What is ETTR (Expose To The Right)?

Question

Picking up from this answer and this question, What exactly is ETTR? How it may reduce the image noise? And how is it difference from film to digital sensors?

In the answer linked above, what are the 5 stops and is it related to ETTR?

In real life how can I apply this technique when I'm shooting?

Asked by Akram Mellice

Answer

"Expose to the right" means record the brightest image you can and then reduce the brightness in post to achieve the desired level.

The word "right" comes from the histogram, where conventionally brightness increases left to right, thus increasing brightness shifts the whole histogram to the right.

ETTR helps reduce noise simply by capturing more light, which reduces photon noise, and gives a better signal to [electrical] noise ratio (by virtue of a bigger signal). The reason high ISO photos look noisy is due to low levels of light and amplifying a weak signal.

The technique works provided you don't increase the exposure to the point where it hits the maximum possible value and gets cut off, as this will result in a loss of information (known as clipping/blowing the highlights). Typically this is seen as an area of the image (usually sky) which has gone pure white.

In principle the technique works for film, certainly exposing the left and then having to push your image when printing will increase grain. However film has a different cutoff characteristic, as highlights gently roll off rather than hitting a hard limit.

Here's an experiment I did to demonstrate the effect (and rebuff a blog article which claimed ETTR didn't work):

Here's the camera metered exposure:

Here I've used ETTR and increased the camera meter's exposure by 1 stop using a longer exposure:

Finally, to show the difference here's the standard exposure with the ETTR image offset in the centre:

The reduction in noise is visible, particularly in the purple patch in the bottom right.

Answered by Matt Grum

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Are there any good open source noise removal tools?

Question

In particular that run natively on Linux.

Asked by txwikinger

Answer

There are several different plugins for gimp to remove noise.

Answered by chills42

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Why am I getting such high noise when using ISO 320/640?

Question

I'm taking photos at night with a GH1 at ISO 640 and getting a ton of noise in the dark areas.

I've seen a bunch of other peoples night time photos and they never have this much noise. I tried using a really long exposure of 25 seconds to compensate for the low light but there's still a ton of noise. Is this unavoidable or are there other settings I can use to get rid of the noise? Or am I supposed to de-noise all the images in post?

The first shot is right before the moon came out and the second shot is when the moon was fully out (its was around a 65% full moon that night). I also shot these in Aperture Priority mode if that makes any difference. Thanks for the help!!

EDIT: I was googling and I just came across Exposure to the right(ETTR). Could this be what I'm experiencing here? The images were underexposed and therefore lose a lot of values?

20mm, F11, ISO640, 25sec exposure

20mm, F6.3, ISO320, 15sec exposure

Answer

This question is probably best answered in two parts.

Part1:

You may need to increase the ISO to combat noise. This sounds counter intuitive due to common misconceptions regarding noise.

Noise is principally caused by lack of light. Lightsources emit photons randomly, the more photons you collect, the more the randomness averages out, leaving a smooth image. Fewer photons -> more random -> lots of grain.

All increasing the ISO does, is amplify the signal (and noise) you get from the sensor prior to digitization. It doesn't create noise, and as it amplifies the signal and noise by the same amount the signal to noise ratio remains the same. Needing to amplify the signal implies you have a weak (and hence noisy) signal to begin with, hence the association with high ISO and noise.

Noise is also introduced when trying to read the analogue signal. By amplifying before reading you add a small amount of read noise to a big signal, with little effect. By shooting at a lower ISO (keeping the other settings the same) you amplify less, to you add a small amount of read noise to a small signal, giving you a worse result by lowering ISO.

Part 2:

Reducing read noise by upping the ISO will help, but the primary problem you have is lack of light. You need to get more light down the lens, by either opening the aperture, or increasing the exposure time.

If increasing the exposure time/aperture causes other parts of the scene to be too bright (to the point where they show up pure white) then you have an additional problem that the dynamic range (the difference between the brightest and darkest parts) of the scene is too high, this can be fixed by using graduated filters, or by combining multiple exposures.

If you have a static(ish) scene I would recommend shooting several identical 25s exposures and then averaging them in software to reduce the noise. This is analogous to having one very long exposure, except without problems due to overexposure of certain areas. This is how most good DSLR astrophotography is done.

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Can I get noise reduction in Aperture that even gets close to the quality of Lightroom's?

Question

I've been looking for a new Library / Photo Editing software, iPhoto isn't really cutting it any more. I've been using both Aperture and Lightroom a bit now (trial licenses) and I noticed a big difference in the noise reduction capabilities.

Lightroom does a really amazing job with noise reduction on some of my long exposure northern light photos. Apertures noise reduction on the other hand barely makes a difference. This might be due to how I use Aperture and Lightroom, but I've seen reviews that praise Lightrooms noise reduction while almost bashing Apertures (lack of).

I like how Aperture creates "Libraries" and organize the photos. The "do what you want at any time" aspect of Aperture is also something I prefer, but it's extremely slow on my computer which is quite fast (MacBook Pro 15" Early 2011, i7 4GB Ram).

I guess my question would be: Is there any other really good noise reduction plug-ins for Aperture? Can I get noise reduction that even get close to the quality of Lightrooms in Aperture?

Answer

Yes Lightroom 3.6 noise reduction is quite good but not great. You can get better results with dedicated software. I've read a number of reviews of various software packages and plugins but there is only one I personally use: NIK Dfine 2.2

I found it to be FAR better then Lightroom and NIK is also available for Aperture. How it works in Lightroom is that you have to select your image then right-click and choose edit in NIK Dfine. This opens your image in the plugin application where you work on the noise reduction. Once your work is completed, your image is added into the Lightroom library. You can choose to edit the original or a copy of the image with adjustments. The plugin is not seamlessly integrated within the application framework as the word "plug-in" would suggest, but it is not very cumbersome to use. Personally, I use Lightroom tools for most of my work and only use specialized plugins such as this one for selected photos.

After your noise reduction is complete I would also suggest to use more advanced sharpening utility. Again, I use a NIK plugin Sharpener Pro 3.0 for the occasional photo i deem worthy.

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Where does the noise come from in a long exposure?

Question

I created another test. This time I exposed for 36 minutes, because I wanted to test star photography. This is not meant to be a nice photo; I really just tested.

Camera was inside the house behind the window (it is too cold to go out) in dark. Minimal light from other room came from behind the camera. It is a Canon EOS D1000 set on BULB, F29, ISO800

The question is: Where do the blue and red dots (noise) come from?

Answer

Well, perhaps you should have gone out after all :)

The noise is thermal noise, which will become noticeable as your sensor heats up during a long exposure. In astrophotography, it's quite a common problem.

Some ways to reduce such noise:

• cool sensor down, e.g. by shooting in the cold weather. Note that cold also negatively affects battery life.
• set the camera to take a dark frame with same settings (to get just the noise) and subtract it from the image; this can be either done manually (taking a second frame with lens cap on) or automatically by camera (the feature is called Long Exposure Noise Reduction or something similar).
• using a stronger noise reduction setting in camera; this may also make the photo softer overall.

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Is there any noise difference between averaged and long exposure photos?

Question

Let's suppose I'm on a tripod, photographing a perfectly still scene (also dark) and I take these photos:

• 5 photos at ISO 3200 and 1s exposure
• 1 photo at ISO 100 and 5s exposure

There is a common thing between the items, and it's the total time used.

The EV of the first item is much higher, right? Now suppose I average the 5 photos at ISO 3200 to reduce noise, producing a single image.

After that, I take the ISO 100 photo and I adjust levels (which would increase noise) to reach the same EV of the blended photo, in a way if I look these 2 photos from far away they'd look the same.

Would the noise level be equal, comparing the blended photo and the levels adjusted photo?

I hope you understand my point.

EDIT

In response to drewbenn's commentary

Also, I don't think that blending the 5 photos will reduce noise the way you think it will

Blending photos reduce noise a lot, in fact here is an example:

I took 20 photos of a tree with: ISO 1600, F4.1 and 2s exp. The upper image is showing how much noise any of those images have. The lower is showing the result of averaging the 20 photos in one.

Sory for the bad focus.

As you can see, the noise gets almost completely deleted

EDIT2

For the ones who are asking, I used a very simply command of imagemagick to average the images:

convert [input1.JPG input2.JPG ...] -average output.JPG

If I have some time later, I'll try to conduct one of those experiments you're talking about. I guess there is no a static pattern and it'll vary on each camera.

EDIT3

I've also done a experiment a little more different:

This is the Scene:

And I've taken these set of photos (the aperture is always the same), I used manual mode.

• 01 @ ISO 100, 0.6s
• 02 @ ISO 200, 0.3s (averaged later)
• 04 @ ISO 400, 1/6s (averaged later)
• 08 @ ISO 800, 1/13s (averaged later)
• 16 @ ISO 1600, 1/25s (averaged later)

Each set has the exactly same EV, these are the results, in the same order:

It seems that a higher ISO, there is less noise but less details as well.

Answer

Provided your ISO100 image was not underexposed I wouldn't expect a noticeable reduction in noise (except maybe in the deep shadows) with the 5 1 second ISO1600 images blended together.

In the infamous other thread I demonstrated that a 1/30s ISO100 will contain more noise (lower signal to noise ratio) than a 1/30s ISO1600 image. Same amount if light but the higher ISO had less noise.

The reason for this was that the read noise is proportionally greater in the ISO100 image (as readout happens after amplification). In a "correctly" exposed ISO100 the read noise is so small compared to the signal that any reduction in read noise is probably not noticeable.

edit: just did the experiment

I shot one photo at ISO100 16 seconds, and 16 shots at ISO1600 but only 1 second. All images were well exposed. What follows are two crops, the top row is a single ISO1600 image, and the bottom two are the 16 ISO1600 images averaged in Photoshop, and the ISO100 image. I wont tell you which way round the bottom two are, to see if anyone can actually tell the difference - I certainly can't!

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Does the order of sharpening and noise reduction matter?

Question

I have been shooting for more than three years, but I never do too much in post-processing. I tend to be strict and keep in mind that PP can only do little to save an otherwise-great photo.

I was going to enter the "Photo of the week" thing, and I was doing sharpening and noise reduction in Photoshop.

NR makes your photo blurry, while sharpening amplifies noise.

I wonder, does the order of these operations matter at all?

Should I apply noise reduction and then unsharp mask, or the other way round?

Answer

Simple answer is YES!

Noise is an undesirable artifact, and many operations can enhance its appearance, not just sharpening. Tweaking curves, adjusting contrast, working exposure, etc. can all have some impact on the noise that is present in an image...although sharpening tends to have the greatest impact. It is important to handle the bulk of your noise reduction as one of the first steps of your development workflow. You should not necessarily aim to "eliminate" all noise...rather your goal should be to reduce the effect noise has on an image as much as possible without adversely affecting detail that you wish to keep. The tool you use to remove noise can have a HUGE impact on the results as well...Photoshop in particular is not really known these days as having the best noise reduction tools. Lightroom has some fairly excellent noise reduction, and there are other tools like Noise Ninja and Neat Image that also do an excellent job.

Keep in mind your final presentation format and size...a LOT of noise that may be present in an image at 100% is going to get "absorbed" (for lack of a better term) into the final presentation format. Prints can sometimes exhibit pronounced noise, particularly when the noise contrasts well with the base image. Usually a moderate amount of noise, particularly in smooth gradients, can be beneficial to final print output as it normalizes content and eliminates harsh transitions. Presentation on a computer screen is often best done at significantly lower resolution than the original image, and downscaling is a superb mechanism for eliminating noise. If you start out with a moderate amount of noise, or an even distribution of high amounts of noise, downscaling for display on a computer screen (i.e. via a web page) can be all the noise reduction you need.

Sharpening is a facet that is closely linked to the viewing medium of an image. Generally speaking, its best to save sharpening for last. Not only that, its best to keep sharpened images saved as separate files from your primary work image (which in turn should be separate from your original master image.) The amount of sharpening done, and the type of algorithm used and its settings, should be matched to the output medium for your photos. If you intend an image to be viewed onscreen, the kind of sharpening you do will be different than if you intend to print. The size of the final image for either medium will also affect how much sharpening you do, and how that sharpening is done. It's a good best practice to save resizing, cropping and sharpening for the very last two steps of your image editing. Duplicate, crop, resize, sharpen. If sharpening greatly enhances the remaining noise in your image, you may also want to do a final "light" pass of noise reduction to minimize it as much as you can without adversely affecting sharpness.

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What are the pros/cons of the high-ISO noise reduction feature on D90?

Question

So my D90 offers "High-ISO Noise Reduction". Sounds like a good thing, but obviously there must be a cost of some kind. The settings are "Off", "Low", "Normal", and "High", and the default is "Normal".

What are the pros and cons of using this feature? Why not always set it to "High"? Or, should I be turning it off?

Answer

The pro's are self-evident:

• Lower noise on high-iso

The biggest con:

• Loss of detail

The high-iso noise reduction might remove detail mistakenly. While newer camera algorithms have gotten better at it, it's still not fool proof.

The settings between Off, Low, Normal and High dictate the amount of tolerance used for the setting, which affects the amount of detail that might be lost.

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How can I keep my camera cool on a budget?

Question

Is there a way to cool the camera without buying a new hardware? How do you determine that the camera is NOT cool ATM? What temperature can be considered hot for the camera sensor? Does cooling really reduce the noise in the pictures?

Answer

In general, the camera's manual will tell you the operating temperatures for the camera.

Like all pieces of electronics, excessive heat isn't good for it. That said, I've only seen anecdotal evidence of heat adversely affecting image quality. It seems more common for batteries to stop working.

As for noise, you're probably going to have this issue in broad daylight, maybe in a desert. Your problem will be to get less light to the sensor, not worry about low light levels where noise is usually a problem.

I'd get a decent camera bag, in a lighter colour, and keep my gear in the shade whenever possible. Avoid using icepacks or similar or you will probably get problems with condensation.

Cooling is used in astrophotography, but those sensors are mostly CCD's, and the exposure times and low light levels are an order of magnitude longer and lower, respectively. I don't know whether CMOS sensors have the exact same issues as CCD's with heat when used for long exposures.

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Why is dark-frame subtraction on my Pentax camera shorter than the exposure time?

Question

When my Pentax K-r applies long exposure noise reduction (dark-frame subtraction), the processing time required for this operation is less than the exposure time. For example, my camera may perform noise reduction for 10 seconds after a 15 second exposure. Why?

Answer

The manual gives you your answer:

Determines conditions such as shutter speed, sensitivity, and internal temperature, and automatically applies Noise Reduction as necessary. (default setting)

This implies that the algorithm for noise reduction isn't a simple 1:1 match with the exposure time and, coupled with the quality of the K-r/K-5 sensor family, the amount it would normally have to apply would have been less than with the prior cameras.

For myself, I have it turned off for my K-5s. I would rather deal with the noise after the fact and not have the camera lose time repeatedly doing this action.

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Should I use in-camera noise reduction, or is it better to leave that for desktop-based post-production?

Question

Should this be done using image processing software like Photoshop or the built in function of the camera ?

It seems a program like Photoshop would use a much better algorithm than what would be available in the camera, or does the camera do something else before taking the image?

Isn't the logic here the same as the logic for digital zoom (usefull only when shooting in a compressed format, as the zoom is done before compressing)? Or is there something else?

---

Related questions:

• Should I use "exposure compensation" setting while shooting?

• What camera settings may affect a RAW photo?

Answer

It should be done in post-processing. You have absolute control of the noise-reduction parameters at that point and can rethink a setting if it smears your image too much. It's best to shoot in RAW and postpone what decisions you can until you get into Lightroom or Photoshop or [insert tool of choice here].

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Is in-camera high-ISO noise reduction worthwhile?

Question

I shoot in RAW and post-process in Aperture where needed.

Does the in-camera noise-reduction do anything that I can't do in Aperture or other post-processing software? It seems to add a bit of time to the camera's saving process, and I wonder if I can just defer it to my computer, if/when I decide I need some noise reduction.

(I know that the long-exposure NR feature shoots another dark frame, which is something that can't be done after the fact. But they are individual settings on my Pentax.)

Answer

If you shoot in RAW, the in-camera noise reduction probably does not take effect, and if it did, it is really reducing the value of RAW on your camera. When you shoot RAW, you really just want the original output from the sensor with as few modifications applied as possible...none at best. You have far more control over noise during post processing, and far better algorithms at your fingertips to combat that noise with the more powerful software you can run on your computer.

I would recommend you keep your RAW images as bare-bones and neutral as possible, giving you maximum capability in post processing. Noise reduction, highlight tone curves, and other such features should generally be disabled when shooting RAW. Additionally, its normally (but not always, sometimes you may wish to choose alternatives) best to use AWB and the standard or neutral tone curve/picture setting of your camera to produce as "original" an output image as you can.

Dark frames are a slightly different matter than your average noise reduction. They can be useful when you are doing very long exposures, such as during astrophotography. You should enable Long-Exposure NR/Dark Frames on an as-needed basis when the shoot actually calls for it.

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