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08-01-2017, 12:00 AM - 5 Likes   #1
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Composition Adjustment and Noise Reduction

For anyone who shoots multiple images for stacking in what ever situation (astronomy, low light landscapes, etc.), using Composition Adjustment may be of benefit in terms of reducing noise. The technique is usually referred to as "dithering". Here is a definition....
In astrophotography, to dither means to shift the pointing of the telescope slightly in random directions between exposures. This allows hot and cold pixels, cosmic ray artifacts, and fixed pattern noise, and even satellite or airplane trails to be removed during the stacking process.
Here are a couple of article on the approach - using astronomy as an example.For shooting landscapes, in particular at night where you want to reduce fixed pattern noise, and you are planning to shoot multiple frames for stacking, you can employ the Composition Adjustment (CA) capability to slightly move the sensor between each image. On the K1, each CA unit adjustment is about 10 pixels. To start to negate fixed pattern noise, a random movement of about 10 -12 pixels is usually sufficient. After taking your images, the stacking software usually aligns the images, there by each frame would have a slightly different fixed pattern noise that would start to cancel out when stacked. Now, since Pentax is the only body that provides this capability, Composition Adjustment is not reflected in this following article, but it would enhance the results.I know that the K5, K5II, K5IIs, K3, K3II and K1 has Composition Adjustment. I suspect that other bodies has it as well - probably the K70 and KP. As to the others - I have not checked.

It would be nice for Pentax to automate this in firmware to provide a small random movement from frame to frame - when the capability is enabled.
_______________________

Note - there is more on this concept over at another post...



Last edited by interested_observer; 08-01-2017 at 07:16 AM.
08-01-2017, 02:48 AM   #2
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Although my experience in astrophotography, apart from occasional shots of the moon, is next to zero, this still sounds like an interesting and constructive feature suggestion to me. Also one that should be fairly easy to implement.
08-01-2017, 03:34 AM   #3
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I think that even taking multiple shots without moving the frame has NR benefits if stacked. Would be interesting to compare that with this approach.

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08-01-2017, 07:14 AM   #4
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A few more thoughts....

This concept of using Composition Adjustment to provide additional Noise Reduction - is extremely simple to implement - essentially it is already been done. It is essentially Pixel Shift with an extension - but rather than shifted one pixel (for a shift in RGB), you would shift say 11 pixels. I'm pegging 11 pixels, because 10 pixels should be a sufficient amount of movement to get negate fixed pattern noise and one additional pixel in order to move to an adjacent RGB pixel. So this would approach a) negate fixed pattern noise and b) pickup the additional color information from the Pixel Shift concept. Automated, you could easily pre-program an 9 shot pattern with out repeating. With this, you would essentially loose an 11 pixel frame around the entire image, but that would be a very small price to pay for the additional benefits.

This could be easily implemented and retrofitted in a firmware upgrade, across the units - even going back to the K5. If an 11 pixel movement is too precise for the older units, then use a value that they are capable of handling. If automated, I believe that the folks in the Astrophotography social group - in particular Pete-XL, StoneG and company could find it useful. The deep space object images that they are producing are just absolutely stunning.



08-01-2017, 07:31 AM   #5
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Interesting. I think it's more practical for landscapes than for astrophotography. Thoughts on astro follow.

If you are using the astrotracer and taking multiple shots, you already get dithering because your target starts in a different spot with each exposure.

If you are using a mechanical tracking mount (one of the small sky trackers or a German Equatorial Mount) without autoguiding, you will get some drift dithering unless you have perfect polar alignment.

Finally, if you use a mechanical mount with autoguiding, then you could theoretically benefit from composition adjust dithering, but it may be easier to just set your autoguiding software to do the dithering. Pressing camera buttons to activate composition adjust between exposures risks shaking the camera and disrupting autoguiding. I don't think tethering allows access to composition adjustment - corrections welcome.

I wrote that before seeing your 2nd post. An automated exposure sequence shifting by 11 pixels would work with autoguiding]

Last edited by DeadJohn; 08-01-2017 at 07:37 AM.
08-01-2017, 08:19 AM   #6
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I do agree with you. The manual approach could be just too time consuming, and if you are putting the entire setup in to automatic and going inside, then it's a moot point. The only approach that makes sense is for Pentax to automate it - but who knows what Pentax will actually do.

It would be really nice if Pentax were to just open up the USB with a full API and let third party developers go to town. BackyardEOS and Nikon are a good example of this (but offers dithering at the mount).

Landscapes could benefit and shooting in sets of 4 images, this could be reasonably easy. Actually, that's where I got the idea in terms of eliminating noise from very low ISO single shots of some night landscape because the Milky Way was clouded in. I like to do the MW over some interesting landscapes.

08-01-2017, 09:30 AM   #7
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Seems like one simply allow the night sky to shift between exposures, maybe wait a minute or so between shots, depending on focal length. Applicable for shots of night sky only, not for shots including fixed landscape.
11-22-2017, 01:15 PM   #8
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QuoteOriginally posted by interested_observer Quote
A few more thoughts....

This concept of using Composition Adjustment to provide additional Noise Reduction - is extremely simple to implement - essentially it is already been done. It is essentially Pixel Shift with an extension - but rather than shifted one pixel (for a shift in RGB), you would shift say 11 pixels. I'm pegging 11 pixels, because 10 pixels should be a sufficient amount of movement to get negate fixed pattern noise and one additional pixel in order to move to an adjacent RGB pixel. So this would approach a) negate fixed pattern noise and b) pickup the additional color information from the Pixel Shift concept. Automated, you could easily pre-program an 9 shot pattern with out repeating. With this, you would essentially loose an 11 pixel frame around the entire image, but that would be a very small price to pay for the additional benefits.

This could be easily implemented and retrofitted in a firmware upgrade, across the units - even going back to the K5. If an 11 pixel movement is too precise for the older units, then use a value that they are capable of handling. If automated, I believe that the folks in the Astrophotography social group - in particular Pete-XL, StoneG and company could find it useful. The deep space object images that they are producing are just absolutely stunning.

Hi observer, i'm very interested about this possibility. I think that even the K-5 has the hardware capability to manage the sensor in order to properly expose every RGB color and get full colour information for every pixel. Of course i don't think that Pentax has interest to retro-support this feature on older models.
I think that praticing the composition adjustment way is the only chance to achieve this.
Now, the side of a single pixel in this sensor is about 4.8m (height of the pixel=height of the sensor/pixels of the short side=15.6mm/3264; width of the pixel=width of the sensor/pixels of the long side=23.6mm/4928). The composition adjustment shifts the sensor for a maximum of 1,4mm on each direction; it has 24 steps. This means that every step shifts the sensor of 0,06mm, or 60m, so 12,5 pixels. To reach a full number, two steps mean 25 pixels, and as long it is an odd number, this will work to reach every RGB color. With a loss of -i guess- about less than half-million pixels, we can achieve the sharpness and the level of details of a Foveon sensor, even if there's no place for motion in the scene.
Every information or contribute about this project will be helpful!

And...sorry for my english, of course

11-22-2017, 01:40 PM   #9
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Does this mean (in a nutshell), use the in-camera composition adjustment feature for each shot then just stack them !?
In my case, that would be the K3.
Thanks.
11-22-2017, 02:11 PM   #10
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The technique of photo stacking is another thing. We are discussing about the pixel shifting! Trying to emulate the apposite feature of the K-3II and K-1
11-24-2017, 11:39 PM - 1 Like   #11
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QuoteOriginally posted by zen39 Quote
Hi observer, i'm very interested about this possibility. I think that even the K-5 has the hardware capability to manage the sensor in order to properly expose every RGB color and get full colour information for every pixel. Of course i don't think that Pentax has interest to retro-support this feature on older models.
I think that praticing the composition adjustment way is the only chance to achieve this.
Now, the side of a single pixel in this sensor is about 4.8m (height of the pixel=height of the sensor/pixels of the short side=15.6mm/3264; width of the pixel=width of the sensor/pixels of the long side=23.6mm/4928). The composition adjustment shifts the sensor for a maximum of 1,4mm on each direction; it has 24 steps. This means that every step shifts the sensor of 0,06mm, or 60m, so 12,5 pixels. To reach a full number, two steps mean 25 pixels, and as long it is an odd number, this will work to reach every RGB color. With a loss of -i guess- about less than half-million pixels, we can achieve the sharpness and the level of details of a Foveon sensor, even if there's no place for motion in the scene.
Every information or contribute about this project will be helpful!

And...sorry for my english, of course
QuoteOriginally posted by jpzk Quote
Does this mean (in a nutshell), use the in-camera composition adjustment feature for each shot then just stack them !?
In my case, that would be the K3.
Thanks.
QuoteOriginally posted by zen39 Quote
The technique of photo stacking is another thing. We are discussing about the pixel shifting! Trying to emulate the apposite feature of the K-3II and K-1
Overall, where I was trying to go is that on the sensor, the noise is going to manifest itself slightly differently from area to area. So, my thinking is that with Pentax's ability to shift the sensor around, you can take several images, shifting the sensor in varying amounts and varying directions. Then with stacking the noise in each individual image when summed together will be slightly different, and thus be canceled out more effectively. This is a technique done in astro photography that is called dithering.

It is a form of pixel shifting - but shifting say 10 to 15 pixels at a time - from image to image, which would essentially be around one increment in terms of Composition Adjustment.

12-13-2017, 04:00 AM - 1 Like   #12
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The most efficient way of removing fixed pattern noise (and easiest to do it) is to use dark frame subtraction.
Dark-frame subtraction - Wikipedia
Most cameras can apply this automatically (on long exposure shots)

Using composition adjust will subtract fixed pattern noise too, but not as efficient as DFS. And as fixed pattern noise is usually the same, you can reuse DFS shots you already captured if doing it manually. Unless you want to achieve something else than removing fixed patter noise, using composition adjustment seems to add more complexity than necessary.

Stacking image is more efficient on removing random noise. But if FI shooting 4 shots and stacking them to reduce noise, you will basically get the same noise level as if using 4 times as long single exposure using 2 stops lower ISO. As long as the total exposure time is the same (same amount of light captured) it should not make much difference in random noise between stacking or single exposure. Long exposure may increase fixed patter noise because of heat in the sensor, so if you can wait for the sensor to cool down between stacking shots this noise may be lowered by using stacking.

Depending on the application one method may be better than the other.
Stacking also gives the advantage of removing part of the exposure if something goes wrong. Which can be an advantage if using very long exposures.
For astrophotography you may also want to use stacking (unless you have astrotracer) to avoid star trails.
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