile]

the problem is most likely trying to scale down 300s darks to the length of the flats. since you are trying manually, you can try two things - one would be to just uncheck the master dark in the flat calibration and calibrate the flats with only bias, make a master flat, and then calibrate your lights with that master flat (but make sure not to tick "calibrate" under the flat area when calibrating the lights. there are of course two variations there as well - either load only the master dark and turn off optimization, or load the master dark and master bias and try with optimization. if you have any amp glow at all on this sensor then you should go the route of not optimizing the dark.

the other thing you can do is get some darks that are of similar length to the flats, integrate them to make a master dark, and then calibrate the flats with only that master dark.

anyway the vignetting is totally normal, and is to be expected with almost any telescope (and doubly so for a telescope with a reducer fitted to it.) this vignetting is what you are trying to eliminate with the flats. where the flats are darker, the lights will be brightened when the light is divided by the master flat. but because there's something wrong with the flat calibration, they are over-brightening the corners in the calibrated frames.

rob

 

[bmimiaga]

the problem is most likely trying to scale down 300s darks to the length of the flats. since you are trying manually, you can try two things - one would be to just uncheck the master dark in the flat calibration and calibrate the flats with only bias, make a master flat, and then calibrate your lights with that master flat (but make sure not to tick "calibrate" under the flat area when calibrating the lights. there are of course two variations there as well - either load only the master dark and turn off optimization, or load the master dark and master bias and try with optimization. if you have any amp glow at all on this sensor then you should go the route of not optimizing the dark.

the other thing you can do is get some darks that are of similar length to the flats, integrate them to make a master dark, and then calibrate the flats with only that master dark.

anyway the vignetting is totally normal, and is to be expected with almost any telescope (and doubly so for a telescope with a reducer fitted to it.) this vignetting is what you are trying to eliminate with the flats. where the flats are darker, the lights will be brightened when the light is divided by the master flat. but because there's something wrong with the flat calibration, they are over-brightening the corners in the calibrated frames.

rob

Hi Dave,

I finally had the chance to create my Dark Flats and recalibrated and integrated my Ha Flats and Light Ha Images. It turned out much better (see attached) with no vignetting. I tried several methods but what worked for me was substituting the Bias master with the Dark Flats master. Using WBPP I couldn't find a way to add a Pedestal value but the results were good anyway.

Thanks for your help,

Bob