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03-07-2021, 07:45 PM   #1
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Misadventures in Pixel Shift: KP Edition

So I mentioned in another thread that I was so motivated to take a sky photo I almost blew off dinner with my spouse (hot pizza from take out still steaming in the box) to run outside and take some night sky shots due to a great set of clouds. I didn't, but I also didn't take long to eat. I grabbed my pizza wolfed it down, and ran to get the KP.

And here... things went downhill. I grabbed two lenses (the DA 16-50 and DA 20-40) and a tripod and a small bag - and out I went. I had all the lights outside turned off and then I got the bright idea to use Pixel Shift (with Motion correction turned off). I shot from a tripod with a 2 second self timer. But my exposures were in the range of about 10' seconds - so no SURPRISE - the sky moved. WHOOOPS!

Now I'm stuck with some photos that have stars that look like 4 small lego blocks superimposed on one another. Oy!

I normally use DXO but it sees all four images in the single DNG. I've seen a question on this not that long ago asking how to extract one image - Do I need to use the SilkyPIx software that came with the camera?


For those wanting a sneak peak - here's one of the JPGs:


I haven't got the heart to do anything with the DNG since it really does not hold up with any detailed look at the stars. And yes the sky was even better before I ate and I wish I had just done the shots normally - or maybe with Electronic Shutter only without Pixel Shift.

In any case - help!

03-07-2021, 07:54 PM   #2
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Looking closer - I'm not sure DXO is seeing the full set - perhaps the DNG's are working off only a single image. Here's another image with B&W conversion and a crop:



I still think I see stretching and problems on some of the brighter stars.
03-07-2021, 08:00 PM   #3
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Here is the same first shot from the DNG with minor tweaks and some additional DEEP PRIME noise reduction applied:

03-07-2021, 08:28 PM   #4
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I havenít done PS but I know the Pentax software will separate HDR files, I would hope it would work similarly. From an iPad that last one looks pretty good.

03-08-2021, 01:38 AM   #5
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Rawtherapee can separate out the exposures. It uses its own algorithms for motion correction too, so may be worth a try
03-08-2021, 03:54 AM   #6
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Download Raw Therapee and you can take whichever of the four exposures is best. Combining them is unlikely to work since the stars will have moved over the course of the four images.
03-08-2021, 08:53 AM - 1 Like   #7
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QuoteOriginally posted by ramseybuckeye Quote
I havenít done PS but I know the Pentax software will separate HDR files, I would hope it would work similarly. From an iPad that last one looks pretty good.
PDCU doesn't support splitting PSR files into single DNG files.

03-08-2021, 09:17 AM - 1 Like   #8
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QuoteOriginally posted by UncleVanya Quote
Looking closer - I'm not sure DXO is seeing the full set - perhaps the DNG's are working off only a single image. Here's another image with B&W conversion and a crop:



I still think I see stretching and problems on some of the brighter stars.
Like @Rondec I'd suggest using RawTherapee (available for MS Windows, MacOS and Linux).

If you want a single frame select the subframe within the Demosaicing tool of the Raw Tab. Don't set demosaicing method to Pixel Shift! Just stay with method AMAZE so changes are made only to this frame.

Check the histogram if the exposure fits. If not, skip to the Exposure Tab and adjust Exposure Compensation. If you want the biggest output color space skip to the Color Tab and change Output Profile to RTv4_Large (this is similar ProPhoto RGB).

Now you're ready to output your selected frame. Click the [Diskette symbol button] at the left of the bottom of the editor window. A dialog opens. If you want to continue work in another program I'd suggest choosing export format 16 bit tiff. Choose where to store the image, name the frame and press the [ok] button. Now continue your work within the other program. Another hint: RawTherapee doesn't support splitting into DNG single frame files.

Hope you'll get the result you're looking for - good luck!
03-08-2021, 12:02 PM   #9
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QuoteOriginally posted by acoufap Quote
Like @Rondec I'd suggest using RawTherapee (available for MS Windows, MacOS and Linux).

If you want a single frame select the subframe within the Demosaicing tool of the Raw Tab. Don't set demosaicing method to Pixel Shift! Just stay with method AMAZE so changes are made only to this frame.

Check the histogram if the exposure fits. If not, skip to the Exposure Tab and adjust Exposure Compensation. If you want the biggest output color space skip to the Color Tab and change Output Profile to RTv4_Large (this is similar ProPhoto RGB).

Now you're ready to output your selected frame. Click the [Diskette symbol button] at the left of the bottom of the editor window. A dialog opens. If you want to continue work in another program I'd suggest choosing export format 16 bit tiff. Choose where to store the image, name the frame and press the [ok] button. Now continue your work within the other program. Another hint: RawTherapee doesn't support splitting into DNG single frame files.

Hope you'll get the result you're looking for - good luck!
Thank you. Thatís very clear (I think). Iíll give it a try later in the week. I really appreciate the clear instructions.
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