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Author Topic: ZERO NOISE technique  (Read 294966 times)
EricV
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« Reply #40 on: June 27, 2007, 06:59:23 PM »
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Two points about this. First the new Silverfast does exactly this by using two scans of different exposure. BUT Sub $1000 flatbed scanners have huge stability problems and great difficulty aligning images. Because of heat expansion and cheap step motors the prosumer flatbeds have difficulty making two scans exactly the same length and there is some loss of resolution though noise is virtually iliminated.
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Good point.  With a bit more effort, though, the two exposures could be interleaved line-by-line to eliminate alignment problems.  Step to first line position, acquire scan line with short exposure, acquire scan line with long exposure, step to next line position, repeat.  At the end, you have two images with different exposure but perfect alignment, even with a poor stepper.  I don't think anybody actually does this.
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« Reply #41 on: June 28, 2007, 06:16:00 AM »
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Wouldn't it be wonderful if they could incorporate the technique right into the camera. i.e.: with one click of the shutter have the camera take two exposures, automatically adjusting the sensitivity for each, and without having the mirror move twice.
Some cameras allow exposure bracketing with mirror lock-up and a self-timer, but I'm not aware of any current cameras doing that without releasing and cocking the shutter for each exposure.

The mode you're suggesting seems to have rather few benefits over the use of multiple shutter releases.
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« Reply #42 on: June 28, 2007, 08:11:18 AM »
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Another useful technique is described here:

http://photoshopnews.com/2007/03/27/image-...p-cs3-extended/

With the Align Layer's command, you don't need a tripod (if you're careful) and once you use Median on the multiple SO, the noise is greatly reduced.
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Andrew Rodney
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jani
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« Reply #43 on: June 28, 2007, 08:56:12 AM »
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Another useful technique is described here:

http://photoshopnews.com/2007/03/27/image-...p-cs3-extended/

With the Align Layer's command, you don't need a tripod (if you're careful) and once you use Median on the multiple SO, the noise is greatly reduced.
Hmm, that seems useful, although it seems to require quite a few exposures to achieve that usefulness.

The requirement for the extended version of CS3 is also a bit bothersome; Adobe doesn't appear to provide an upgrade from CS3 to CS3 Extended.
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Jan
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« Reply #44 on: June 28, 2007, 09:00:08 AM »
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Hmm, that seems useful, although it seems to require quite a few exposures to achieve that usefulness.
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Actually in tests I did at the same exposure, the noise reduction was profound!
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Andrew Rodney
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« Reply #45 on: June 28, 2007, 09:02:32 AM »
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The requirement for the extended version of CS3 is also a bit bothersome; Adobe doesn't appear to provide an upgrade from CS3 to CS3 Extended.
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There's a back door:

[a href=\"http://photoshopnews.com/2007/05/14/bought-photoshop-but-really-want-extended/]http://photoshopnews.com/2007/05/14/bought...-want-extended/[/url]
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Andrew Rodney
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MichaelEzra
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« Reply #46 on: June 28, 2007, 09:17:38 AM »
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I am curious if the same result can be achieved in CS2 with layer blending & image calculations applied?
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larsrc
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« Reply #47 on: June 28, 2007, 09:36:06 AM »
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I have tested a technique to completely eliminate noise* on digital images based on the signal/noise ratio improvement achieved through overexposition.
At the same time this technique extremely expands the dynamic range of your image in the shadows (don't think of HDR, it's not like that) and recovers in high detail all textures present in the darkest areas of your image.
[...]
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A very interesting technique, especially for its simplicity.  Have you compared your results from those delivered by PhotoAcute (http://www.photoacute.com)?  Yes, PhotoAcute can do other things, but the noise reduction is one of the most interesting in it, and it'd be interesting to see if your method can deliver the same.

-Lars
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DiaAzul
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« Reply #48 on: June 28, 2007, 11:46:58 AM »
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A very interesting technique, especially for its simplicity.  Have you compared your results from those delivered by PhotoAcute (http://www.photoacute.com)?  Yes, PhotoAcute can do other things, but the noise reduction is one of the most interesting in it, and it'd be interesting to see if your method can deliver the same.

-Lars
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Have you got this software to work. I've downloaded the trial and thrown batches of seven bracketed Canon 1DII raw files at it without much success - gets 40 seconds into processing and crashes every time...

Looks very interesting if they can get it to work.
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David Plummer    http://photo.tanzo.org/
Guillermo Luijk
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« Reply #49 on: June 28, 2007, 12:39:54 PM »
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A very interesting technique, especially for its simplicity.  Have you compared your results from those delivered by PhotoAcute (http://www.photoacute.com)?  Yes, PhotoAcute can do other things, but the noise reduction is one of the most interesting in it, and it'd be interesting to see if your method can deliver the same.

-Lars

As you say it does a lot of things apart from noise reduction, but regarding this topic I am almost sure it cannot get the same good results as pixel selection. Think that what I do here is to take shots with a very different exposition, so the overexposed version will have much less noise (~2^4=16 times less noise with +4EV second shot) than the other. Nothing can achieve better noise reduction than JUST taking the pixels of the overexposed version whenever possible.
What PhotoAcute does is a different concept: it does not require a difference in exposition among the different shots, it just needs a lot of shots, the more the better. Through some mean or more llikely median filter it achieves noise reduction and other advantages.
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Kirk Gittings
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« Reply #50 on: June 28, 2007, 01:13:31 PM »
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I think I was pretty clear that I was not talking about dedicated film scanners. The Minolta is one of the few scanners I have not tried. What I am talking about is a mechanical issue on the flatbeds as it varies depending on the quality and age/usage of the flatbed scanner and varies tremendously depending on whether both scans are done on a warm scanner. One of the ways to defeat the problem is to do a batch scan with a couple of dummy scans up front to warm up the scanners. The latter batch scans register much better. It has become part of my workflow, when I need a high res scan, to do a warm up dummy scan first before the real multi-exposure scan on an Epson 750 or a Microtek 1800f. I have done some limited beta testing with Sf on this issue. If the scans are too far out of wack the software cannot bring it back in, but if they are a little it can handle it-hence the warm up scan. The latest version of SF has extented the "out-of-wack" parameters it can pull back in, but one must work very carefully to take advantage of it. Doing wet scans also helps with registration as there is no issue with the film changing shape from temperature differential. It is similar to having a negative "pop" from the heat as in enlarging resulting in the center of the scan being off register.

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Kirk,

I was interested in using the Silverfast S/W you refer to with my Minolta Multi Pro (non flatbed) film scanner (6x7 film) until reading about sharpness degradation due to mis-registration.  Here is a reference:

http://tech.groups.yahoo.com/group/multipro/message/2991

I know from experience that the Multi Pro hardware is capable of producing two very similar scans that can be very accurately aligned in Photoshop, so perhaps it is (or was) a Silverfast problem that prevents them from being aligned at scan time ?

Do you know if this problem has been fixed in a newer version of Silverfast?
Ken
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« Last Edit: June 28, 2007, 01:20:41 PM by Kirk Gittings » Logged

Thanks,
Kirk

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Roberto Chaves
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« Reply #51 on: June 28, 2007, 04:14:54 PM »
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Two points about this. First the new Silverfast does exactly this by using two scans of different exposure. BUT Sub $1000 flatbed scanners have huge stability problems and great difficulty aligning images. Because of heat expansion and cheap step motors the prosumer flatbeds have difficulty making two scans exactly the same length and there is some loss of resolution though noise is virtually iliminated.
[a href=\"index.php?act=findpost&pid=125218\"][{POST_SNAPBACK}][/a]

I'm thinking this should be pretty easy to solve on a cheap scanner too. Instead of using the instable step motor to do two scans one could just expose each step twice, then do a step, expose twice, do step etc...
Then the two scans would be interleaved in the same picture which is very easy to separate..
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« Reply #52 on: June 28, 2007, 04:16:31 PM »
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Good point.  With a bit more effort, though, the two exposures could be interleaved line-by-line to eliminate alignment problems.  Step to first line position, acquire scan line with short exposure, acquire scan line with long exposure, step to next line position, repeat.  At the end, you have two images with different exposure but perfect alignment, even with a poor stepper.  I don't think anybody actually does this.
[a href=\"index.php?act=findpost&pid=125296\"][{POST_SNAPBACK}][/a]

:-) I just wrote the same and now got to read your post..
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mkrupp
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« Reply #53 on: June 28, 2007, 11:29:51 PM »
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Some cameras allow exposure bracketing with mirror lock-up and a self-timer, but I'm not aware of any current cameras doing that without releasing and cocking the shutter for each exposure.

The mode you're suggesting seems to have rather few benefits over the use of multiple shutter releases.
[a href=\"index.php?act=findpost&pid=125380\"][{POST_SNAPBACK}][/a]

The bulk of this thread is about combining multiple exposures,either using PS or using the cool routine developed by GLuijk. My thought is; put the routine in the camera and let its do it all.

I was thinking along the lines of the camera taking bracketed (ISO) exposures and  doing the pixel by pixel selection and replacement using the technique decribed at the start of this thread. Only the final combined image would be saved to the memory card. Perhaps the user would set two ISO's for the exposures. One ISO gets the highlights, the other the shadows. The shutter speed and f stop would have to be the same for each exposure to avoid having wierd things happen to the combined image.

It wouldn't surprise me at all to find out this could be done with nothing more than a firmware update to the camera.
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MichaelEzra
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« Reply #54 on: June 29, 2007, 05:47:33 AM »
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Fuji S3 is doing something similar, having 2 interleaved CCD arrays of different sensitivity.
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jani
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« Reply #55 on: June 29, 2007, 01:53:55 PM »
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I was thinking along the lines of the camera taking bracketed (ISO) exposures and  doing the pixel by pixel selection and replacement using the technique decribed at the start of this thread. Only the final combined image would be saved to the memory card. Perhaps the user would set two ISO's for the exposures. One ISO gets the highlights, the other the shadows. The shutter speed and f stop would have to be the same for each exposure to avoid having wierd things happen to the combined image.
I think there will be more "weird things" happening to the combined image from ISO bracketing than shutter speed bracketing.

But yes, this could be an attractive feature to some photographers, though probably not to those who like to shoot in raw.
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« Reply #56 on: July 04, 2007, 07:25:36 AM »
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I have tested a technique to completely eliminate noise* on digital images based on the signal/noise ratio improvement achieved through overexposition.
At the same time this technique extremely expands the dynamic range of your image in the shadows (don't think of HDR, it's not like that) and recovers in high detail all textures present in the darkest areas of your image.

* It actually does not eliminate noise at all, just takes for every pixel that one with the best signal to noise ratio. That is why textures are not only 100% preserved, but improved.

To do this you simply need to shoot twice making use of a tripod. One shot will be as usual, keeping highlights unburnt. The second shot with be done with a severe overexposition (I found +4EV to be a good value). A simple piece of software merges those two shoots into one final image with no noise on it and fine detail even in the darkest zones. I have converted my modest 350D in a virtually noise-free digital camera with 12 f-stops of real usable dynamic range.

You are really reinventing the wheel here. Blending together the best parts of frames shot with different exposure levels has been around several years prior to HDR blending being added to Photoshop as a feature. I've been doing so since 2001 or so when I got my first digital camera.

Your technique can be easily duplicated in Photoshop without any special software plugins. Shoot a frame with normal ETTR technique (don't blow the highlights), and a second frame with +3 stops exposure. Process both RAWs with identical settings except for exposure, the second one processed with exposure set to 3 stops below the first. Stack the second exposure on top of the first in Photoshop, with layer blending set as follows:

[attachment=2743:attachment]

Split the two halves of the "This Layer" white slider apart by holding down the ALT key, position them as shown, and you're good to go. This will make luminance values of 220 or above come from the normal exposure, and luminance values of 35 or less to come from the +3 exposure layer. All intermediate luminance values are blended from both layers so there is a smooth transition. Setting the white blend point to 220 keeps saturated colors with clipped channels from contaminating the highlights, and seting the black blend point to 35 keeps the worst of the shadow noise from having any effect at all on the final image. Having a 185-point luminance blend range makes sure that there are no visible seams in the blended image. You can save the layer blend settings as a preset for convenient later use.

I've used this technique successfully for many years.
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jani
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« Reply #57 on: July 04, 2007, 09:10:47 AM »
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I've used this technique successfully for many years.
Unfortunately, it doesn't work well at all with the sample raw files provided by Guillermo Lujik. There are nasty highlight artifacts. Granted, the difference is 4 stops, not 3. Adjusting the sliders so that one gets rid of the highlight artifacts also seems to get rid of the reduced noise.

Care to give it a try, and compare your results with his?

Here's the post with the link to the raw files.
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Jonathan Wienke
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« Reply #58 on: July 04, 2007, 06:21:44 PM »
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Unfortunately, it doesn't work well at all with the sample raw files provided by Guillermo Lujik. There are nasty highlight artifacts. Granted, the difference is 4 stops, not 3. Adjusting the sliders so that one gets rid of the highlight artifacts also seems to get rid of the reduced noise.

The post has a link to his article, which has a link to a forum discussion with no RAW links. Post a link direct to the RAWs, so I can find them.

If you're talking about the processed JPEGS, you can't use those because they havent been equalized to matching tonal levels. For my technique to work, you must process one RAW at exposure 0 and the other at exposure -4 (if the shots were bracketed 4 stops apart), otherwise the blended result will look very weird.

The actual exposure settings don't matter, as long as they are the correct interval apart. Given a 4-stop bracket, if the normal exposure is best processed at +0.5EV in ACR, then the other RAW should be processed at -3.5EV. But if the normal exposure is best processed at +0.1EV, then the other RAW should be processed with a -3.9EV exposure setting.
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joedevico
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« Reply #59 on: July 04, 2007, 11:25:35 PM »
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The post has a link to his article, which has a link to a forum discussion with no RAW links. Post a link direct to the RAWs, so I can find them.

They're one the first page of this thread. I'm very interested to see if the same results can be achieved in Photoshop as well. I'm going to try it right now....and it does seem to do a very good job indeed!

jdv
« Last Edit: July 04, 2007, 11:36:02 PM by joedevico » Logged

Joe DeVico
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