Deep Sky Stacker Problem

[Ingo]

After stacking images in registax I get a darker final image than one of the RAW files viewed normally. Is there something I'm doing wrong? I used 26 light frames and 6 dark frames.

It's an image of M42 and I can see color in the pictures right out of the camera, but not ones that were done after stacking in registax.

:shrug:

[Zuts]

Hi,

DSS does this as well. When you save as TIFF format you are basically compressing all the brightness levels into 0 to 64k of possible brightness levels.

You need to take the registax image and adjust it in photoshop using curves followed by levels adjustment for a number of iterations to streeeettttcch out the brightness levels in the image.

If you look in the articles on this site there is a good tutorial by Eric (Ezystyles) that explains just how to do this.

Paul

[sheeny]

G'Day Ingo,

Registax is mainly designed for planetary image stacking i.e. average stacking of the images. When average stacked, the brightness of the images should not change.

For DSO's is is common to use other software like Deep Sky Stacker to sum the images. This will make the final image brighter the more subs you add (which is good to bring out faint nebula details).

It may be a silly question, but I have to ask... Are you using the "dark frames" button/checkbox to specify the dark frames or are you simply including them in the list of subs for the stack? The dark frames need to be subtracted from the lights, so you need to tell registax which files are your dark frames, and you don't include them in your stack.

When I have used dark frames in registax, I usually stack the dark frames first to average them and make a final dark frame. Then when I process the lights (subs) I tell registax to use the final dark frame.

Clear as mud?

Al.

[Ingo]

WOW! :eyepop:

I really messed up this thread :lol:

My apologies everybody, I meant Deep Sky Stacker!

:doh:

[sheeny]

:lol:... OK...:)

I'm not a DSS expert, I have used it occasionally, and it's worked OK for me.:P Best advise I can give in this case, is check your stacking options:shrug:.

:whistle:

Al.

[bojan]

The "problem" is because saved tiff picture has 16 bits, and original has only 12.
That means the saved tiff image appear darker by factor of 2^4=14x.
Just adjust curves in any photo editing software that recognises tiff format from DSS and all is OK. Do not adjust them in DSS (while this is possible, it will destroy the original data in the stacked image which is still linear.

[skwinty]

I dont use DSS, I use AIP4WIN.
I find the quoted a bit strange As:
1.AIP4WIN does not deal properly with canon 40d raw images.The opened image has severe tinges of green.
2.The canon raw is 14 bits.
3.So to get AIP4WIN to handle the image correctly, I must convert to 16 bit tiff first.
4.When AIP4WIN opens the tiff image is perfect.
5.There is a smaller bit difference of 2 bits between16, 14 and 12 bits so I dont understand why the image should be darker.
Could you elaborate on this theory please.:help:

[Zuts]

Hi,

As Bojan says, all the data is still there it is just 'hidden' in a fraction of the tiff 16 bit range. If you look at the histogram it will have a very thin base less than one tenth of the width, with complete emptiness to the left and right.

By using curves and levels you can stretch this data to occupy more of the range. By widening this histogram in an appropriate manner you can tease out all the hidden details.

Also as Bojan says, dont play around with DSS to adjust the data as basically it just destroys it. Save the image without applying the DSS default adjustments and play around in photoshop.

As I said before, Ezystyles has uploaded a howto which explains this.

Paul

[Ingo]

Thanks Everybody :thumbsup:

It's another problem though. I understand they're a lot darker when exporting them, but when it shows the preview image it's a lot lighter than the saved tiff image...BUT, it's still not showing any more compiled data than one image in the camera!

Could it be mere 4 seconds of exposures aren't going to do _anything_?

:shrug:

[Garyh]

Hi Ingo,

The slider up the top of DSS is just for gamma correction for your monitor which does help show more data, but to change the actual image to get a more unaltered image just pull all the luminance settings to zero. This should give you a totally unstretched image . But you will still have to adjust the RGB gamma slider (middle one) and probally the saturation as well. I find up the saturation to like 10-15% works well..but you will have to experiment with the RGB.
Have attached a screenprint that shows the luminance..
Oh don`t forget to check apply changes when the save dialog box comes up!
Hope this helps out as I think quiet a few people have this prob to start with.
cheers Gary

[Ingo]

Ugh. I went out again tonight and did the same session. It's a set of 60 light frames and 9 dark frames. All 60 light frames at 3.2 seconds each @ ISO1600.

I did what Garyh said to do, but didn't work again! Darn!

I used to be able to stack good and then I got the 40D and stacking started sucking. Could it be that there's a big dark lit tree in the images? :P

When I auto level it, it looks like garbage, but I did get the flame nebula, a lot of nebulosity in M42 and the running man.

[skwinty]

Hi Ingo
When you stack are you summing the images or using median or average.
for such short exposures you should be summing.

[Ingo]

I was using like..."EXTREME" on all :lol:

And sometimes average.