Artefacts in long exposure astro shot, help please.

Mr Jones · 22 Dec 2009 at 22:30

Basically, I shoot in RAW, I imported, by converting all to DNG and post-processed it Lightroom. All looks fine until I export it in JPEG, no matter the resolution (250/inch, 1000px)

You guys see the artefacts around each stars?

This is straight out of camera RAW, converted to JPEG.

It looks bad on windows picture viewer but it looks worst after uploading on photobucket

Anyone know what is going on and what am I doing wrong?
No sharpening, I've turned it all down to 0 - thinking it might be the culprit.

BloodyL · 22 Dec 2009 at 22:39

Jpeg uses a sliding rule of compression ratio, evidently the ratio is too low to be able to deal with your images.
Somewhere within the Lightroom workflow will be the option to adjust your jpeg compression levels.

Kenai · 22 Dec 2009 at 22:43

At 200KB for Jpegs that size, i'd guess it's just the usual compression artifacts due to using too low a quality setting.

Mr Jones · 22 Dec 2009 at 23:34

I've got the JPEG on 100% high ????

BloodyL · 22 Dec 2009 at 23:41

Whoah!

asim18 · 22 Dec 2009 at 23:46

Omg, so many stars! I can only see ONE through my window!

All looks fine until I export it in JPEG, no matter the resolution (250/inch, 1000px)

Have you tried exporting at 100%, without any resizing?

Export one TIFF and one JPG, if the artefacts are in the JPG but not the TIFF, then it's the compression's fault.

Mr Jones · 22 Dec 2009 at 23:53

BloodyL said:
Whoah!

Indeed. It's terrible!

I've upped the resolution to 1200px, 250px/inch and saved in PNG:
Works fine, right?

Looks like I'll be going off JPEG output for shots like these then.

Mr Jones · 22 Dec 2009 at 23:56

asim18 said:
Omg, so many stars! I can only see ONE through my window!

Have you tried exporting at 100%, without any resizing?

Export one TIFF and one JPG, if the artefacts are in the JPG but not the TIFF, then it's the compression's fault.

I did that, exported it to photoshop and it was converted to TIFF, it's definitely the jpeg format, made worst by photobucket's own algorithmic.

Anyway, theses are only snap shots. I was outside my house when I decide to look up in towards the direction of the sea (Southsea, least amount of light pollution in the horizon and I literally saw 60% of these stars! *NB: the eyes could have seen more but I've been driving, headlights can be blinding)

Nutster · 22 Dec 2009 at 23:56

Is it hot pixels, that you''re just not seeing in the RAW because you're not viewing them 1:1 resolution ?

Mr Jones · 23 Dec 2009 at 00:04

Nutster said:
Is it hot pixels, that you''re just not seeing in the RAW because you're not viewing them 1:1 resolution ?

I did a 100%, I honestly thought it was hot pixels too but for a 6 second shot in -2 degrees condition, I am quite confident it's not. Here's a 100% off the top middle area where there is a cluster.

This 100% crop is saved to PNG. Saving it in jpeg gets crap like the OP.

PhillyDee · 23 Dec 2009 at 01:07

Have you tried taking dark frames? This will weed out any hot pixels / light bleed.

Oh, and a nice shot of the pleides (sp?).

You using a lens or a 'scope?
You could always ask at www.stargazerslounge.com Guarantee someone will know exactly what you need to do!

Namistai · 23 Dec 2009 at 07:53

Sorry if you've already thought about this and discounted it, but is it not just that you need to turn long exposure noise reduction on?

Mr Jones · 23 Dec 2009 at 08:50

PhillyDee said:
Have you tried taking dark frames? This will weed out any hot pixels / light bleed.

Oh, and a nice shot of the pleides (sp?).

You using a lens or a 'scope?
You could always ask at www.stargazerslounge.com Guarantee someone will know exactly what you need to do!

I'll give them a try and see if it's my hardware or just plain newbie error.
I might even actually learn what stars I've actually captured. Always fascinates me

And I was shooting with a lens. 24mm @ 35mm equiv, f2.8, 6 seconds.

Namistai said:
Sorry if you've already thought about this and discounted it, but is it not just that you need to turn long exposure noise reduction on?

I have the camera noise reduction on at standard, but shooting in RAW makes me wonder if noise could be an issue. On the .PNG converted shot, there is minimal post processed noise reduction.

Also, AFAIK, NR or not, there noise are uniform, not artefacts like that. Cheers for suggesting though, it could very well have been the culprit

jr1104 · 23 Dec 2009 at 10:42

Looks like a mixture of noise, and the compression ratio. Whenever I take star shots, I always process them and save them as TIFF files. For uploading I'll then convert it to JPEG and usually have to process it again a bit, because the conversion will have reduced the quality. This could include a bit more noise reduction, and maybe a bit of sharpening. Here's an example of what it can be like with JPEG:

PermaBanned · 23 Dec 2009 at 12:11

May i ask what exactly is wrong with the .png format? You seem disappointed that you'l have to leave JPEG behind.

Mr Jones · 23 Dec 2009 at 12:38

Superewza said:
May i ask what exactly is wrong with the .png format? You seem disappointed that you'l have to leave JPEG behind.

Nothing, just convenience from my end.
I use Lightroom 90% of my time and now with the limitation, I'm having to export it as TIFF and then convert it to .PNG from there as Lightroom doesn't do it natively. I also loose the EXIF - even though I specifically select it to store metadata.

jr1104: What's your usual workflow? RAW->TIFF->JPEG->JPEG Noise Reduced?
On another note, nice shot. What settings did you use? I might want to push for a 30second exposure next time with an ISO200.

RIZZEE · 23 Dec 2009 at 13:06

can someone explain what artefacts is please? :confused:

jr1104 · 23 Dec 2009 at 13:07

I'll usually take the RAW from the camera, and use RawTherapee and Paint.NET to convert and process it, saving it as a TIFF file for storage. If it's going on the internet, I'll usually then save a copy as a JPEG, after making any changes that I want to do for the internet version.

That shot was a 30 second exposure at ISO1600, but it was only f3.5. I'm getting a Tamron 17-50 f2.8 soon, so hopefully I can get some better shots then.

john_s · 23 Dec 2009 at 14:32

RIZZEE said:
can someone explain what artefacts is please?

A noticeable loss of quality due to the compression; for example you can often see a blocky uneven texture where there used to be a smooth, gradual transition.

There's a good (though extreme) example here:

http://en.wikipedia.org/wiki/Compression_artifact

RIZZEE · 23 Dec 2009 at 19:34

john_s said:
A noticeable loss of quality due to the compression; for example you can often see a blocky uneven texture where there used to be a smooth, gradual transition.

There's a good (though extreme) example here:

http://en.wikipedia.org/wiki/Compression_artifact

oh right, thanks!

cant see any on the stars

probably just me