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What’s Wrong With My Luminance?

Processing Deep Sky
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Jim Raskett avatar
Jim Raskett avatar
I really didn’t want to post another knucklehead question, but I am not sure how to proceed.

The title says it all. I am a new mono shooter (Minicam8) and this is my first project that I included a luminance image, M33. I image in Bortle 7 skies.

I have had really nice success shooting narrowband with this camera and M33 was my first broadband project, so I am hoping that my issues are just due to inexperience. 

After a few attempts to add this L to RGB data on my own, I posted the AB thread “Adding "L" Data To RGB Data in Pixinsight”. I learned quite a bit thanks to the nice folks that responded. At the minimum, I learned how to add L to RGB at a basic level so far and plan to hone that skill.

The issue that I have with my M33 luminance (my only L so far), is that it has a nasty background and adds it to my RGB data. To me, it seems noisy and has what I would describe as a background pattern noise. I am hoping that I might be applying it incorrectly, or processing it incorrectly. I have yet to get a decent process of this data and some of the issue is the background that I believe that this L data is adding.

I am looking for comments from folks with more experience that can let me know that I have an equipment issue, or an issue with my imaging settings. Or, if this type of L result is typical. 

Here is the stretched L masterlight. It is compiled from 114 light frames of 60 seconds each. Camera is in “Linearity HDR” mode where the gain is set to 9 and the offset is 100. This mode is supposed to be for high dynamic range targets and simulates 16 bit and I have been using it quite a bit with good results (narrowband). My only other camera mode is “Full Resolution” where it shoots with a gain of 78 and offset of 50 in 12 bit. Could it be possible that imaging in Linearity HDR mode is causing my issues?



Here is a link to the masterlight on Google Drive. 

https://drive.google.com/file/d/1Jg3Nn2Dd-_lYg65R5b_vmJ50gNEE0oEW/view?usp=sharingI would really like to give M63 and M101 a try in mono and I need to get this issue resolved asap.
Thank you very much for any information, good or bad, that you can share.

Jim
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Brian Puhl avatar
Brian Puhl avatar

Have you blinked your subs? I would start there first.

I don’t believe this has anything to do with linearity HDR mode, UNLESS you switched the modes and did not update your bias frames.

Blink your stuff, look for clouds, look for registration issues. Blinking tells the story of your data. You’ll probably find it very quickly.

John Hayes avatar
John Hayes avatar

First off, I don’t see a big problem with the Lum data that I downloaded from your Google Drive. The background looks like normal photon noise and the best way to fix that is with more exposure time. 114 minutes of exposure isn’t all that much and you could improve the SNR by a factor of two if you use 4 times that much exposure, which would be in the range that I might guess you would need for this object. The good news is that you’ve got nice, round stars and pretty good looking focus so you should be able to get a good result.

John

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Jim Raskett avatar
Jim Raskett avatar
Brian Puhl:
Have you blinked your subs? I would start there first.

I don’t believe this has anything to do with linearity HDR mode, UNLESS you switched the modes and did not update your bias frames.

Blink your stuff, look for clouds, look for registration issues. Blinking tells the story of your data. You’ll probably find it very quickly.

I did blink originally but I just took another look and don't see anything out of line. A few sat trails, but that is it.
I could be using Blink incorrectly, but I normally I use it to check through the full frames for clouds, bad frames, and obvious out of whack frames. Then re-looking at a zoom level for unusual looking stars.
Overall, they do seem fairly bright though. Maybe 60 seconds is too much exposure time?

I really appreciate the suggestion Brian! I was really hoping that I missed something!
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Jim Raskett avatar
Jim Raskett avatar
John Hayes:
First off, I don’t see a big problem with the Lum data that I downloaded from your Google Drive. The background looks like normal photon noise and the best way to fix that is with more exposure time. 114 minutes of exposure isn’t all that much and you could improve the SNR by a factor of two if you use 4 times that much exposure, which would be in the range that I might guess you would need for this object. The good news is that you’ve got nice, round stars and pretty good looking focus so you should be able to get a good result.

John

Hi John,

That is excellent! More exposure time can be done certainly. 

Being my first broadband target, I really had no idea how much L, R, G, and B data I needed. I did get about 2 hours on all four channels. 

I am sure more R, G, and B would help too, but should I be capturing more luminance than each R,G, and B channels? In other words, what ratio of L should I shoot for compared to each of the R, G, and B channels?

Thanks John!
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Brian Puhl avatar
Brian Puhl avatar

Generally accepted LRGB is 3:1:1:1.

I realize now based in 60 second exposures, I think John is right. I’d maybe push it to 120, but I don’t have alot of experience imaging under skies like yours. I do know the full well should be more than capable of handling it.

Jim Raskett avatar
Jim Raskett avatar
Brian Puhl:
Generally accepted LRGB is 3:1:1:1.

I realize now based in 60 second exposures, I think John is right. I’d maybe push it to 120, but I don’t have alot of experience imaging under skies like yours. I do know the full well should be more than capable of handling it.

Much appreciated Brian!

Very good to know and thanks for that valuable information.

I imaged galaxies with my OSC camera at 60 seconds with good results (with a lp filter). I chose 60 seconds for these luminance images thinking it was a bit much. I have a lot to learn!
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John Hayes avatar
John Hayes avatar

Jim Raskett · Jan 8, 2026 at 12:18 AM

John Hayes:
First off, I don’t see a big problem with the Lum data that I downloaded from your Google Drive. The background looks like normal photon noise and the best way to fix that is with more exposure time. 114 minutes of exposure isn’t all that much and you could improve the SNR by a factor of two if you use 4 times that much exposure, which would be in the range that I might guess you would need for this object. The good news is that you’ve got nice, round stars and pretty good looking focus so you should be able to get a good result.

John


Hi John,

That is excellent! More exposure time can be done certainly. 

Being my first broadband target, I really had no idea how much L, R, G, and B data I needed. I did get about 2 hours on all four channels. 

I am sure more R, G, and B would help too, but should I be capturing more luminance than each R,G, and B channels? In other words, what ratio of L should I shoot for compared to each of the R, G, and B channels?

Remember that Lum drives the signal depth (i.e. the faintest objects you record) and determines both the image sharpness and the spatial noise in the final image; whereas, the RGB data determines the color and the color noise. So, in general, the amount of RGB data that you need is really determined by how clean you want the colors to be. For this object, my feeling is that anywhere in the range of 2-4 hours of color data for each of the RGB channels should be fine. If you can gather around double that for the Lum data (~ 4-8 hours) , you should be able to get a pretty good result. The more good data you can get, the easier it will be to process the data with regard to managing the noise. Just remember that the SNR grows as the square root of the exposure time so you quickly reach a point of diminishing returns. Double the exposure and you only gain about 40% in SNR. Quadrupling the exposure doubles the SNR, but you have to go to 16x the exposure to double it again. In the end, you always have to deal with some level of noise but it always gets easier with more exposure time.

John

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Jim Raskett avatar
Jim Raskett avatar
John Hayes:
Jim Raskett · Jan 8, 2026 at 12:18 AM
John Hayes:
First off, I don’t see a big problem with the Lum data that I downloaded from your Google Drive. The background looks like normal photon noise and the best way to fix that is with more exposure time. 114 minutes of exposure isn’t all that much and you could improve the SNR by a factor of two if you use 4 times that much exposure, which would be in the range that I might guess you would need for this object. The good news is that you’ve got nice, round stars and pretty good looking focus so you should be able to get a good result.

John

Hi John,

That is excellent! More exposure time can be done certainly. 

Being my first broadband target, I really had no idea how much L, R, G, and B data I needed. I did get about 2 hours on all four channels. 

I am sure more R, G, and B would help too, but should I be capturing more luminance than each R,G, and B channels? In other words, what ratio of L should I shoot for compared to each of the R, G, and B channels?


Remember that Lum drives the signal depth (i.e. the faintest objects you record) and determines both the image sharpness and the spatial noise in the final image; whereas, the RGB data determines the color and the color noise. So, in general, the amount of RGB data that you need is really determined by how clean you want the colors to be. For this object, my feeling is that anywhere in the range of 2-4 hours of color data for each of the RGB channels should be fine. If you can gather around double that for the Lum data (~ 4-8 hours) , you should be able to get a pretty good result. The more good data you can get, the easier it will be to process the data with regard to managing the noise. Just remember that the SNR grows as the square root of the exposure time so you quickly reach a point of diminishing returns. Double the exposure and you only gain about 40% in SNR. Quadrupling the exposure doubles the SNR, but you have to go to 16x the exposure to double it again. In the end, you always have to deal with some level of noise but it always gets easier with more exposure time.

John

Thanks John.

It is really good to hear that my main issue is as simple as time. 
I understand that more time yields diminishing returns, but the times that you are referring to are quite achievable. 

This is excellent information and I truly appreciate the help that you and Brian have given me! 

Thank you John and Brian @Brian Puhl
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John Hayes avatar
John Hayes avatar

Jim Raskett · Jan 8, 2026, 03:09 AM

It is really good to hear that my main issue is as simple as time. 
I understand that more time yields diminishing returns, but the times that you are referring to are quite achievable. 

Don’t worry Jim. You aren’t out of the woods yet! Adding more exposure time is the first step and after that, you’ll probably encounter the next hurdle. If you are going to be an astrophotographer, you have to get used to the reality that everything about this hobby is hard and just as soon as you think that you have it all figured out, something else will pop up to remind you that you should never get too complacent. It’s just the nature of the beast so just stick with it. In any event, I wish you the best of luck and I look forward to seeing the image you create from this data. I’m sure that it will be very cool.

Best regards,

John

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Jim Raskett avatar
Jim Raskett avatar
John Hayes:
Jim Raskett · Jan 8, 2026, 03:09 AM

It is really good to hear that my main issue is as simple as time. 
I understand that more time yields diminishing returns, but the times that you are referring to are quite achievable.

Don’t worry Jim. You aren’t out of the woods yet! Adding more exposure time is the first step and after that, you’ll probably encounter the next hurdle. If you are going to be an astrophotographer, you have to get used to the reality that everything about this hobby is hard and just as soon as you think that you have it all figured out, something else will pop up to remind you that you should never get too complacent. It’s just the nature of the beast so just stick with it. In any event, I wish you the best of luck and I look forward to seeing the image you create from this data. I’m sure that it will be very cool.

Best regards,

John

I got you on that John. I have been in this hobby for a short 8 years or so and have learned that it is full of challenges, but even more rewards.
I should have said that I was relieved that you feel that my main issue with the image is insufficient time. That is a hurdle that I can easily overcome!
Unfortunately, M33 has moved beyond my "window" for this time.  Hopefully I can capture more data later this year.

Thanks again John.
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Rick Krejci avatar
Rick Krejci avatar

Since the detail is coming from luminance, you can blur out the rgb data significantly before lump layering without it significantly impacting the end result. Background is especially prone to color noise. I often select the dark areas (I use Photoshop color range selection) and reduce saturation or use bxt with color noise slider very high. And if the background quality doesn’t support it, stop stretching and leave the levels lower.

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Derek Mellen avatar
Derek Mellen avatar

Are you dithering? It kinda looks like walking noise.

Jim Raskett avatar
Jim Raskett avatar
Derek Mellen:
Are you dithering? It kinda looks like walking noise.

Absolutely
Armin Lukas avatar
Armin Lukas avatar

Do you mind sharing a single sub?

Jim Raskett avatar
Jim Raskett avatar
Armin Lukas:
Do you mind sharing a single sub?

Sure. Here is one:

https://drive.google.com/file/d/10ry-783nx52Z2Me_2r-PUxh1vYBzO5wH/view?usp=sharing
Armin Lukas avatar
Armin Lukas avatar

Jim Raskett · Jan 9, 2026, 01:51 AM

Armin Lukas:
Do you mind sharing a single sub?


Sure. Here is one:

https://drive.google.com/file/d/10ry-783nx52Z2Me_2r-PUxh1vYBzO5wH/view?usp=sharing

Single frame and the master look good to me. I also think you either need longer single subs and/or more integration time.

Otherwise:

-check callibration files

-check settings in Pixinsight

Jim Raskett avatar
Jim Raskett avatar
Armin Lukas:
Jim Raskett · Jan 9, 2026, 01:51 AM
Armin Lukas:
Do you mind sharing a single sub?

Sure. Here is one:

https://drive.google.com/file/d/10ry-783nx52Z2Me_2r-PUxh1vYBzO5wH/view?usp=sharing

Single frame and the master look good to me. I also think you either need longer single subs and/or more integration time.

Otherwise:

-check callibration files

-check settings in Pixinsight

Thanks for confirming.

After John's and Brian's responses earlier in this thread, I pretty much decided that more integration time is my path forward. 

If I get fortunate enough to catch a decent night to get at least a few more hours of L on M33, I will follow up on this thread, however, clear nights are quite a rarity in my area right now. Otherwise, I will plan to collect 4-8 hours of L on my next broadband target.

Thanks Armin!
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Jim Raskett avatar
Jim Raskett avatar
Thank you all for contributing to this thread!

I have a solid plan now. Good to hear that I probably don't have equipment issues. 

Mono imaging is a fun and challenging new segment of my imaging experience and I am really getting a lot of enjoyment from it.

Even mono imaging requires a decent amount of integration time, especially in B7 skies!
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andrea tasselli avatar
andrea tasselli avatar
Jim Raskett:
If I get fortunate enough to catch a decent night to get at least a few more hours of L on M33, I will follow up on this thread, however, clear nights are quite a rarity in my area right now. Otherwise, I will plan to collect 4-8 hours of L on my next broadband target.


Think more like 30 hours, between L and RGB (in 1:1:1:1 ratio or thereabout).
Jim Raskett avatar
Jim Raskett avatar
andrea tasselli:
Jim Raskett:
If I get fortunate enough to catch a decent night to get at least a few more hours of L on M33, I will follow up on this thread, however, clear nights are quite a rarity in my area right now. Otherwise, I will plan to collect 4-8 hours of L on my next broadband target.


Think more like 30 hours, between L and RGB (in 1:1:1:1 ratio or thereabout).

Thanks Andrea, but 30 hours is completely impractical in my area. My longest integration so far is Some years, I might struggle to complete one target!
My longest integration so far I believe is M97 and it was just under 20 hours (of course it was OSC/Antlia 3nm Ha/OIII).

If that's what it takes, I will stick to narrowband, but I am going to give about 15 hours or less a shot on my next broadband target.