Onion rings

[robin]

Can anyone give me advice.Ive been imaging jupiter & when i get to the wavelets in registax & slowly adjust the bottom 3 sliders, im getting onion rings around the planets periphery. Any advice?Not enough gain?
Thanks.:help3:

[iceman]

It's typically caused by underexposure, so yes, more gain and more gamma.

For Jupiter, I use around 40-50% gain and 40-50% gamma. I get no onion rings when this happens.

As a last resort, you can do your processing in PixInSight which allows you to mask out the edge of the planet so the wavelets are only applied to the middle area.

[asimov]

I'm not convinced we've got to the bottom of this onion ring problem yet. One of my Jupiters I posted this morning was with zero gamma & zero gain. The only thing I did differently was to stack 3 filters: contrast booster/IR/UV cut/fringe killer. I was willing to go along with everyone on the conclusion that it was caused by under exposure, but now I'm unsure!

Sorry to throw the cat amongst the pidgeons here, but I'm really trying to come to a definite conclusion on these rotten onion rings.

[Robert_T]

Finally, the onion ring discussion we had to have... :P

I know Mike's convinced that this is due to under-exposure, but I have to confess to being far less sure. Really need a scientific approach trialling a wide range of settings and exposures and under different conditions to get to grips with this. It may be that under-exposure is a contributing factor, but Asi and I both think that undulating planet edge/shape due to poor seeing - when it can't be filtered out with quality (and the quality setting in registax alone can't do it), alignment box placement or culled manually, is certainly contributing.

One thing I do know is that I have Jupiter shots that Do show onion rings when they were captured with medium gain/gamma and light meter almost at the top of the K3CCD tools scale (e.g. >220), and yet others with much reduced gain/gamma settings so the light meter is reading 170-180 which Don't show onion rings? :shrug: This strongly suggests to me that exposure can only be part of the puzzle.

Anyone with clear skies often enough to run some tests :whistle:

[asimov]

I have clear skies:D I'll be trying to conduct some more tests, maybe on saturn, as it rises earlier. (I get onions on Saturn just as much as Jupiter) I will record the conditions/settings/everything/AVI taken at very little gamma/gain, & one at the 'recommended dosage' both with & without filters? Or leave the filters out of the equation? Better I leave the filters out I think.

[davidpretorius]

i do not get onion rings since having gone high gain 50% - 80% and high gamma 50%.

also i do not image is the seeing is grap ie undulating planet.

i will try will say 1/25, 1/33, 1/50 with the gain adjusted to give a similiar "brightness" on screen.

i really do have a bright image. i know with mars i was trying to underexpose, but for the last 3 months, have been pushing gamma and gain

[robin]

Thanks a lot guys for your input.Ive got clear skies tonight so I'll try a few different settings.Thing is, when Im setting the gain in K3CCD, I slide it down until i see some kind of detail on the planets disk.It just looks too bright any higher.Usually this equates to about 40-45%.Tonight I'll go higher & bump up the gamma.
By the way, had hamburgers with onions rings for tea:)

[asimov]

Lol. My wife cooks deep-fried battered onion rings on occasion...yummy!...Oops! off topic!

Now then, as I was going to say.....Davo, If I posted all my images that were NOT taken in somewhat 'crap & undulating' conditions, guess how many images I would have posted sinse owning the toucam?...TWO!

[Robert_T]

DP - do you focus at those gain levels (50-80)? It would be impossible with my setup to see anything to focus on, it would be nothing but grain.:shrug: I'm beginning to wonder if the neximage is the same as the toucam. I have imaged occasionally with gain up to 50%, but only after focussing on the planet with gain wound back...

it's complete cloud tonight as it has been for weeks, but I've decided to setup anyway and hope...

[davidpretorius]

rob,

gamma 0% to focus and then up it to 50%

[asimov]

Hmmm, it's all very interesting, isn't it? Just finished stacking an AVI of jupiter taken just after the two I posted this morning, taken at 80% gamma 55% gain {1/33 sec exposure because it was way too bright to image, normally it would be at 1/25th with less gain & gamma} complete with onion rings....

[Robert_T]

I know the feeling!:rolleyes:

[Robert_T]

thanks DP, I'll give it a try, so you don't reduce the gain to focus, just gamma?

cheers,

[davidpretorius]

correct, it seems to give enough difference to focus by.

as bird says, you can always take the gamma out later.

the gamma will help pick up any shadowy areas ie near the edges

[cometcatcher]

What's onion rings? Someone like to post a severe example?

[iceman]

robin, take note of the white level meter in K3CCD when you're about to start capturing. The image should be properly exposed, with no areas overexposed. So the white meter should be between 180-230 on most objects. I find that gives me the best range of exposure without onion rings.

Rob, as per DP, I focus with lower gain and gamma so there's higher contrast on the features to give your eyeball something to focus on. For Jupiter, I try and use a moon to focus on if the seeing is good. If the seeing is no good, it's much more difficult to focus on a dancing distorting moon.

[robin]

:shrug: That was the problem i had reconciling having my gain higher Mike.Some of the areas were overexposed so i bump the gain down which gives a nice looking, well exposed disk but then Im finding those onion rings start to rear their ugly rings from not having the gain higher.

[iceman]

Use (ie: up the) gamma in that case..

[davidpretorius]

overexposed on the screen during capture or after stackinging in registax.?

make sure histostretch is not turned on during stacking.

don't go for nice looking whilst capturing. you can have the image as grainy as hell during capture and that grain will disappear upon stacking.

here is dennis avi from that fantastic night on 4th feb. this is the first step of registax, image is very grainy and bright, but all of this can be taken out after.

in reference to this first one, where do people's capture preview screen relate? brighter, dimmer???

2nd image is the create reference on 50 of 480 frames, no wavelets. as you can see the noise has gone. no histostrech, just simple optimise / stacking.

3rd on is a finished stack of all 480 frames

4th is a finished product with rbg align and soft wavelets.


ps, dennis's data is like working with silk or viewing thru a 200mm takahashi refractor. (don't worry stu isn't imaging yet, so won't look at this thread and spam this tread with drool. no doubt he will sense that something was said in a thread, but will tear his hair out looking for it!!!)

[asimov]

Tests done last night: 9/03/06 The first image: taken using 80% gamma 55% gain & 35% brightness. 1/33rd sec exposure @ 5FPS 600 frames captured/120 stacked.

The second image: zero gamma zero gain 100% brightness. 1/25th sec exposure @ 5FPS 600 frames captured/120 stacked.

Identical heavy waveletts used on both images. Identical processing in picture publisher (unsharp mask) Identical noise reduction/sharpening in neatimage.

6" refractor & toucam. Please ignore image quality, shot in terrible seeing conditions for test purposes only.

No further tests required. :thumbsup:

[Robert_T]

I ran a heap of AVI's this morning of Jupiter. I kept the K3CCD meter generally at 215 or higher.

I used 1/20th sec exposure, gain and gamma at 50% or sometimes higher.

I have over exposure burn out and yet I have onion rings. :shrug:

At least in my case the onion rings really don't seem to be due to under-exposure. The seeing was variable.

cheers,

[Robert_T]

Just had another thought, do you think onion rings may also be exacerbated by a jittery drive? My LXD75 can sometimes run smooth as silk, but other times the image jitters around a little (more than just seeing as it stops if you tunr the drive off)????:shrug:

[davidpretorius]

i believe it is a combo of bad seeing and underexposure.

ok, i am thinking too.

double slit experiment, diffraction rings.

if we have a circular object morphing into ellipses etc with bad seeing, then as registax is in the process of beta testing multipoint alignment, then with the current version the edges of these bad circles will combine during stacking to form these onion rings like a diffraction pattern.

i have notice i still get diffraction rings when star testing even though the seeing is bad. not airy patterns, just diffraction patterns???

anyone following or am i grasping at straws

[asimov]

Yes. I get overexposure burnout & onion rings at the same time too.

As far as jittery drives go, I reckon it would depend on the frequency of the jitter.

[asimov]

I have stacked at lowest quality 95% & when reviewing the frames it has picked, a lot of my worst frames will be in there. If I let it stack all those images, I will get a crap image one way or another....That's why I ended up with RSI from hand picking frames & stacking!

[iceman]

Asi, now that's onion rings! Great test, and definitely proves the theory of underexposure. I think I deleted an image of Saturn of mine from the other week where it was very underexposed, and had obvious onion rings too.

Robert, I just want to check that you're not confusing onion rings with the "ring" that you get from oversharpening, like your far left image on your recent (great) jupiter shots.

[asimov]

Thanks Mike. I haven't finished with the testing just yet though. My intention now is to do the same test but in very good seeing conditions.

Hah! Me?....get really good seeing conditions!?? Don't be silly Asi! Stay tuned! I may get to post the test results by 2009...

[Robert_T]

might be a bit of both Mike, but I'm also definitely getting multiple onion rings lines (very fine and much fainter) further in on both sides of many of my shots... I'm thinking I've got a few issues working together. I'll try and be a bit scientific on the next run to isolate a few other variables.

cheers,

[cometcatcher]

These Onion rings look like lack of bit depth. The larger the stack the greater the bit depth. Make sure all processing steps are done in 16bpp. Only at the very last step before saving to jpeg should they be converted to 8bpp.

[Robert_T]

Asi/Guys, it's just dawned on me from Asi's test (thanks Asi) that I'm generally running brightness a lot higher (~75%), and so I'm getting burn-out before I get sufficient gain/gamma to kill the onions.... hope I have the chance to try this out tonight. Might have to eat my words :D

[asimov]

Ah..No word eating warranted. Just 'cos 99.9% of the astrophotography population told us so is no reason, lol. Besides, not sure about you, but it's in my nature to prove it for myself rather than read 'this is how it's done, just do it'.

[iceman]

I always leave brightness at default 50%

[StargazerX1]

There is plenty of evidence to suggest that other factors
may also contribute to the onion ring effect. I have experienced
this effect with properly exposed Jupiter images.

One indication that it may be a registration problem is that one can select
the Registax prefilter option (any low pass filter) in the Optimize
(not Stack) stage and they all but disappear. Unfortunately some
detail is also lost when this is done which does not appear to be recoverable in the wavelets (I use dyadic after resampling 1.7-1.8x Mitchell).

I notice this particularly when the 'good' images of the planet seem to
oscillate between an ellipsoid and a more circular shape.

If this is not the case, could it be some kind of aliasing effect from the
Bayer pattern of the color CCD? Has anybody seen these darn onion rings that are doing tri-color imaging?

Glenn
Arizona USA

[Robert_T]

Thanks Glenn, good to hear it's not just me experiencing Onioning with good exposure levels. My last two Jupiter posts on this forum being clear examples. I'll have to try the low-pass filter thingy - is there a default on Registax? Can you think of a reason that under-exposure would also contribute?

cheers,

[StargazerX1]

Robert,

The default prefilter for Registax/Optimize is off. When checked the first filter that pops up is 'flat' - same as lowpass. I found all the lowpass filters result in essentially the same result.

Underexposure certainly does limit the number of bits that will cover the limb shadows of Jupiter, perhaps gamma adjustment would correct that. With my NexImage camera I rarely get onion rings even when I expose at half saturation (128 bits) with ET 1/10s Brt 50% Sat 100% Gamma 0 (1.0) Gain 40% at F25 or so. It is with my Firewire camera (Unibrain 501c) that I get onion rings even with pels at 220.

Glenn Jolly
Celestron C11

[jmelquist]

I just did some extensive testing with IC Capture and a DFK21au04 (color) and for me on Jupiter, brightness wasn't the issue - the deciding factor was having Gamma at or above 120 resulted in onion skinning. Below is my last round of data. G=Gain (0-1024), Exp=frame exposure (seconds), Gamma (0-255), Brightness (0-63). For reference, on my system C8sct with 2.5x barlow, Exp of 1/30s and Gain of around 500 makes jupiter almost completely invisible (dark) so my tests of G=650 mad for a pretty underexposed image.

Hope this helps!!


vid044:G=650 Exp=1/30 Gamma=120 B=63 <------OnionSkin
vid045:G=1023 Exp=1/154 Gamma=100 B=63
vid046:G=1023 Exp=1/154 Gamma=100 B=0
vid047:G=1023 Exp=1/77 Gamma=100 B=0
vid048:G=1000 Exp=1/60 Gamma=100 B=0
vid049:G=1000 Exp=1/60 Gamma=100 B=63
vid050:G=840 Exp=1/30 Gamma=100 B=0
vid051:G=840 Exp=1/30 Gamma=120 B=0 <----OnionSkin
vid052:G=828 Exp=1/30 Gamma=100 B=0
vid053:G=790 Exp=1/30 Gamma=100 B=0
vid054:G=1023 Exp=1/77 Gamma=100 B=0
vid057:G=650 Exp=1/30 Gamma=120 B=0 Y800 <-----OnionSkin