Helpful Posts: 0
2nd July 2008, 08:49 AM
Just wondering if someone could help me understand Dynamic Range? I just can't quite get my head around it.
2nd July 2008, 03:40 PM
Re: Dynamic Range
Let's see if I can... in short words, Dynamic Range is the "distance" between shadows and highlights that a sensor can catch from a scene.
The amounts of lights, in photography, are usually expressed in EV values, a simplification made to not use specific light nomenclatures, like lumens or candels. A value of EV -3 is approximately the light coming from stars, and EV 20 is approximately the light coming from a nuclear explosion, or directly the sun.Each EV value is considered a full step, commonly called "stops".
The dynamic range would be "the amount of steps that a sensor can record between whites and blacks".
Let's suppose an scene where we have a big difference between shadows and highlights. Even if in the scene we have the shadows around EV4 and highlights around EV14, how much of that range can the sensor record? Well, that amount would be the Dynamic Range. Let's suppose we have a P&S digicam that has a Dynamic Range of 7 stops. We measure an appropiate exposure for the shadows. So, everything that is between EV4 and EV10 will be recorded with enough differentiation to perceive detail. But, above that, will be blown. And viceversa, if we expose for the highlights -that were in EV14- we will record detail in the shadows down to EV 8, but below that, detail will not be recorded.
In P&S digicams, this is usually around 6-7 stops before the sensor can not record more detail in highlights or shadows, at least not enough for us to differentiate details. In DSLRs, this is usually between 8-10 stops, and film is in the neighbourhood of 11 stops. Of course these are rough generalizations, as if we would have to take each sensor and film particularities for each different scene the size of the list would be too long.
I hope this explains a little! And please forgive me my english mistakes, it's not my mother tongue.
3rd July 2008, 12:25 AM
Re: Dynamic Range
In general (that is, not specifically relating to photography,) dynamic range is the ratio between the largest and smallest. The next question is... largest and smallest what? The answer is...anything.
For example, a typical bathroom scale will measure from 5 to 300 lbs, giving a dynamic range of 300:5, or 60. A laboratory scale may be able to measure between 2 and 1000 lbs., giving it a larger dynamic range of 1000:2, or 500. Having a larger dynamic range is generally equated to being more sensitive.
In photography, the ratio between the largest and smallest amounts of light that a camera can capture is the cameraís dynamic range. In the example above we used pounds. In photography light is typically referenced in EVs, or stops. Itís an odd measure because itís relative, whereas pounds are absolute (one pound always weighs one pound.) However, with light one EV (or stop) is equal to half, or double, the previous amount of light.
So if you take a given amount of light and then double, double, double, and double again, you can say there are four stops between the starting amount and ending amount. Compact cameras have 5-6EV of dynamic range. Professional cameras can have a dynamic range of 8-9EV, or more. Professional cameras are more sensitive to light than compact cameras.
Thatís dynamic range. But what does it mean to have a large dynamic range? A camera with a large dynamic range can take a picture that shows bright and dark objects at the same time. When a camera with a small dynamic range takes the same picture, the bright objects are too bright and have little detail, while the dark objects are too dark and also have little detail.
See this page for more info.
5th July 2008, 06:04 AM