Dynamic range refers to the range of which a camera can successfully capture the lightest and darkest areas of an image without losing detail. Once this range is exceeded, the highlights will wash out to white and the darks will turn to black blobs. So the higher the dynamic range, the better!
Often dynamic range is confused with latitude. Latitude is related to dynamic range, but is not the same thing! Latitude refers to the exposure flexibility of your captured image — so how much you can alter it in post to attain the correct exposure. Latitude is dependent upon dynamic range. While dynamic range refers to a camera, latitude refers to the image it captures.
Today, in an attempt to help out some more of you we’re going to talk about the difference between ‘dynamic range’ and ‘latitude’. Two terms that many people use interchangeably which are actually two different things.
Dynamic Range is a measurement of the size of the range of tones that a camera can record from completely black to completely white. In simple terms, the greater the dynamic range, the more detail you can see the shadows and highlights of a picture. In the old days, different film stocks had different dynamic range properties, especially from type to type. As a rule of thumb traditional black & white film has the most, then color negative film, and finally color slide film the least at about 7 stops. Now most of us use a digital sensor in the place of the film and so it’s this sensor that now has the properties of dynamic range. So if you want better dynamic range, you’ve got to buy a new camera. The good news is that today’s cameras are really pretty great in this regard, most within the 12-13 stop range which is as good as all but the best film with the best scanners.
I’d like to take a second and discuss the dynamic range of film and why it’s so hard to measure and compare with digital. You see, digital sensors are designed to be very linear, that is, if you add a stop more light the sensor will record the image a stop brighter. The down side is that when the light coming in overwhelms the sensors ability to record more light the highlights in your image “blow out”. Digital doesn’t do this very pleasantly and it’s definitely one of the few things they’ve really got to work on. Film on the other hand (and this goes for audio recorded to magnetic tape as well) is mostly linear for most of the range. However at the highlight end of the scale the film pushes back, and when you add a stop of light and then another, the film records less and less of an increase. It’s got sort of a built-in compression curve which transitions highlights to white very very smoothly. It’s very pleasing to the eye, but that same effect also makes it very hard to measure how much dynamic range the film is accurately recording. Do we count those top few stops that get compressed as ‘accurately’ recorded? I’m not sure.
Either way, let’s imagine that there’s a ruler that has black at one end and white at the other. And since I live in America and there are about 12 stops of dynamic range in a sensor, I’m going to use a one foot ruler as a visual guide. Imagine that this ruler is broken up into 12 equally sized inches each representing one stop of brightness that the sensor can measure. The 0 on one end equals black and 12 at the other end equals white with grey in the middle. Easy right? Ok, hold onto that, we’ll get back to it in a minute.
Latitude is the other term which people use interchangeably when they typically mean dynamic range. “That new camera has better latitude than last year’s model”, I’m sure you’ve heard that kind of quote before. What latitude actually refers to is how much a picture can be over or under-exposed while still getting the image you were looking for, and that very much depends on the image you’re trying to take.
So for example if you’re taking a picture which only has 8 stops between it’s darkest and lightest areas, then your camera’s 12 stops of dynamic range is overkill. That means that you’ve got 2 stops on both the shadow or highlight ends which are technically going unused. In fact if you overexposed by a couple of stops and then pulled it down by 2 stops in post, especially if you’re shooting RAW files, you should end up with an image that looks just like one which was exposed correctly. In this instance you could say that you’ve got ‘2 stops of latitude’.
To use the ruler analogy from above, if the picture you’re trying to take is only 8 inches long, you could measure it from the 2″ tick to the 10″ tick on the ruler, or from 0″ to 8″, or 1″ to 9″, etc. As long as it all fits inside the twelve inches of the ruler, then you’ll be fine.
Back in the film days, when you dropped off a roll of film at your local lab, a tech or a computer would make these kind of corrections for you when making your prints so that everything looked correctly exposed. It was the fact that film had a lot of dynamic range which allowed people to take all kinds of incorrect exposures and still delivered great looking prints. This fact was used to great effect in disposable film cameras which had a single shutter speed and aperture. They relied on the fact that you could usually get a ‘usable’ image regardless of how much light actually hit the film, especially when they could just pop a built-in flash.
Of course in the real world there are consequences to incorrectly exposing your image. Even if it fits into the dynamic range of the sensor, a stop or two (or on the odd occasion three), is about all you’re going to get back in either direction and you’ll likely have some artifacts like shadow noise. We’ve also been talking about this from the very basic point of view of monochrome luminosity. However real images have three color channels of Red, Blue, and Green each of which have a ‘ruler’ in them. So you might blow out one of the color channels and not the others, and so forth, which further complicates things like recovering highlights. It all varies from image to image.
So to wrap up, Dynamic Range refers to the size of the range of light that a camera can capture from complete black to complete white, while Latitude is the amount of under or over exposure that a particular image can handle while still fitting into the camera’s dynamic range.
How to increase dynamic range:
Your Camera
Since dynamic range is a capability of your camera, the best way to attain high dynamic range is to buy a camera with high dynamic range. For example, the high end digital video cameras made by RED and ARRI fall under this category. The new Blackmagic Cinema Camera also has high dynamic range. This video from the good folks at OneRiver Media compares the dynamic range capabilities of the Blackmagic Cinema Camera with that of the Canon 5D Mark III DSLR. It’s a perfect way to visualize exactly what dynamic range is, and the limitations of any camera in terms of attaining the correct exposure. Let’s watch:
But as we all know, one thing they do say is that money doesn’t grow on trees. So if you can’t fork over the dough for a snazzy camera, consider the following options for increasing dynamic range:
Picture Style
Using the camera you have, making conscious decisions about in-camera image settings can help to give your footage more latitude. As a general rule, turning down contrast and similar settings will help to retain more information in your image. For example, if you were to turn up contrast very high, you run the risk of losing detail in your blacks. Once that contrast is baked in to the image, it’s impossible to recover that detail in post. Alternately, if you turn contrast down, you’ll have a flat, boring image, but all of that information will be retained, and you’ll have more flexibility to tweak the contrast in post. That’s why very “flat” picture styles such as Cinestyle from Technicolor, or Cine from Marvel have been developed. If my explanation is falling flat, watch this video from Luka for more details:
HDR
If you have an iPhone, you may be familiar with HDR. It stands for high dynamic range. When taking an HDR photo on your iPhone, it works by compositing two images, taken one right after another. One image will properly expose the highlights, while the other image will properly expose the dark areas. When composited together, you get the best of both worlds in an image where both are properly exposed! Using an image editing program like Photoshop, you can do the same thing on your own, and can use more than two images. This same process is used in timelapse videos, since they are made of photographs. You may be familiar with the popular HDR Skies video? Just as the title suggests, the beautiful skies and scenic foregrounds are able to coalesce in picturesque harmony due to HDR:
In video, HDR works a little bit differently. The fact that you must roll video continuously, and that it’s not physically possible to attain identical framing from two cameras at the same time without a fancy setup are both initial barriers that must be overcome.
Magic Lantern has developed a pretty neat firmware update for some Canon DSLRs, which alternates shooting between two different ISOs between frames. You then merge the two exposures using their software.
You can also create multiple exposures of the same video file and fuse them together in post. Check out this tutorial video in which Jochem D uses Adobe AfterEffects CS4 and Photomatix Pro to do just that.
Graduated Neutral Density Filters
Last but not least, a more “old school” but just as effective trick is to use a graduated neutral density filter. To brush up on your neutral density knowledge, head on over to this Video School lesson. Unlike a regular ND filter, a graduated ND filter blocks out a varied range of light across its surface. One of these babies can come in handy when shooting a landscape scene. If you place the filter so that it blocks out more light at the top than the bottom, the effect is essentially as if you were shooting at a higher aperture at the top than the bottom, so that the brighter sky and the darker landscape are both properly exposed.
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