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Author Topic: ZERO NOISE technique  (Read 308147 times)
bjanes
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« Reply #20 on: June 25, 2007, 08:32:53 PM »
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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.

[{POST_SNAPBACK}][/a]

Despite the disclaimer regarding HDR, I'm not sure that the method is that much different from HDR, which is usually used to gain dynamic range, but can also be used to improve shadow detail as explained by Sean McHugh on his Cambridge in Colour website. See the [a href=\"http://www.cambridgeincolour.com/tutorials/high-dynamic-range.htm]Tip[/url] towards the end of the discussion.

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To do this you simply need to shoot twice making use of a tripod. One shot will be as usual, keeping highlights unburnt.

[a href=\"index.php?act=findpost&pid=124758\"][{POST_SNAPBACK}][/a]

Of course, if you are using a tripod, the first thing to try would be to shoot at base ISO and see if that gave decent shadows. If not, then the technique might be helpful, but I'm not sure if HDR techniques already available couldn't also be used.

Anyway, a good idea worth some discussion.

Bill
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Ray
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« Reply #21 on: June 25, 2007, 09:03:55 PM »
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The advantage of this method outlined by GLuijk might be the avoidance of halos around bright areas in the scene that one often gets when blending images using layer masks. I'm thinking of situations such as a bright window in a dark room. It's difficult to get an even lighting right to the edge of the window frame.

A method that replaces pixel values rather than averaging them seems likely to  solve this problem.
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Gordon Buck
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« Reply #22 on: June 25, 2007, 09:14:57 PM »
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Although I am envious of your mathematical and programming skills, I tinkered a bit with your samples and it seems to me that nearly the same effect can be obtained with CS3 HDR.  I also experimented with Photomatix (plug-in) on the CS3 HDR.

This has been a good lesson for me.  I tend to be a bit heavy handed with Photomatix and HDR (I'm probably not the only one) and this experiment has reminded me that a "non-HDR" image can be produced using the HDR process.

When the goal is a "normal" photo, the noise reduction using "HDR" is very impressive.  

I don't wish to discourage you in the development of what may very well become a new product; however, you must keep in mind that Photoshop and HDR is a competitor.

By the way, I really like the image of the junked bicycles in window light.

Thanks for stimulating a new way of thinking and processing (for me anyway).
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Guillermo Luijk
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« Reply #23 on: June 26, 2007, 01:02:54 AM »
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Hi all, you are all right: what I am doing is not far from HDR (or at least from the previous steps any HDR soft performs prior to the tone mapping stage), or to any blending technique of 2 or more images into one as CS3 can do. In fact I posted this method in the Spanish forum calling it "soft HDR". The result of combining different images will, among others, be always an increase in dynamic range through overall signal to noise ratio improvement.

What I try to show you (no commercial interest as I don't sell my little programs) is a simple soft that is focused on providing:
- Minimum noise (none of the techniques above can improve it; the more can be expected is to match results).
- Maximum texture detail in deep shadows (there is no blending in fact, just pixel selection which is optimum).
- Natural dynamic range expansion in the shadows end (not tone mapping or so steps applied than transfigure our picture's appearance and give it an unreal appearance).

The goal is provide the cleanest possible image to the user with just a click keeping the original image parameters (bright, contrast and tones). It is now up to him to choose the way how to use it; it could even be used as a free of noise input to any HDR soft (Photomatix for instance can deal with one single RAW, or you can use two versions of it for the PS HDR module), or most commonly be processed using zones without surprises when pumping up the darkest areas.

A friend of mine is modifying DCRAW's C source code to perform all these operations, not only in linear as I do, but over the RAW file itself prior to Bayer demosaicing, white balance or any scaling (in fact we are having some trouble with the black point offset most cameras keep in their RAW files that must be substracted before being able to consider a linear behaviour of the sensor, which is not strictly linear due to this offset).
And if he manages, I'll try to convince him to pursue a 16-bit DNG RAW file as an ouptput. That would be simply great, can you imagine? put a bunch of RAW files, with different arbitrary exposition, into a 16-bit RAW file free of noise ready for developing on your favourite RAW developer.
But I have a feeling that recreating the DNG RAW format is not a joke so perhaps we must be happy with just putting our fingers into the image before the developing process.
 
Regards.
« Last Edit: June 26, 2007, 01:19:56 AM by GLuijk » Logged

DiaAzul
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« Reply #24 on: June 26, 2007, 02:31:59 AM »
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Mostly with non-linear data, though, which is more unwieldy.

The best place to do most image math is in the RAW linear state where everything is very simple.
[a href=\"index.php?act=findpost&pid=124892\"][{POST_SNAPBACK}][/a]

Fair point - though I was thinking more of the HDR processing which does deal with linear data. It is much harder to blend images after they have a tone curve applied (which is what you are referring to    )
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David Plummer    http://photo.tanzo.org/
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« Reply #25 on: June 26, 2007, 05:39:28 AM »
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A friend of mine is modifying DCRAW's C source code to perform all these operations, not only in linear as I do, but over the RAW file itself prior to Bayer demosaicing, white balance or any scaling (in fact we are having some trouble with the black point offset most cameras keep in their RAW files that must be substracted before being able to consider a linear behaviour of the sensor, which is not strictly linear due to this offset).
And if he manages, I'll try to convince him to pursue a 16-bit DNG RAW file as an ouptput. That would be simply great, can you imagine? put a bunch of RAW files, with different arbitrary exposition, into a 16-bit RAW file free of noise ready for developing on your favourite RAW developer.
But I have a feeling that recreating the DNG RAW format is not a joke so perhaps we must be happy with just putting our fingers into the image before the developing process.
Regards.
[a href=\"index.php?act=findpost&pid=124921\"][{POST_SNAPBACK}][/a]

If you could manage that, than it would be gigantic. I really would love to use such a thing.  

Now if you can't do that it would use to RAW images to produce a Tiff, right ? Now do we than lose all the things from raw like whitebalance, and other adjustments ?  That would be a drawback for less noise.
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Guillermo Luijk
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« Reply #26 on: June 26, 2007, 05:50:08 AM »
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If you could manage that, than it would be gigantic. I really would love to use such a thing. 

Now if you can't do that it would use to RAW images to produce a Tiff, right ? Now do we than lose all the things from raw like whitebalance, and other adjustments ?  That would be a drawback for less noise.
[{POST_SNAPBACK}][/a]

Yes, but don't worry too much about the white balance. Firstly because the merging tool could let you set the white balance. But another option (that I really like a lot) is to develop my RAWs with DCRAW without white balance applied on them. That optimises the noise reduction algorithm as there is no pre-scaling on any of the RGB channels. If the result of the merge is a linear TIFF the white balance can easily be set with linear curves. I explain exactly this on this [a href=\"http://www.guillermoluijk.com/tutorial/dcraw/index.htm]DCRAW tutorial[/url].
David Coffin, the author of DCRAW, told me it is not recommended to develop RAW files without applying the white balance; however I have found perfect results doing it afterwards. Look at this example:

Image developed without WB:




Curves used to apply camera WB (needs the image to be a linear TIFF):




Resulting white balanced image:

« Last Edit: June 26, 2007, 05:51:13 AM by GLuijk » Logged

Gordon Buck
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« Reply #27 on: June 26, 2007, 11:00:37 AM »
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This is really interesting.

I've taken the liberty to post a few CS3 HDR edits on a temporary page of my website, see http://hornerbuck.com/reference.aspx.  

These edits were done very quickly using CS3 and the Photomatix tone map plug-in.
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mcbroomf
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« Reply #28 on: June 26, 2007, 12:09:44 PM »
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I don't profess a detailed knowledge of raw development, but isn't Tim Farrar's method the same or similar to what you propose (with a linear TIF output).  
http://www.farrarfocus.com/ffdd/bracket.htm

Mike
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Mike Broomfield
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feppe
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Oh this shows up in here!


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« Reply #29 on: June 26, 2007, 01:00:23 PM »
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This sounds intriguing. While I, too, don't see much difference in the results between this, digital blending and good HDR shots, the fact that it could be automated to a large degree would be a massive improvement over current techniques.

I do a lot of low-light photography (cityscapes mainly) and it's a major pain to get noise/fringe/halo-free images with digital blending using elaborate, blurred and manually adjusted contrast masks and blending modes. I dabbled with HDR but it's just too finicky and doesn't give me reproducible results, at least with my - admittedly limited - HDR skills.

Having a somewhat automatic but customizable program to produce expanded dynamic range images - for lack of a better term - would be heaven-sent. Please keep us posted on any updates!
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John Sheehy
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« Reply #30 on: June 26, 2007, 01:47:41 PM »
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David Coffin, the author of DCRAW, told me it is not recommended to develop RAW files without applying the white balance; however I have found perfect results doing it afterwards. Look at this example:

Image developed without WB:
[a href=\"index.php?act=findpost&pid=124943\"][{POST_SNAPBACK}][/a]

The kind of problems he is talking about probably affect mainly saturated colors of certain hues.  The RGB response of the camera is different than the RGB used in display files and mediums.  RAW converters with optimized color correction need to shift hues and vary saturation, based on hue and saturation of the white-balanced image.  If you don't WB before doing the full conversion, the wrong hues will be shifted and saturation-adjusted after white-balancing.  Some demosaicing algorithms also work with separate luminance and chroma, and these separate differently before and after white balance.
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John Sheehy
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« Reply #31 on: June 26, 2007, 01:53:32 PM »
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Having a somewhat automatic but customizable program to produce expanded dynamic range images - for lack of a better term[a href=\"index.php?act=findpost&pid=125005\"][{POST_SNAPBACK}][/a]

Better terms are definitely needed.  What most people call "HDR" is reall low, compressed DR display of a high DR scene.  Would you call AM Radio "HDR"?  No, but it is quite analogous to what is called "HDR" in digital photography.

A simple linear image with high dynamic range is really only an image with low noise in the shadows; an image in which tones are usable many stops below the maximum signal level.
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Guillermo Luijk
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« Reply #32 on: June 26, 2007, 02:29:24 PM »
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I don't profess a detailed knowledge of raw development, but isn't Tim Farrar's method the same or similar to what you propose (with a linear TIF output). 
http://www.farrarfocus.com/ffdd/bracket.htm

Mike
[a href=\"index.php?act=findpost&pid=124992\"][{POST_SNAPBACK}][/a]

yeah! It is exactly the same concept, I am glad to see someone tried it on PS. In fact in my website I pointed this:

"Another method much faster [compared to manual edition] and precise, although I ignore if possible in PS, would be to set in an upper layer the overexposed image and select on it all those individual pixels whose level in any of three channels is beyond some threshold. Done this, these pixels that would represent those burn pixels on any channel would be deleted letting see the corresponding pixels in the lower layer which would come from the correctly exposed shot"

"Otro método mucho más rápido y preciso, aunque ignoro si es realmente posible en PS, sería colocar en la capa superior la imagen sobreexpuesta corregida y seleccionar en ella todos aquellos pixels cuyo nivel en alguno de los tres canales supere cierto umbral. Hecho esto estos píxels que representarían aquellos que quemamos en algún canal, serían borrados dejando ver los píxels equivalentes de la capa inferior que corresponderían a la toma original correctamente expuesta."

I simply automated the trick so the user just needs to select the RAW files and click a button.
« Last Edit: June 26, 2007, 02:30:43 PM by GLuijk » Logged

Guillermo Luijk
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« Reply #33 on: June 26, 2007, 02:33:09 PM »
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The kind of problems he is talking about probably affect mainly saturated colors of certain hues.  The RGB response of the camera is different than the RGB used in display files and mediums.  RAW converters with optimized color correction need to shift hues and vary saturation, based on hue and saturation of the white-balanced image.  If you don't WB before doing the full conversion, the wrong hues will be shifted and saturation-adjusted after white-balancing.  Some demosaicing algorithms also work with separate luminance and chroma, and these separate differently before and after white balance.[a href=\"index.php?act=findpost&pid=125010\"][{POST_SNAPBACK}][/a]

I see, so it's a matter of correct tones achieved. Very interesting John.


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Better terms are definitely needed.  What most people call "HDR" is reall low, compressed DR display of a high DR scene.  Would you call AM Radio "HDR"?  No, but it is quite analogous to what is called "HDR" in digital photography.

A simple linear image with high dynamic range is really only an image with low noise in the shadows; an image in which tones are usable many stops below the maximum signal level.

COMPLETELY agree. The problem is that 99% of people think of HDR (which actually just means 'high dynamic range') as tone mapping. That's why I prefer not to enter this battefield and not use the HDR term.
« Last Edit: June 26, 2007, 02:34:05 PM by GLuijk » Logged

Guillermo Luijk
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« Reply #34 on: June 26, 2007, 02:38:26 PM »
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I've taken the liberty to post a few CS3 HDR edits on a temporary page of my website, see http://hornerbuck.com/reference.aspx.

Well done gordon, it's the same result. I must confess I never managed to get realistic images from Photomatix that's why I gave up. Surely the Photomatix code did the same as my routine, whenever it was possible it took noise-free pixels from the overexposed image for the ouptput.
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Wayne Fox
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« Reply #35 on: June 26, 2007, 03:27:55 PM »
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Very interesting approach ... useful on images that technically fall within the dynamic range of the sensor, but leave noise in the shadow (ie, not really HDR).

Using HDR to accomplish sounds good, but a program that actually works at the pixel level on the raw file would be a great utility.

The links in this thread have helped me understand HDR a little bit better as well.  Thanks.
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mkrupp
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« Reply #36 on: June 27, 2007, 01:23:31 PM »
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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.
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Kirk Gittings
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« Reply #37 on: June 27, 2007, 02:14:00 PM »
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I have wondered for a long time why film scanners did not use this technique to achieve extremely high dynamic range (or low shadow noise).  They clearly consider this an important specification, since they all inflate it so much in their marketing   Scanners have no stability problem, so aligning multiple exposures should be easy.  This technique would allow a scanner to deliver a merged image with full 16-bit depth, even if the sensor is capable of only 12-bit depth each pass.   Apparently a few scanners are now starting to do this ....
[a href=\"index.php?act=findpost&pid=124788\"][{POST_SNAPBACK}][/a]

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.
« Last Edit: June 27, 2007, 02:15:15 PM by Kirk Gittings » Logged

Thanks,
Kirk

Kirk Gittings
Architecture and Landscape Photography
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KenS
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« Reply #38 on: June 27, 2007, 04:03:42 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.
[{POST_SNAPBACK}][/a]


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:

[a href=\"http://tech.groups.yahoo.com/group/multipro/message/2991]http://tech.groups.yahoo.com/group/multipro/message/2991[/url]

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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Guillermo Luijk
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« Reply #39 on: June 27, 2007, 06:14:51 PM »
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2 more samples. The interest of this case is to check how the algorithm performs in presence of moving scenes (water flowing). As most of the pixels of the river were taken from the overexposed image, the result was not affected.

Real LOG histogram showing this scene was 7.5 f-stops wide. Really a hard shot as the sun was about to set so contrast was severe.




Original:




Result:

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