Live Stack with Flat Frame Bug?

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BlackWikkett
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Re: Live Stack with Flat Frame Bug?

Post by BlackWikkett » Fri Mar 15, 2019 10:32 pm

I capture in fits format and select save exactly as seen in the drop down dialog of Live Stacking. This saves an 8 bit PNG file. Since I mainly share my images via Flickr the 8 bit format is fine for that. I capture in fits so in case I decide to capture individual frames for later processing I'll not forget to make the change to fits.

To white balance in Photoshop I use 50% gray layer with difference blending and a threshold layer to pick mid point for curves mid point. This video explains it way better than I can in a short text blurb. https://www.youtube.com/watch?v=MUh3vZT0tbo

I use an IDAS D1 light pollution filter which really steps on the red channel this is the primary reason I have to do additional white balance.

In Photoshop I usually also try noise reduction and some sharpening and saturation. I use multiple tools for this some built in and some free and paid filters and actions. For most of my images I usually spend no more than 5-10 minutes editing in Photoshop. I like the immediacy of SC Live Stacking and keeping the processing to a bare minimum.

donboy
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Re: Live Stack with Flat Frame Bug?

Post by donboy » Tue May 07, 2019 8:57 pm

admin wrote:
Tue Mar 12, 2019 10:16 pm
Hi,

My approach is to never touch the colour balance controls that come with the camera (leave them at their default settings or set them back to those if you have changed already). The problem is that for most cameras the colour balance is performed as a digital manipulation of the post ADC image data, meaning that it is somewhat destructive to image quality. I believe there are a few cameras where the colour balance controls actually are implemented through separate analogue gains for the R/G/B channels, which would be fine to use, but it is unclear which manufacturers or models work this way.

So, the goal is to do the minimum amount of manipulation of the image data prior to stacking.

With regards to flat frame and dark frame correction, all of the controls on the right-hand side with the exception of the post processing block can potentially affect the image that comes from the camera into SharpCap. Any of these that clearly make changes to the live image from the camera should be kept the same between dark frames and image frames and should only be changed cautiously between flat frames and image frames.

Cheers, Robin
That's all well and good if not using filters, but what if one uses LP filters which tend to disrupt the color balance. I've found for myself that adjusting the R & B sliders to achieve a color balance to work better. If I try and set the R & B to default (50/50) for my ASI294 then the Red slider in Live Stack doesn't have enough adjustment and when ACB for Live Stack is pressed it sends the Red slider to maximum, thus requiring the Green slider and the Blue slider to be reduced so Red channel can be balanced. And the whole ACB in Live Stack becomes a manual operation with slight loss in overall signal. Additionally, the calibration files for me work better when I use the same color balance settings as used when capturing Lights.

Don

goldtr8
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Re: Live Stack with Flat Frame Bug?

Post by goldtr8 » Sun Jun 09, 2019 12:36 pm

admin wrote:
Tue Mar 12, 2019 10:16 pm
Hi,

My approach is to never touch the colour balance controls that come with the camera (leave them at their default settings or set them back to those if you have changed already). The problem is that for most cameras the colour balance is performed as a digital manipulation of the post ADC image data, meaning that it is somewhat destructive to image quality. I believe there are a few cameras where the colour balance controls actually are implemented through separate analogue gains for the R/G/B channels, which would be fine to use, but it is unclear which manufacturers or models work this way.

So, the goal is to do the minimum amount of manipulation of the image data prior to stacking.

With regards to flat frame and dark frame correction, all of the controls on the right-hand side with the exception of the post processing block can potentially affect the image that comes from the camera into SharpCap. Any of these that clearly make changes to the live image from the camera should be kept the same between dark frames and image frames and should only be changed cautiously between flat frames and image frames.

Cheers, Robin
If you dont remember the default settings how can you reset back to the factory default. I finally understand what you mean to not modify the settings.

Thanks
Don

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Re: Live Stack with Flat Frame Bug?

Post by admin » Mon Jun 10, 2019 6:52 pm

Hi,

By default, SharpCap will reload your settings from the last time you use the camera. However by holding the control key down while the cameras opening can disable this behaviour to reset the camera to its default settings as specified by the manufacturer. See https://docs.sharpcap.co.uk/3.2/#Automa ... 20settings

Cheers, Robin

BlackWikkett
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Re: Live Stack with Flat Frame Bug?

Post by BlackWikkett » Thu Dec 19, 2019 3:09 am

Thought I was done with SharpCap Live Stacking and flat frame problems. It gives me know pleasure to bring this old thread back!

I've been unable to image for about a month and had the opportunity to get out there tonight. Of course I'd check for any updates to my favorite imaging software and apply that. Also noticed new drivers fro ZWO 3.0.0.7 so those were installed also. So now to my findings.

SharpCap v3.2.6173
Created flats with flat tool as normal, I see there is a new option to delay start for 10 seconds so I assume some changes to the flat creation tool have been made. Started live stacking and after a few images I noticed some vignetting that the flats should have taken care of. Tried to make new flats but this did not help. Here's some samples

ImageIC1396 SC v3.2.6173 Stack_15frames_450s_WithDisplayStretch by Black Wikkett, on Flickr

Uninstalled newest SharpCap and reverted back to v3.2.6128
Using the flat created in v3.2.6173 had the same issues with vignetting

ImageIC1396 SC v3.2.6128 Stack_15frames_450s_WithDisplayStretch by Black Wikkett, on Flickr

So I've gone back to v3.2.6128, removed the new ZWO driver and went beck to ZWO 3.0.0.5. drivers. Created new flat and results looked normal to me. See below.

ImageIC1396 SC v3.2.6128 with flat from 3.2.6128Stack_16frames_480s_WithDisplayStretch by Black Wikkett, on Flickr

I only have tonight for at least a week so now that I'm a working version I'm stopping the testing for now. Not sure if this is the ZWO driver or something in the newest SharpCap.

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Re: Live Stack with Flat Frame Bug?

Post by admin » Thu Dec 19, 2019 9:21 pm

Hi,

Are you using dark frames? If you are then there should be no changes to the flat frames apart from the added delay. If you're not using dark frames but you are using the option to subtract a bias frame then I made some changes to the way the offset is calculated when taking the flat frame and the flat bias frame that gave me better results. The differences should be minor unless you take your flat with a very bright illumination (bright enough for the illumination to show up in the bias frames).

Cheers, Robin

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Re: Live Stack with Flat Frame Bug?

Post by admin » Thu Dec 19, 2019 9:49 pm

Further info...

If there is a change due to the different handling of the bias frame, it will show in the naming of the flat file. When you use the bias frame option the flat file has a suffix to the file name along the lines of 'offset=1.23%'. The change only affects the calculation of this offset value which is likely to become slightly smaller if any change at all.

Cheers, Robin

BlackWikkett
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Re: Live Stack with Flat Frame Bug?

Post by BlackWikkett » Fri Dec 20, 2019 1:23 am

When creating a the flat in SC I do use the bias option also use mono for the ZWO 294 and all my OSC cameras. I've been using the same light source for making the flat for months. It's a tracing tablet set to the lowest output then diffused through two layers of T-shirt. I setup 300 gain and set exposure to about 215 - 220 ms and use 50 subs to create the master flat. I have the smart histogram open and try to get the lum channel (white in the histogram) peak to about 50% and make sure the highest channel in my case green is not saturated.

You'll have to explain the part about the the light source brightness. My thinking is if the light source is dimmer then I'll be increasing the exp or gain to get the correct histogram.

I'm one user that was quite happy with the way the flat process worked before the change. I'm sure there was a good reason to make the change. I'd ask if there would be a way to allow for the old and new way to coexist in future version. As it is now i'm stuck at v3.2.6128 since that works best for me.

Thanks for your attn, Chris

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Re: Live Stack with Flat Frame Bug?

Post by admin » Fri Dec 20, 2019 2:10 pm

Hi Chris,

So the exact changes I made to the flat frame creation were

1) capture the bias frame at a shorter exposure – previously 1 ms was used for the bias frame, now 10 times the camera minimum exposure is used if that is less than 1 ms.

2) extrapolate the offset value recorded in the saved flat file name down to the predicted offset for a zero time exposure rather than using the mean bias frame brightness.

The net result of these is that the offset percentage recorded in the filename may be slightly lower with the new version, which should properly represent the background brightness in a zero exposure dark frame and (previously it would be the average brightness of the 1 ms bias frame). This should give better flat frame correction for short light exposures (where you are not using a dark frame). If you do use a dark frame then the chain should have no effect.

Please can you look at the file names of your two different flats created with the different version to see if the offset percentage has indeed been reduced and by how much. Also, what exposure light frames are you using, and are you using a dark frame?

Thanks, Robin

BlackWikkett
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Re: Live Stack with Flat Frame Bug?

Post by BlackWikkett » Sat Dec 21, 2019 1:23 am

v3.2.6173 flat file name 19_17_06_offset=0.005%.fits

v3.2.6128 flat file name 21_14_17_offset=0.243%.fits

For light frames I'm using 30 seconds 300 gain and using dark frame along with the flat.

Creating the flat I don't use dark frames using the bias function instead.

-Chris

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