Technical picture issue.

[Buldric]

I wasnt exactly sure where to put this post, but if this is a poor place for it feel more than free to move it. What this is about, is i was going over my pictures i had uploaded, and i saw something wrong with my picture of M31. Very wrong. It's appearing as circles of light around the main core of the galaxy, instead of showing the galaxy the way i edited the picture.

If anyone else is have this problem with this picture, please speak! Also speak if it looks fine, as it might be my graphics card, which could be a major problem for me, and I must know! I don't know what to do if it is the picture looking funky, if that is the case, i guess I'll first try re-uploading it, but after that... *shrug*.

Clear Skies,
Buldric

[dmill1220]

Originally Posted by Buldric

I wasnt exactly sure where to put this post, but if this is a poor place for it feel more than free to move it. What this is about, is i was going over my pictures i had uploaded, and i saw something wrong with my picture of M31. Very wrong. It's appearing as circles of light around the main core of the galaxy, instead of showing the galaxy the way i edited the picture.

If anyone else is have this problem with this picture, please speak! Also speak if it looks fine, as it might be my graphics card, which could be a major problem for me, and I must know! I don't know what to do if it is the picture looking funky, if that is the case, i guess I'll first try re-uploading it, but after that... *shrug*.

Clear Skies,
Buldric

It looks good to me!
I took the liberty to process your photo some more even though its in a jpeg format.
I used Photoshop 7.0
I adjusted the histogram settings and your dark and light points, I think your image looks very good
As a general rule aways process your images in its raw form, Ex; FIts, Raw,Tiff, do not save as a jpeg or a bitmap of gif until you have completed you post processing, this way you are not truncating down your original data, You want all the data without compression to work on before you truncate it down to a jpeg , bitmap, or Gif.

Dennis

[Buldric]

I have the original RAW as well =) I could edit the picture to look like you got it, but i thought it made it look very noisy, and grainy, almost 8-bit=p But if that looks better =p so be it! I'm still new at this, so have to learn what looks good =p

[dmill1220]

Originally Posted by Buldric

I have the original RAW as well =) I could edit the picture to look like you got it, but i thought it made it look very noisy, and grainy, almost 8-bit=p But if that looks better =p so be it! I'm still new at this, so have to learn what looks good =p

HI Buldric,

Oh No my friend! Ok, thats my fault, What I meant to say is that your inital photo looks good, When I adjusted the histogram and dark and light points I did not do a Curves or wavelet adjustment, I just wanted to see how much of the Dust lanes were still in your Jpeg data.
have you tried calibrating your screens display settings?

Dennis

[Buldric]

It only did it to me if I viewed it on this site, and only for a day, its back to normal now. However, now that I see what you were pointing out, I noticed that your version of the pic showed a LOT more dust lane than mine did, even if in not such a "pleasing" format. Is there any way I can get that out of the pic without that harsh black-white format you got it into? =p

Clear Skies,
Buldric

[Buldric]

Allright, and this is a really newbish question. I know what a "dark" is, its a picture taken with the camera shutter closed. Whats a "bias", a "flat" and an "offset" file?....

Light Frames
The Light Frames are the images that contains the real information: images of galaxies, nebula...
This is what you want to stack.

Dark Frames
The Dark Frames are used to remove the dark signal from the light frames.
With DSLRs and CCD Camera, the CMOS or CCD is generating a dark signal depending of the exposure time, temperature and ISO speed (DSLR only).
To remove the dark signal from the light frames you use a dark frame that contains only the dark signal.

The best way to create the dark frames is to shoot pictures in the dark (hence the name) by covering the lens.
The dark frames must be created with the exposure time, temperature and ISO speed of the light frames.
Since the temperature is important try to shoot dark frames at the end or during your imaging session.

Take a few of them (between 10 and 20 is usually enough). DeepSkyStacker will combine them automatically to create and use a clean master dark frame.

Bias Frames (aka Offset Frames)
The Bias/Offset Frames are used to remove the CCD or CMOS chip readout signal from the light frames.
Each CCD or CMOS chip is generating a readout signal which is a signal created by the electronic just by reading the content of the chip.

It's very easy to create bias/offset frames: just take the shortest possible exposure (it may be 1/4000s or 1/8000s depending on your camera) in the dark by covering the lens.
The bias frames must be create with the ISO speed of the light frames. The temperature is not important.

Take a few of them (between 10 and 20 is usually enough). DeepSkyStacker will combine them automatically to create and use a clean master bias/offset frame

Flat Frames
The Flat Frames are used to correct the vignetting and uneven field illumination created by dust or smudges in your optical train.

To create good flat frames it is very important to not remove your camera from your telescope before taking them (including not changing the focus).
You can use a lot of different methods (including using a flatbox) but I found that the simplest way is to put a white T shirt in front of your telescope and smooth out the folds. Then shoot something luminous (a flash, a bright white light, the sky at dawn...) and let the camera decide of the exposure time (Av mode),

The flat frames should be created with the ISO speed of the light frames. The temperature is not important.

Take a few of them (between 10 and 20 is usually enough). DeepSkyStacker will combine them automatically to create and use a clean master flat frame.

DeepSkyStacker help V2.6.3


*cough*....I see....And yet somehow I don't understand a word of it....well, a few words like "a" and "it" =p

[dmill1220]

Hi Buldric,

I dont know of many people that take Bias/Offsett frames, The only ones that I worry about are taking Darks and Flats.
When I take dark frames I always take a series of them starting with the shortest exposure that I may take on an object, all the way to the longest planned exposure, this will remove any readout noise from the CCD chip and hot pixels, Normally I take about 10 of each, starting from 1 second all the way to 45 seconds, I hardly ever go over a 45 sec sub.
IT would seem to me that a dark will eliminate the task of the Offsett / bias procedure you have quoted, that one has me intrigued???

A flat frame is very important, and is used as explained in your quoted post, the only part I dont like is the way they go about explaining how to create one.
I use the sky at twilight, you need a very even light, but not as strong as that quote says and certainly not with a towel! that will not give you an even illuminated field.
The Flat frames are averaged out to create a master flat frame.

With the darks you have to have an avg master dark for each planned exposure.
lets say for example that I plan on only Deep sky work, and I plan on only 30 second subs for the evening.
So I would take 10 or more darks at the ambient outdoor temp at the time, at 30 seconds each with my lens cap on my telescope.
while flats only need to be taken from time to time the darks must be taken before, halfway thru the night, and at the end of the night, this is only because of temperature changes.

Dennis

[dmill1220]

Originally Posted by Buldric

It only did it to me if I viewed it on this site, and only for a day, its back to normal now. However, now that I see what you were pointing out, I noticed that your version of the pic showed a LOT more dust lane than mine did, even if in not such a "pleasing" format. Is there any way I can get that out of the pic without that harsh black-white format you got it into? =p

Clear Skies,
Buldric

HI Buldric, there are several ways to extract more detail without washing out the core, one is a mix of shorter exposures along with layering techniques and a curves adjustment, the post processing is the hardest part of imaging.

Make sure your screen is calibrated properly to show all the shades of gray from black all the way to white there are web pages online that can help you in calibrating your display.
Dennis

[Buldric]

HI Buldric, there are several ways to extract more detail without washing out the core, one is a mix of shorter exposures along with layering techniques and a curves adjustment,

So basically, all I need to do is (insert random giberish that is incomprehencable), then (ditto), and then (mhmm) and I'll have a better picture! Man, thats great!

Allright, I'll admit it, I have no clue what your talking about... This pic is a stack of 30, 30 second exposures. I stick em in astro stack for a stacking technique, then randomly fiddle with the histogram (recently learned word) untill it turns out a relatively decent look for my "curves adjustment". So yea....

Clear Skies,
Buldric

[dmill1220]

Originally Posted by Buldric

So basically, all I need to do is (insert random giberish that is incomprehencable), then (ditto), and then (mhmm) and I'll have a better picture! Man, thats great!

Allright, I'll admit it, I have no clue what your talking about... This pic is a stack of 30, 30 second exposures. I stick em in astro stack for a stacking technique, then randomly fiddle with the histogram (recently learned word) untill it turns out a relatively decent look for my "curves adjustment". So yea....

Clear Skies,
Buldric

Hi Buldric,
Ok Ill try to explain it. LOL,

You can take your stack of 30 second subs since it does not wash out the core in your camera, and take exposures that are longer in duration that will show more detail in the dust lanes.

So for example lets say you take 30-30 second subs of this object and then you take multiple longer exposures of 1 minute, Now you have two stacks one at 30 seconds and one stack of 60 seconds, using layering you can do a histostretch and a curves adjustment of each stack independently of each other, to tease out as much detail as possible in each stack.

So you use the first shorter stack of 30 seconds as the first layer, then you can selectively remove the washed out core of the longer subs while still retaining the detail in the dust lanes and merge the first layer with the new longer subs with the core removed.

The result will be an image that shows the core quite well, but also the fainter dust lanes that the longer stack captures.

There are other ways to do this, you can mix up your stack with short and long exposures and use processing techniques to prevent washing out the core but still retain the outer detail of the galaxy.

Of course this is only a very simplified explanation, it's the learning of the post processing techniques that have to be mastered with the right software application.

It's way to lengthy of an explanation to post on this forum, and there are many other ways to accomplish the result that you want besides the methods I described. you will also find many different approaches on Image processing, and not all astro imagers will agree on what is best.


I suggest that you Google Layering techniques in Photo Shop, or start studying the different ways astrophotographers are using to image objects and tips on how to get the best image possible.

You have struck upon the obvious chord that astrophotography is not only a science but it's also an art form, that requires good computer skills and the mastering of several Image processing tools which by the way can be quite daunting without hands on help or a mentor.

Dennis