CN says DON'T use gamma for captures

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Ben Cartwright SASS
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CN says DON'T use gamma for captures

#1

Post by Ben Cartwright SASS »


I have always used gamma on my 174mm as well as doing two captures one for the surface and one for the proms.

On cloudy nights one of the "top" solarheads says you should never use gamma and should only do a combined shot exposing for the surface and then in post you should use gamma in PS and also curves to coax out the proms since in the avi and stacked images you most likely won't see them until you work the image.

I tried his way and it is really tough to bring out the proms that are so underexposed. I personally find it a lot easier to do two captures, one for the surface and one for the proms and then process them the way I want and then combine them.

He says the gamma during capture is just software on the cameras and hurts the data and is better done in post and you can use gamma to see what it may look like but then set it back to no gamma.

I like using the gamma,

what do people think?
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Re: CN says DON'T use gamma for captures

#2

Post by Gordon »


Sometimes the 'experts' haven't used other methods. Experimenting to get the best results is the method I use.

And I agree that using your suggested method has worked better for me also!!!
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Re: CN says DON'T use gamma for captures

#3

Post by Solsearcher »


Any suggestion is worth trying out , that is how we develop our own methods . Personally I use gamma for my captures but at reduced levels for the surface , I will increase it to find the proms but then reduce it back as much as I can to reduce the sky glow . I will not usually bother with faint proms but large ones that have substance I try to not get too high on my gamma levels or it will wash out the detail I want to capture .
I have to agree , I do like my gamma , I try to use it sparingly but wouldn't want to be without it , my 2c worth .
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Re: CN says DON'T use gamma for captures

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Post by AstroBee »


Using Gamma in-camera or using adjustments in post software is still using software. It's just a matter of where it's used. In the capture or in the processing.
Do whatever works best for you.
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Re: CN says DON'T use gamma for captures

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Post by notFritzArgelander »


Gordon wrote: Mon Oct 18, 2021 6:15 pm Sometimes the 'experts' haven't used other methods. Experimenting to get the best results is the method I use.

And I agree that using your suggested method has worked better for me also!!!
An 'expert' who doesn't experiment isn't expert.
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Re: CN says DON'T use gamma for captures

#6

Post by Tillibobs »


" Expert " is derived from 2 words, " ex " meaning a has been and " spert " being a drip under pressure.
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Re: CN says DON'T use gamma for captures

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Post by Lowjiber »


Frankly, most of the solar "experts" at CN generally don't have that many decent shots when compared to either here, Solar Chat, or StarGazersLounge.

Me? I'll use gamma... Thank you very much. LOL

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Re: CN says DON'T use gamma for captures

#8

Post by FRAZ »


From a users point of view I think it depends on the software package and it is pretty impossible to use no gamma in most of them. I suspect that there is a mid range in the package of 50 out of 100 that is actually no gamma and the difference is your plus and minus.

There could be some scientific reasoning here that gives you a percentage but I have seen John use a jpeg and get better results than I can with a 16 bit image. When I grow up and be a bit more expert I might try to squeeze that fraction, until then I will go for my percentages in more tangible areas.

I do applaud that range of thinking and it blends in with what you are all saying, experiment and do what works for you.

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Re: CN says DON'T use gamma for captures

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Post by yobbo89 »


chris go says don't use gamma,it's just a software enhancment and dose nothing .. i dunno . my captures are better when i use 60-70 gamma instead of the stock 50, with 50 it seems it is alot harder to process some details as they are washed out .
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Re: CN says DON'T use gamma for captures

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Post by Lowjiber »


yobbo89 wrote: Sat Nov 06, 2021 7:24 am chris go says don't use gamma,it's just a software enhancment and dose nothing .. i dunno . my captures are better when i use 60-70 gamma instead of the stock 50, with 50 it seems it is alot harder to process some details as they are washed out .
You make a good point. It is possible to "adjust" gamma during processing, but even Photoshop can't do it as well as controlling it during the actual shoot.

I had a not-so-friendly debate with Sam Wen (ZWO chief) about gamma when he shut off gamma in SharpCap versions post-3.0. He said, "My cameras are good enough to not need gamma adjustments." That is downright stupid in my opinion. He somehow missed the point that once I purchase a camera it is mine to use as I please.

Here's what the best solar imager in the world (Alexandra Hart) had to say about using gamma control...
"Gamma control is useful in several ways but must be used with caution. Lowering the gamma will increase surface contrast and this can be an extremely useful tool in helping to achieve good focus. However it is not generally recommended to use low gamma when capturing the image. When lowering the gamma observe how the histogram shifts to the left, this will decrease the dynamic range of the blacks and ultimately lead to clipping. When this happens data is lost forever and subtle solar details within darker regions will be lost e.g. umbral structures. Surface contrast can be replicated in post-processing if you wish for it later, but if the data is lost at point of capture it can never be recovered.

Increasing the gamma will decrease surface contrast but will reveal fainter structures e.g. prominence details. Again caution must be used if capturing at a high gamma. This has a side effect by shifting the histogram to right making the blacks less black and this fogging can cause some artefacts to appear in the final image when the video is processed through the stacking program. Like before, fine structures can be revealed later in post-processing and better results can be achieved without these artefacts being in the way. With gamma, moderation is the key, there is nothing wrong with using mild increases or decreases during capture and experimentation is recommended to find what works best with your particular camera and set up. For white light imaging in general it is better to have the gamma slightly lower than neutral to enhance the granulation contrast which will aid the stacking software, for Calcium II K keep the gamma neutral or very lightly raised as the umbral detail is faint and easily can be lost altogether without caution.

Set the exposure level for surface details once gain and gamma is decided upon. Using the histogram make sure that it is around 80-90% filled, if it is over 100% then some parts of the image are over-exposed and will appear as a bright white patch containing no surface detail in the final image and structures will be lost. It is best to avoid this, but during a solar flare event it is impossible not to get a burned out region as the flare will always be off the histogram due to its huge intensity. This can add drama to the final image by showing how large and bright the flare was compared to the surrounding regions which are exposed correctly. To image prominences it may be necessary to completely over expose the solar surface to reveal the fine structures of the faint prominence."


That's been good-enough-for-me, and I'll continue to use gamma... Regardless of Wen's opinion. Avoiding clipping is a major part of my process.
John (Urban Astronomer) Apertura AD10 Dob; XLT 150 Dob; XLT 120EQ; Lunt Solar 60 PT/B1200; ES AR102; SW Pro 100ED; 2 SW Pro 80ED's; 90mm Eq; WO Z-61; SW 90mm Virtuso Mak; 2 Orion ST-80's; Quark-C; Cams: Polemaster, ASI120MM-S, ASI174MM & ASI174MM-C
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Re: CN says DON'T use gamma for captures

#11

Post by Ben Cartwright SASS »


I am probably doing it wrong to some degree, not so much with the proms but with the surface. With the proms I tend to use from 80-95 gamma depending on the proms.

with the surface I have always just cranked it down to 0 since I like the contrast but I do get some clipping in the photosphere in AR's.

there is an AR coming off the east limb and we are supposed to have some clear weather Mon and Tues, at least it is supposed to be warm up to 50 degrees F. Anyhow I will try using the histogram and not so severe gamma. I have seen if I remember when I do proms or the surface and try to get the histogram up about 80" I get a white screen totally blown out exposure but will play with it Monday
I might not always be right but I am never wrong, once I thought I was wrong, but I was mistaken...

Ferengi Rule of Acquisition #59
Free advice is seldom cheap

"Sometimes having is not so pleasing as wanting, it's not logical but it is true"
Commander Spock

Canon DSLR's R7, R6II, 5D, 7D2, 90D 21 lenses incl. 100-400L mk ii, 70-200L mk iii f/2.8, RF600/11
Lunt LS50 DS, LS80 DS, Lunt 102ED, Stellarvue SV80 APO, Orion ST80, 127 MAK, Skywatcher Evostar 120ED, 102 MAK, Celestron 8" Edge HD, 102AZ
Skywatcher EQ6-R Pro
ZWO ASI071MC-cool, ASI174mm, ASI174mm-cool, ASI178MC-cool, ASI290 mini, ASI120MM-S, ASI120MC Revolution Player One mm (178 chip)
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