Heart Nebula Help

[ChrisLX200]

No way is it going to be over-exposed, but I don't think it's linear either. Nebulosity has perhaps stretched it automatically.

Rodd, if you open the stack in PixInsight - but don't do anything to it - how does it look? It should be virtually all black with maybe a few bright stars showing.

ChrisH

[Rodd]

Here's a JPEG of an HA sub (20 min) made from a raw file.  It does not get more unprocessed then this--directly from the camera

[Rodd]

It looks the same in PixS

[Davey-T]

Here's what your HA should look like straight from the camera, note difference in brightness, just stretched enough to see detail.

Rubbish image, just for comparison, same camera sensor.

Dave

Other way up to yours

[swag72]

When you say raw file - Is that the format or is the format a fit file?

Perhaps it would be more helpful if you uploaded the unprocessed fits stacks to Dropbox as there's not going to be a size issue. There's little that can be done with your jpegs and I think that people need to see the unchanged stack to try to understand what is happening - Something is happening for sure.

[ChrisLX200]

You're using Nebulosity to capture? It must be saving FIT format files - those are the unprocessed files. Something has been done to the FIT file to enable visualisation of the data - some stretching so you can see what's in there. In doing that it has (inappropriately) stretched the data blowing out the highlights. If you can, post the FIT file (or 16-bit TIF file whatever the stacking program outputs) somewhere - maybe DropBox because it will be too big to post here.

ChrisH

[johnrt]

Here is a totally unprocessed image of a section of the same nebula you are imaging from my camera, an Atik 460ex. As you can see this is very different and where you should be starting out with your raw images, the images you have posted have been stretched and altered by the software your using at some point in the process before you calibrated, stacked and combined them.

[Rodd]

No I capture using CCDops which is the SBIG camera itself.  Ha images come out at the scope looking like the one I posted.  All software just tells the camera what to do anyway--exposure time etc.  I save files to SBIG compressed--which is the recommended file for the camera.  I can also save in fits.  If I took that picture I would think the scope wasn't pointing at the right target--how can you know what the camera is pointing at if it comes out black--how can you focus? if you can't see anything.  How do you know guiding is right?

Now I am totally lost and confused.  Must step away for a awhile and regroup.  I speak regularly with SBIG--this has never come up.  

[Rodd]

Dave's unprocessed pic looks light--the one above is black---Both say its the way they should look.  

I am sure a DSLR image--or a film image would not be black.

[swag72]

John's image is absolutely bob on how stuff comes out of the CCD camera.

You say that you save as an SBIG compressed file - Perhaps this is causing issues.

I agree that it's a good stage now to take a breath and do some research. Good hunting

[Rodd]

When I get back I will try and upload the unprocessed fits stacks--but that won't help.  I already uploaded a file directly from the camera to the post--only change was from SBIG compressed to JPEG--and the SBIG compressed looks identical at the scope when the exposure time is done and the pic comes up.  I am having trouble believing that a 20 min Ha sub (or a Lum sub) at the scope is suppose to look black.  

[swag72]

When I get back I will try and upload the unprocessed fits stacks--but that won't help.  I already uploaded a file directly from the camera to the post--only change was from SBIG compressed to JPEG--and the SBIG compressed looks identical at the scope when the exposure time is done and the pic comes up.  I am having trouble believing that a 20 min Ha sub (or a Lum sub) at the scope is suppose to look black. 

So you don't believe that the image that John posted isn't what we all see when using CCD's?

Below is IC1805 - The image on the left is as it comes out of the camera - The right has had an auto stretch in PI

[Rodd]

Sara--what about Dave's file?

[ChrisLX200]

Sara--what about Dave's file?

Note Dave said 'Just stretched enough to see detail..."

[swag72]

Sara--what about Dave's file?

I'm happy to talk about my own files - See the post above yours where I have included an image - I know exactly what has and hasn't been done. 

Edit - As Chris noted Dave said that it had been minimally stretched

[Rodd]

My camera has a focus mode--takes pictures every .12 seconds so I can focus--if I could not see anything--how could I focus?

[Davey-T]

Not familiar with the SBIG software, are you saying the your downloaded image looks like the focusing one ?

A CCD  image captures all pixel values from zero to 65000 odd and the computer screen can't show these so the image from the camera will appear black and must be manipulated to reveal the relevant pixels.

Dave

Black can be stretched but white can't be unstretched

[ChrisLX200]

Look, you're getting confused about the raw data itself and what you have to do to that data in order to visualise it one-screen. Raw data is usually 16-bit (65,000 levels of grey), but the useful information is often right down at low levels - a few thousand in terms of count of grey levels. So in order to SEE what is in the raw data file you take just those few thousand levels (ignoring the rest above it) and 'stretch' that data so it occupies the full visual range. You have not affected the raw data by doing this, it's just a way of visualising it. However, if you SAVE the visualised stretched image as a 8-bit file (a jpg) then you permanently LOSE all the information that is seemingly lost in the dark areas of the raw file - the highlights are gone and cannot be recovered.

In the image below are two versions of the same image - on the left the raw file (unstretched) but on the right the same image with a temporary stretch so you can see what's in the data.

ChrisH

[Rodd]

Then how do you focus at the scope?  If you have to manipulate the image after every exposure to see if in focus you'd be there all night.  Images look black after they are calibrated maybe--That I know.  But at the scope my Ha subs look like the one I posted.  My Lum subs do to.  My RGB ones look lousy--like the ones I posted.  How do you focus?

[Barry-Wilson]

Rodd

When a FIT file downloads and is displayed on the computer screen, the Capture software produces a facsimile of the stretched image so you can see what your scope is looking at, the underlying data in the FITs file is not stretched.  It is black as you have seen in the posts above.

Processing software like PI, can also produce a facsimile of the unprocessed FITs file to show a "picture" but the underlying data is not permanently affected.  In PI you do this by using the STF and clicking the radiation symbol.  You can switch this screen stretch on and off, going from a "picture" to black.  When you apply a Histogram Transformation you permanently affect the underlying FITs file.  This is all explained in the Warrenn Keller dvds. Chris has used this STF tool in his image above.

Your SBIG ccd ought to output an unprocessed FITs file (which will be black).  On your computer screen CCDOps will be applying the facsimile of a strech to reveal the "picture" within the unprocessed black FITs file, but it is actually black.

It may be that a setting within your capture software is outputting a stretched file.  You need to investigate your settings as your unprocessed FITs file should actually be black without using the STF in PI.

Firstly, have a cup of coffee or tea and take a deep breath.  I agree that processing terminoogy can be quite confusing.  Go for a walk, whatever you need to do to clear your mind.

Then, I think you ought to check your SBIG settings so that you can output a FITs file.  This file format is the astronomical standard so your capture software must be able to do this.  Once you have a FITs file from your ccd you will be better placed to begin calibration and processing.

I seem to recall that the PI dvds had some practice FITs files, that too would be a good place to start.  You can also download files here to practice with too, http://www.mistisoftware.com/astronomy/index_fits.htm.

[Rodd]

Many thanks--now maybe I understand--the SBIG compressed format may indeed be the culprit.  Too bad it is cloudy!!!!

I appreciate all of your help--everyone.  I will also give a call to SBIG.  

Thanks

Rodd

[Davey-T]

This from Starizona guide to CCDOPS, not very clear if you need to reset something between focusing guide star and imaging but could you be capturing all your subs in focus mode ?

CCDOPS has the option to save FITS

Dave

[Davey-T]

Then how do you focus at the scope?  If you have to manipulate the image after every exposure to see if in focus you'd be there all night.  Images look black after they are calibrated maybe--That I know.  But at the scope my Ha subs look like the one I posted.  My Lum subs do to.  My RGB ones look lousy--like the ones I posted.  How do you focus?

CCDOPS also has a focusing routine where it uses a subframe to presumably give a FWHM  reading.

Dave

[Rodd]

Rodd

When a FIT file downloads and is displayed on the computer screen, the Capture software produces a facsimile of the stretched image so you can see what your scope is looking at, the underlying data in the FITs file is not stretched.  It is black as you have seen in the posts above.

Processing software like PI, can also produce a facsimile of the unprocessed FITs file to show a "picture" but the underlying data is not permanently affected.  In PI you do this by using the STF and clicking the radiation symbol.  You can switch this screen stretch on and off, going from a "picture" to black.  When you apply a Histogram Transformation you permanently affect the underlying FITs file.  This is all explained in the Warrenn Keller dvds. Chris has used this STF tool in his image above.

Your SBIG ccd ought to output an unprocessed FITs file (which will be black).  On your computer screen CCDOps will be applying the facsimile of a strech to reveal the "picture" within the unprocessed black FITs file, but it is actually black.

It may be that a setting within your capture software is outputting a stretched file.  You need to investigate your settings as your unprocessed FITs file should actually be black without using the STF in PI.

Firstly, have a cup of coffee or tea and take a deep breath.  I agree that processing terminoogy can be quite confusing.  Go for a walk, whatever you need to do to clear your mind.

Then, I think you ought to check your SBIG settings so that you can output a FITs file.  This file format is the astronomical standard so your capture software must be able to do this.  Once you have a FITs file from your ccd you will be better placed to begin calibration and processing.

I seem to recall that the PI dvds had some practice FITs files, that too would be a good place to start.  You can also download files here to practice with too, http://www.mistisoftware.com/astronomy/index_fits.htm.

 Well--I just read the CCDops manual and things are not as clear as I thought.  According to SBIG, the SBIG uncompressed as well as the

SBIG compressed do not lose any data and they recommend using these formats if file modification is intended--or to save as FITs to use with other processing software.  In either case, the image I see on the screen after the exposure time is done is the same data saved to my computer in either the SBIG or FITs formats.  They specify that the auto contrast--the stretch used to reveal the image--is not permanent and does not effect the data--so the file I call up on the computer later is the real image--WHICH DOES NOT LOOK DARK!!   SBIG is a very popular camera--how can I run  into a problem that can't be explained?  I reviewed all the files I saved and they were in the SBIG uncompressed format--which means that when I use CCDopps to open the image later--it should look dark like all of yours.  They don't.  Does anyone use SBIG products out there?  

[ChrisLX200]

Use the FITs format, even if SBIG format (which is just a container) comprises the same actual data it is the FITs format which is universal and can be loaded into any astro post-processing software. As mentioned, if the image does not look dark then you are viewing it in a temporary stretched mode, you will have little control over this stretch and it is merely done so you can get a quick view of what the data file actually contains. CCDops is doing this auto-stretch automatically for you - for convenience. This auto-stretch is certainly not a method for processing the image. You need much finer control of the stretch, and of many other factors - like noise reduction, sharpening, contrast, gradient suppression, and other things which are part and parcel of post processing an image like combining channels. You will not be able to get the best out of your data unless you work with the 16-bit raw data file so forget about jpgs, these are just used when you have a finished image and wish to post a compressed version on a forum or website etc.

ChrisH