SharpCap Forums

Hi Robin,

Just a quick question.
Is it possible that a difference in the Banding Suppression settings between light frames and calibration frames could cause problems?
My understanding is that SharpCap’s preprocessing settings generally are not applied to the RAW files, so I assumed it wouldn’t have any effect — is that correct?
I recently captured some images where banding noise still seemed to remain even after subtracting the bias, so I’m trying to figure out what might be causing it.
Thanks in advance.

Regards,
Takuya

Hi Takuya,

if you are just capturing images in SharpCap (via start capture, etc) then the adjustments from the corrections selected in the 'preprocessing' section on the right *ARE* applied to the saved files. This is particularly designed to apply for higher speed captures - like applying flat frame correction to each frame to remove dust donuts when doing planetary/lunar imaging. However it does apply at all exposure lengths.

Conversely, if you are live stacking then the raw frames saved by live stacking *are* untouched - no preprocessing applied. The assumption here is that you would want the preprocessing steps to be applied to the images going into the stack, but to have the untouched camera raw frames for a full later reprocess.

So, given this, it's possible that your saved frames could have the banding noise correction applied to them.

If there is a difference in the application of banding noise between the dark and the light frames, *and* there is some banding that is relatively stable rather than purely random, then you could have problems... The light frames could have that banding removed, but it would still be in the dark, so it would show up when dark subtracted (in negative I think).

It might be worth running the uncorrected images through the SharpCap folder monitor camera with the banding correction turned on at the same settings. It might not be perfect, but it should help I think as then both sets of frames would have the same treatment and the subtraction should work better.

cheers,

Robin

Hi Robin,

As always, thank you for your quick and easy-to-understand response.
I see what you mean. Just to confirm—does that mean the preprocessing settings are also applied to dark frames when using the dark frame capture function?
Also, in my case, I usually create dark frames in batches using the Deep Sky Sequence Planner. In that workflow, are the preprocessing settings also applied to the RAW images?

Regards,
Takuya

Hi Takuya,

yes, in theory the preprocessing options are applied while capturing dark/flat frames too, and are included in the raw frames saved during dark/flat capture. There are some specific exclusions though:

When capturing a dark frame, existing selections for dark, flat, background subtraction, post dark flip and overexposed pixel masking are turned off during the dark capture. This avoids capturing a dark while using a dark, or a flat, etc.

When capturing a flat frame, existing selections for flat, background subtraction, post dark flip and overexposed pixel masking are turned off. Dark subtraction is left turned on (as that is one way to capture a proper flat with dark subtraction set up correctly with a dark flat file).

SharpCap restores the values of these after the dark/flat capture is completed.

cheers,

Robin

Hi Robin,

Thank you for your reply—that makes sense.

In my case, I perform live stacking as EAA while also saving the individual RAW light frames. I capture darks and flats using SharpCap’s capture tools. That might explain the discrepancy in how the Preprocessing settings were applied, which could have led to the banding not being properly removed. Given my workflow, I now realize that I should create darks and flats without applying any Preprocessing settings.

When I check the camera settings files for the individual RAW frames saved during live stacking, the Preprocessing settings are still present, making it seem like the same settings were used for the darks and flats as well.
On the other hand, I was aware that the Manual clearly states that Preprocessing settings used during live stacking are not applied to the saved RAWs. So, the Preprocessing settings in the camera settings file for the individual RAWs simply reflect the camera configuration at the time, not what was actually applied to the RAW frames—right?

Because of that, I somehow assumed that Preprocessing settings wouldn’t be applied to RAWs in other capture modes either.
I guess I should’ve read the Manual more carefully.

Anyway, it seems like I’ve identified the root cause, so I’ll try to find time to retake the calibration frames.
Thanks again for your support.

Regards,
Takuya

Hi Takuya,

that's a good point that the preprocessing settings will show in the capture settings files for live stack raw frames - I hadn't considered that, but you are quite right - what you see is the camera settings at the time and it takes no account of the fact that the frame has been saved before those preprocessing steps have been applied. I will look at correcting that.

Unfortunately with the capture dark and flat, the right thing to do depends on how you intend to use the captured dark or flat frames (ie for live stacking or not), so I can't just make SharpCap choose to do the 'right' thing in this case I have been planning to add a master on/off switch for all the preprocessing settings to easily turn them all on/off without losing the particular values. Something for SharpCap 4.2 I think

cheers,

Robin

Hi Robin,

That sounds great. I'm looking forward to it. You're absolutely right that how you use darks and flats makes all the difference.
Maybe listing clearly how the current capture settings will affect the RAW frames could help avoid confusion.

Regards,
Takuya

Hi Robin,

I set the banding suppression setting back to 0, then retook the flats and darks and applied them again.
As a result, the banding noise seems to have improved slightly, but it still cannot be completely removed.
This is probably because the position and intensity of the banding are not always stable or consistent.
If that is the case, better approach would be to apply banding removal to the lights, darks, and flats alike, and reduce the banding as much as possible before stacking.

It would be extremely helpful if an option could be added to choose whether or not preprocessing settings are applied to RAW files, not only for regular captures but also for Live Stacking.

Regards,
Takuya

Hi Takuya,

it is essential to apply the preprocessing when you are live stacking - if you do not apply dark/flat correction, hot pixel removal, etc, before adding the image to the stack then it cannot be done later to the stacked image. For example, when you add an image to the stack it is almost certainly being offset by a few pixels to align with the existing stack, and that offset will mean that attempts to use a dark or flat after stacking will not work properly.

I'm not sure about having an option to turn it off for normal captures - I have to think about what the likely outcome is across everyone who uses SharpCap - some people like you may turn it off deliberately, but what I want to avoid is creating a new way for people to do the wrong thing by turning it off by accident or just by tinkering and then forgetting it is off and getting the wrong data saved...

cheers,

Robin

Hi Robin,

I agree with you that adding a feature to turn preprocessing on and off for normal captures could introduce unnecessary risks.
If someone really wants to disable preprocessing, they can simply turn it off in the Camera Control panel (just as I did), so I feel the additional option may not be needed.

What I actually wanted to say is that it would be helpful if we could toggle preprocessing for each individual sub‑frame during live stacking.
Since banding noise does not always appear in the same location with the same intensity, when doing EAA while saving RAW sub‑frames for later post‑processing, I think it would be better not to turn off dark and flat banding suppression setting, but instead to have an option to turn on banding suppression for the light frames (the light sub‑frames for live stacking).

In my workflow, I do not use the live‑stacked RAW output for post‑processing. I always start by stacking the individual sub‑frames.
This allows me to exclude unwanted bad frames more reliably and adjust things more precisely.
For this reason, I normally never apply darks or flats during live stacking. What I mean is that applying banding suppression to the live stacking sub‑frames—using darks and flats created with the same settings—could potentially yield better results.

Sorry for the long explanation. My use case may be somewhat uncommon, but I hope my intention makes sense

Regards,
Takuya