selmslie Loc: Fernandina Beach, FL, USA

There are two aspects of dynamic range:

1. The capacity of the sensor itself (100%)
2. The numeric capacity of the raw file (for 14 bits, a value up to 16,383)

When there are more photons reaching the sensor than it can record for a particular pixel, it fills up and can go no higher than 100%. For most cameras at base ISO, when a pixel reaches 100%, all of the corresponding bits in the raw file will have a value of 1 (numeric value 16,383) and no higher value can be recorded.

At less than 100% of the sensor’s capacity any of the bits for that pixel might be 0 or 1 and the corresponding numeric values will be between 0 and 16,383. For a totally dark pixel, the sensor will record 0% and all of the corresponding bits in the raw file will be 0 and the corresponding numeric value will be 0.

At base ISO, if the capacity of the sensor has not been exceeded, the capacity of the raw file will not be exceeded either. The full dynamic ranges of both the sensor and of the raw file are being used.

What happens if you then drop the exposure in half and double the ISO (gain)? The sensor will only see values from 0 to 50% but the raw file will still record numeric values of 0 through 16,383. The recorded image will look just as bright so you may not see any change in the image – yet. The full numerical dynamic range will have been used but only half of the sensor’s physical dynamic range.

Repeat this and the sensor will only see values from 0 to 25% but the raw file will still record numeric values of 0 through 16,383. You can keep going. What is happening is that, although you are using the full numeric dynamic range of the raw file, each time you cut the exposure in half you are also discarding half of the remaining dynamic range of the sensor.

By the time you reach ISO 6400 you will only be using 1/64th (1.56%) of the sensor’s physical dynamic range but the recorded image will look just as bright because the raw file still contains values from 0 to 16,383. What has been happening to the noise? Each time you doubled the ISO (gain) you also doubled the numeric value of noise in the raw file. Your signal to noise ratio has been cut in half at each step, except for a little more effort the camera might apply to noise reduction at higher ISO values. You probably started to see some noise at around ISO 800 or 1600 and it continued to become more apparent the higher you pushed it.

As soon as you go above the cameras's base ISO it becomes possible to exceed the raw file's numeric dynamic range without actually exceeding the sensor's physical dynamic range. The pixel will be recorded as blown out with a value of 16,383 but the sensor's photon limit may not have been reached.

When someone says they are using the camera’s full dynamic range by using ETRTR/EBTR, if they are not also using base ISO, they are referring only to the raw file’s numeric representation of the image. They are not accessing the full dynamic range of the sensor.

rjaywallace Loc: Wisconsin

This is interesting, but I'm not clear what your bottom line recommendation is. Should we NOT try for maximum use of a camera's dynamic range? What are you suggesting OUGHT to be done in order to utilize the available dynamic range in order to achieve the best image quality of our photos? Should we aim for something less than 100% of DR, say 70% or 80%. I'm not disagreeing with your thinking, but wondering how best to apply it in order to create "better" photos.

selmslie Loc: Fernandina Beach, FL, USA

Which dynamic range (DR)? The sensor's physical DR or the raw file's numeric DR? It depends on the DR of the scene - more specifically of the part of the scene you care about.

If you are capturing a scene with a narrow DR and you are using a low ISO, you don't really need to sweat this issue. Your exposure can be off +/- a stop or two and you can adjust it later in post processing. Your optimal exposure is the one that will be easiest to develop from raw in post.

You do not need to try for the maximum use of the camera's dynamic range. Instead, aim to use an optimal DR of the sensor that is enough to cover the DR of the scene. Then chose the ISO to get an optimal exposure - "optimal" being whatever it takes to make it easier to post-process. This might mean pushing the histogram to the right or left but, more often than not, that will not be necessary.

If the scene has a wide DR then you need to consider whether you can use a low ISO to have a wide DR at the sensor. Keep in mind that, as you raise the ISO, the sensor's DR will get narrower.

As for the raw file's numeric DR, that is mainly a numbers game. You can raise the camera's ISO by one stop or move the Exposure (gain) slider in post by one Ev and achieve the same result.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Your discussions are interesting, but . . .

ETTR will help you maximize the dynamic range at a particular ISO setting, especially important when the ISO is so high that you are dealing with a narrow DR. But less so if you are working with a very high contrast scene. Send me a PM if this doesn't make sense to you. . . I've had a little too much eggnog, and I am afraid of fat fingering something that won't make sense. Merry Christmas (and all the other holidays that you may/may not be celebrating)!

selmslie Loc: Fernandina Beach, FL, USA

You are correct. As I have said elsewhere, you need to compare the DR of the camera at whatever ISO you have used to the DR of the scene and fit the scene into the space that is left. That may mean getting close to or slightly beyond the right end of the JPEG's histogram - ETTR/EBTR.

There is always the risk that you don't really know how far you can get away with pushing it or that you can't easily judge the DR of the scene. Bracketing might give you some cushion. HDR might be your only resort.

See also: http://www.uglyhedgehog.com/t-430868-3.html#7247715

Happy Holidays!

TriX Loc: Raleigh, NC

Thanks for The detailed explanation and serious thought on this oft debated subject. As you note, the usable dynamic range can be bounded by the sensor or A/D on the the high end and noise on the bottom, and we can choose to use that range however we think best. If we have a camera with wide dynamic range and a low or medium scene DR, then you have lots of DR to play with and can underexpose to give ourselves lots of room on the high end (to prevent blowing out highlights). On the other hand, if your particular camera has a lower DR at base ISO, and/or you need high ISO because of shutter speed & DOF requirements and low light, then you need to be more careful as to how you use the DR you have available - depends on the camera, the scene and the exposure requirements.

Very similar to audio recording. When DR was limited to 60 dB or so because of tape and LP noise, the recording engineer pushed the gain right up to the limit- very close to overload and distortion (and occasionally beyond). But with the advent of DAT tape, dbx encoding and digital audio, suddenly they had 90 dB to work with and could allow a bit more headroom to prevent overloading on peaks without audiable noise.

Rather than follow specific rules, we need to understand the limitations of our equipment and processing and learn to judge light and the DR of the scene we're photographing. Personally, I find the old zone system (and an occasional spot reading) still most useful for evaluating a scene.

Happy Holidays everyone. My guests are arriving, and I'm fixing myself a drink 😈

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

After a little more eggnog I am thinking more clearly now.

And that is where experience with your camera and high ISOs and a solid foundation in zone system exposure analysis comes in handy.

Where did I put my glass of eggnog?

CO

I've read about the gamma correction that cameras do to attempt to distribute tonal levels more evenly. This is performed when the camera generates an image in either the .jpg or TIFF format. It seems this process can help to reveal more detail in the darker regions of the image and prevent darker areas in the photo from "blocking up". I'm wondering if all RAW converters do this.

selmslie Loc: Fernandina Beach, FL, USA

Yes, the short answer is that your computer will do a better job than your camera.

jack30000

I'm still new here - new enough to know when I'm confused. Never heard of ETTR or ETBR before, so with a little help from Google, I know what the acronyms mean. At least superficially. There was another thread here today about underexposing because you can recover detail in the shadows but not in blown out highlights.

So are we saying that in low contrast (i.e low DR?) scenes, over expose (ETTR) but in high contrast scenes, underexpose?

selmslie Loc: Fernandina Beach, FL, USA

No, there may be no reason to over- or under-expose in either case, especially if you are only using JPEG and not planning to develop from the raw file.

In a low contrast scene you are not likely to have a problem with blown highlights or with noise in the shadows unless you are using a high ISO.

In high contrast scenes you need to be careful not to blow the highlights. This might require under-exposure but, if not, there is no compelling reason to over-expose. More on that later.

When you use a high ISO, your camera's DR is reduced and it will be more difficult to protect the highlights. You have to be careful in that case.

Dalek Loc: Detroit, Miami, Goffstown

I don't worry about DR or lens breathing. I like my Nikon D500 and D5 and the lenses I have as they are good enough for me.
Merry Christmas and enjoy your eggnog.

Grnway Loc: Manchester, NH

Merry Christmas, Scotty (and fellow 'Hoggers)

The technical analysis that I, admittedly, just glossed over has caused me to skip the eggnog and go straight for the bourbon.

I believe that most higher end cameras have a 7 stop dynamic range capability of processing in one shot, whereas the human eye has 9-10 stops capability. Could be wrong, but I vaguely remember those numbers from my photography course.

catchlight.. Loc: Wisconsin USA- Halden Norway

I'm with selmslie again...reality 101 ;)

TriX Loc: Raleigh, NC

The best DSLRs have a dynamic range of 11.5 -12 stops, while the human eye, if you consider both dark adapted (scotopic), light adapted (photopic) and the median area (mesopic), has a range of approximately 20 stops. Since photos are usually viewed while light adapted (photopic vision), 10 stops is probably a good estimate.