[Robert S Donovan]

I love shooting long exposures at night with my K10D. However, I hate the 1:1 dark frame subtraction second exposure the default long exposure noise reduction setting requires. I discovered if you shoot RAW you can disable the noise reduction feature in long exposure shots and your RAW software will take care of any hot pixels for you. This makes shooting long exposures much more tolerable.

Check out my blog article with samples.

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Last edited by Robert S Donovan; 05-02-2009 at 10:01 AM. Reason: updated URL

[roentarre]

Moved to dSLR section.

[Robert S Donovan]

Moved to dSLR section.

Thanks. I wasn't sure...

[LeoTaylor]

There is Noise and there is Noise. I’m no expert, but I’ve done a lot of astrophotography where background noise from the CCD sensor is a major problem.

Your examples appear to show you are looking at noise in the subject. This is mainly affected by ISO and light level. The thermal noise caused by the sensor shows mainly in a dark background. One hopes that the subject is brighter than the noise and if the whole frame is bright then perhaps you can skip the Noise Reduction.

Below are some astrophotos taken with a K110D for demonstration. All are 60 second RAW exposures. The first is with the camera Noise Reduction disabled. Note the multicolor speckles in the dark sky. This is the noise NR is designed to reduce. This noise would be difficult to repair afterward since it resembles the desired stars. The second photo has NR enabled. Note the speckles are substantially reduced. The third photo is actually the same frame as the first with a dark frame subtracted afterward. In other words, I took a third 60 second frame last night with the telescope capped and this morning subtracted the dark frame from the first light frame. This is done by astrophotographers who want to take the light frames as fast as practical and handle the dark subtraction later.

Attached Images

     

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Last edited by LeoTaylor; 03-26-2009 at 09:59 AM. Reason: Added word

[WMBP]

Robert,

On your blog you say:

From what I could tell from this test, there is virtually no difference in noise between the RAW images with and without in-camera noise reduction. In fact, to me the images without the NR has slightly better contrast and more shadow detail. Keep in mind that these are unprocessed RAW files so I could easily get similar contrast and saturation as the JPEG image while maintaining the greater detail and dynamic range of the RAW images.

Your first sentence (very little difference in raw images with or without in-camera noise reduction) jives with my own experience. But that makes sense, no? I am not sure about this but I would not expect an in-camera setting for noise reduction to affect the raw file any more than the settings for sharpness and contrast do. The raw file contains the raw data, end of story. Would love to know if I'm wrong, but I'd be disappointed if the raw file was anything other than what the name implies - a raw capture data file.

I assume that the in-camera noise reduction option is still there because many photographers still allow the camera to convert the raw capture to jpeg. I tend to keep the setting in my K20D at "low" noise reduction and beyond that, I seldom think about it.

Small quibble: You can't really post - or for that matter, view - unprocessed raw files. Simply viewing the file for the first time in Photoshop or Lightroom or Aperture, Bibble, SilkyPix, LightZone or Picasa, involves some processing of the raw data. That's what accounts for the observation that raw files look a bit different initially in different programs. I take it that what you mean by "unprocessed" is that you didn't apply any special processing, like noise-reduction in Noise Ninja, that sort of thing.

Will

[LeoTaylor]

The raw file contains the raw data, end of story. Would love to know if I'm wrong, but I'd be disappointed if the raw file was anything other than what the name implies - a raw capture data file.

I'm sorry to disappoint you but I use Noise Reduction with RAW format often, about as often as I turn it off. NR is an explicit option in the Custom Setting menu. I'd be disappointed if I could NOT enjoy reduced thermal noise when I chose to use RAW.

Last night I took 51 one minute RAW images of some galaxies. It took 115 minutes because I chose to use NR and a 15 second delay between images.

[WMBP]

I'm sorry to disappoint you but I use Noise Reduction with RAW format often, about as often as I turn it off. NR is an explicit option in the Custom Setting menu. I'd be disappointed if I could NOT enjoy reduced thermal noise when I chose to use RAW.

Leo,

There are two noise reduction options in the K20D's custom menus: #17 and #18.

The issue isn't whether the options are there. I'm aware that they are. The question is, when you're shooting raw, does that option actually DO anything - even more particularly, does it do anything to the raw data that is saved to disk? There are other options in the menus that don't do anything to the raw file - for example, sharpening, contrast (accessed on the K20D by hitting Fn, then OK). I would say that your color balance setting also does nothing, really, to the raw data. It provides a tip to your image processing program on how to display the image initially, but if you shoot raw, you can easily change that. That's one of the major reasons to shoot raw.

I've spent a fair bit of time testing this with normal (not long shutter) exposures. For raw captures and normal exposures - for example, 1/125th sec, f/2.8 and ISO 6400 or ISO 3200 - I can't see any difference whether noise reduction is set to high or set to OFF completely. NO difference. Now I want to make something very clear. I'm NOT saying that it doesn't do anything. I don't actually know. The K20D operating manual doesn't say, which is no surprise.

The slow shutter speed noise reduction option is a different option on the K20D and I have never used it. I can kinda sorta imagine that slow shutter captures present special technical problems.

Will

[Quension]

The slow shutter speed noise reduction option is a different option on the K20D and I have never used it.

That's the one that's being discussed in this thread. Slow shutter NR works by performing what's called "dark frame subtraction" on the raw data. The camera captures the image as normal, then immediately captures another image for the same duration with the shutter closed. This second image contains only thermal sensor noise, so by subtracting it from the previous image, it yields an image without (much) sensor noise. This subtraction must be performed on the raw data, and affects the raw result.

On many cameras prior to the K20D, including the OP's K10D, slow shutter NR can be turned off. This lets you take several long exposures without having to wait between them, and you can do your own dark frame subtraction later on the computer.

[LeoTaylor]

The original poster Robert has a K10D and his link is to a discussion about long exposure. He doesn't want to wait for the doubled time when NR is on. He finds for his use the NR is not needed and he turns it off.

As Quension said the K20D is different. Many on this forum have lamented that for long exposures in JPEG or RAW the CMOS sensor K20D can't turn off NR. WMBP, you don't have the choice Robert and I were discussing. The K20D sounds like a wonderful camera and has many good features but this one weakness could be a showstopper for astrophotographers. It is also a problem for shooting fireworks. Last Fourth of July I shot 4-6 second images about as fast as I could press the remote. If NR was on I'd have to wait 5-7 additional seconds between every shot.

[Robert S Donovan]

Leo is right about the differences in the K10D & K20D's noise reduction functions. I am talking about the automatic dark frame subtraction exposure my K10D takes when long exposure noise reduction is enabled. I'm not yet familiar with the K20D's options in this area. For the RAW long exposure shots I normally take, turning off the noise reduction works great on my K10D.

WMBP, you are right about the "unprocessed" RAW files. What I meant was that the files were improrted into Lightroom then reset to LR's default settings. I then took a screen capture of the RAW image being viewed on screen to eliminate any export processing. That's as close to viewing an "unprocessed" RAW file as I think you can get ;-)

[smigol]

I'm interested in how you've found working with archived dark frames for the K10D. Do you have an archive of images at various time durations, ISO settings, and temperatures?

Or do you just get a representative sample on the evening when you shoot?

[StevenVH]

I've been wondering about both NR settings in general with my K200D. At some point recently I turned both off and didn't see any obvious change to RAW images. Now I'm seeing noise in dark backgrounds when using a slow shutter speed. I'm planning to do some simple tests with NR settings to see if there's an improvement.
I'd love to hear something definitive about the subject in general, especially if it applies to the K200D as well.

cheers

[Ben_Edict]

I'm interested in how you've found working with archived dark frames for the K10D. Do you have an archive of images at various time durations, ISO settings, and temperatures?

Or do you just get a representative sample on the evening when you shoot?

Yes, please, more info! I recently tested the K20 with a series of exposures between 15s @ ISO 800 up to 160s @ ISO 3200. As you can'Ät switch off the NR (darkframe substraction) this got pretty boring and I lost half of the available time. I am now contemplating using the K10 for astrophotography, though the K20 has a much better high ISO performance in general. If there is a way to get the K10 noise Level down, I would use this body...

Ben

[Confused]

Hi there

I have to admit that I'm slightly puzzled by what appear to be certain contradictory aspects of what I've read in this thread, so please bear with me a while. I recently used my K10D whilst on vacation and occasionally took some night shots of cityscapes, using a tripod with the camera's Shake Reduction & Noise Reduction features both switched off.
Assuming I've understood this process correctly, if I had left the Noise Reduction switched ON, as Quension stated:

The camera captures the image as normal, then immediately captures another image for the same duration with the shutter closed. This second image contains only thermal sensor noise, so by subtracting it from the previous image, it yields an image without (much) sensor noise.

Yet LeoTaylor writes:

I took a third 60 second frame last night with the telescope capped and this morning subtracted the dark frame from the first light frame. This is done by astrophotographers who want to take the light frames as fast as practical and handle the dark subtraction later.

What I fail to comprehend fully in this instance is how on earth the dark frame can be subtracted later, having taken the initial photo with a K10D ? Surely the dark frame is an integral part of selecting the Noise Reduction feature ? Sorry if I am missing the blindingly obvious here, but would anyone care to clarify this matter for me ?

Best regards
Richard

[Robert S Donovan]

Richard,
(Great sceen name, BTW). See this how-to for using Photoshop for DIY dark frame subtraction.

From what I could tell (and what led me to the experiment that led to my blog post), dark frame subtraction is really only needed in cases where extremely long exposures are being taken and exteremly low noise are critical (as in astrophotography). Typically, my long exposure night shots are in the 10 second to 2 minute range and Lightroom seems to do a good job of fixing any stuck pixels.



This photo is a 10 minute long exposure shot in RAW using my DIY bulb switch and imported into Lightroom. Processing was limited to a bit of white balance adjustment. Noise in the original was a non-issue due to the ISO (100) and detail in the scene.