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07-26-2021, 12:04 PM   #1
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Pixel Shift Question

This is probably not a very smart question, but I was wondering about the apparant number of pixels when using pixel shift. Im better at the taking pictures part than dealing with computers and printing (hopefully)...

Does the resulting file end up having the same number of pixels when looking at it on a computer even though it is larger?

My specific situation is "scanning" 4x5 film because Im to cheap/lazy to send it away for a drum scan for now. When I use pixel shift the filesize is bigger, and the detail seems clearer. I recently noticed that the editing software reads out the same number of pixels on both shifted and non shifted images despite the difference in filesize.

So should I be seeing an increase in the displayed number of pixels? If not, when it comes time to print the files should the shifted file actually print larger than the non shifted file?

I havent done large prints both ways to compare but have gotten good prints up to 20x25 using pixel shift for this. If I'm missing something and could go bigger with the same process it would be great.

07-26-2021, 01:09 PM   #2
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QuoteOriginally posted by mills Quote
So should I be seeing an increase in the displayed number of pixels?
Nope

Your camera's sensor has 36MP. Pixel shift can not change that.

PS means that your sensor/processing engine does not need to guess at the colours that it cannot record. In a normal picture your sensor records 18 million green pixels; 9 million blue and 9 million red. For the colours it cannot record it makes a guess (a very good one). In PS it does not need to guess.
07-26-2021, 01:22 PM   #3
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There are different ways Pixel Shift is implemented by different camera manufacturers. Pentax has one of the most interesting approaches - rather than generating subpixel level data and creating large increased pixel counts with interpolated data - Pentax/Ricoh went the opposite way. They reduced the uncertainty by shifting a pixel at a time to ensure that the color accuracy at a given point was not driven by as much guesswork as the normal method. (This is the primary way it works, handheld pixel shift is slightly less clear as far as how it improves accuracy). The outcome of this method is a file with higher levels of color accuracy and less noise but the same number of pixels.
07-26-2021, 01:31 PM - 1 Like   #4
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Take a look here: How Pentax Pixel Shifting Works - Articles and Tips | PentaxForums.com

And note especially this takeout: "The net result is that all 24 million pixels on the K-3 II's sensor will capture complete red, green, and blue (RBG) color data without the need for demosaicing." (hmm - note that "RBG" should be "RGB" to match the preceding text!)

So, you wind up with the same number of pixels (i.e. the image size is the same - as you note), but each of those pixels has, in some sense, more complete color information. I guess that makes the file size bigger.

07-26-2021, 01:34 PM - 1 Like   #5
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QuoteOriginally posted by mills Quote
Does the resulting file end up having the same number of pixels when looking at it on a computer even though it is larger?
My understanding is that PS files are larger because the sensor is taking 4 separate images, and embedding them all in a single RAW file. The software then combines all 4 color values (red, blue, and two green) for every individual pixel, which should generate a final jpeg of normal resolution. The final jpeg may be larger due to less compression and interpolation, but I haven't played with it enough to know.

Remember, the Pentax PS implementation isn't to increase image resolution, but to virtually eliminate noise and increase fine details by getting full color data for every pixel.
07-26-2021, 01:52 PM - 1 Like   #6
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Glad to see this question asked--and answered. Finally understand what the pixel shift is about and how it is supposed to work in the Pentaxes.
Angky.
07-26-2021, 02:53 PM   #7
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Awesome! Thanks for all the quick and thorough replies!

07-26-2021, 11:15 PM   #8
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How to handle Pentax RAW Pixelshift pictures ind Adobe Photoshop CC, to get a composed image from the 4 subimages?
07-26-2021, 11:38 PM - 1 Like   #9
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QuoteOriginally posted by joergens.mi Quote
How to handle Pentax RAW Pixelshift pictures ind Adobe Photoshop CC, to get a composed image from the 4 subimages?
Pass your DNG containing the 4 PS images to dcrawps and have it output a 16 bit TIFF, which you can then process to your heart's content with whatever you like.
It provides a lot of options, and is the simplest and quickest tool available to combine the 4 images.

Cheers,
Terry
07-27-2021, 07:02 AM   #10
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QuoteOriginally posted by tduell Quote
Pass your DNG containing the 4 PS images to dcrawps and have it output a 16 bit TIFF, which you can then process to your heart's content with whatever you like.
It provides a lot of options, and is the simplest and quickest tool available to combine the 4 images.

Cheers,
Terry
That is one solution but you could also do it in camera with RAW edit function.
07-27-2021, 08:59 PM   #11
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QuoteOriginally posted by Mikesul Quote
That is one solution but you could also do it in camera with RAW edit function.
OK.
Does that give you 16 bit tiff and also give you the raw file?

Cheers,
Terry
07-28-2021, 02:51 AM - 2 Likes   #12
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QuoteOriginally posted by tduell Quote
OK.
Does that give you 16 bit tiff and also give you the raw file?

Cheers,
Terry
I'm not sure if it is a 16 bit tiff, but you definitely can keep both the raw file and the developed tiff file.

To the OP: I think others have answered your question, but the idea with pixel shift is to give you better quality pixels, not more of them. So this is no super-resolution technique, as Olympus has. My experience says that when there is minimal movement in a scene, pixel shift gives more color depth and decreases shadow noise, such that I can push images harder without them looking pushed.

I mainly use Raw Therapee for development to a 16 bit TIFF file and then edit that in Lightroom. Lightroom is able to edit pixel shift images, but it produces artifacts everywhere where there is movement, whereas RT has a very powerful motion correction algorithm that masks in a single image's detail on areas with motion (you choose which of the 4 images the program uses). Anyway, that's what I do and it is pretty simple and fast and I use pixel shift a lot for landscape photography.
08-05-2021, 10:25 AM   #13
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QuoteOriginally posted by Rondec Quote
I'm not sure if it is a 16 bit tiff, but you definitely can keep both the raw file and the developed tiff file.

To the OP: I think others have answered your question, but the idea with pixel shift is to give you better quality pixels, not more of them. So this is no super-resolution technique, as Olympus has. My experience says that when there is minimal movement in a scene, pixel shift gives more color depth and decreases shadow noise, such that I can push images harder without them looking pushed.

I mainly use Raw Therapee for development to a 16 bit TIFF file and then edit that in Lightroom. Lightroom is able to edit pixel shift images, but it produces artifacts everywhere where there is movement, whereas RT has a very powerful motion correction algorithm that masks in a single image's detail on areas with motion (you choose which of the 4 images the program uses). Anyway, that's what I do and it is pretty simple and fast and I use pixel shift a lot for landscape photography.
...with excellent results!
08-05-2021, 01:05 PM - 1 Like   #14
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QuoteOriginally posted by GregL564 Quote
...with excellent results!
This is a thread devoted to pixel shift images... Pixel Shifted Images - PentaxForums.com
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