Stops (Dynamic Range)
From Wikipedia, the free encyclopedia
- For other uses, see Dynamic range (disambiguation).
Stops (in terms of Dynamic Range) are the amount of different shades between pure black and pure white.
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[edit] Measurement
It is hard to measure stops by just a number or equation. The way amount of stops get determined is by a well trained Cinematographer or DP's eye. A stop is actually an exponent to the base number of 2. So 5.5 stops (average DV Video) is 2^5.5 or a 45:1 contrast ratio. When we say how many stops a device has and we are talking about blacker blacks, whiter whites, and saturated, beautiful colours the image has a high number stops or has much contrast ratio. When we talk about the blacks being more like dark grays and the white have yellowish or blueish hue to them (depending if you are shooting outside or not) and not any really pure colours. The colours are more blended into one another. Each stop is equal to 5.5 dB which is 550,000,000 times brighter than the lowest light level. So 11 stops is 66dB and is 10,000,000,000 times brighter than the lowest light level.
[edit] Review of Contrast Ratio
Contrast ratio is pretty much the same as stops. Most TV's today such as various rear-projection and LCDs, have a 2000:1 contrast ratio about same as film. Contrast ratio is the on/off difference. 1 is off and the high number is on. 66dB is film and has a 2048 contrast ratio. Digital video is only 1.45dB which is way lower than film.
[edit] Advantages to having a High Dynamic Range (high amount of stops)
The Advantages to having a high number of stops is mostly for the purpose of post production. In the DI workflow (Digital Intermediates) film is scanned onto the computer and converted into digital files. Then after Editing, Audio Editing and Visual Effects have done their work it goes to a colour grading system where they colour correct the film and get the whole film to match up even if the lighting isn't quite right or the Visual Effects don't match up the grading team can fix that because of the High Dynamic Range. This means that in Film you don't have to just nail it. You can overexpose or underexpose and fix it in post.
[edit] High Dynamic Range Imaging
Main Article: HDRI
High Dynamic Range Imaging is where a series of the same image is shot with a digital camera with multiple exposures. The Visual Effects Studio Double Negative has used HDR images in a lot of their Visual Effects films including World Trade Center and Batman Begins. They took Canon SLR cameras and shot virtual sets at a variety of exposures piecing them all together with their proprietary tool "STIG". This creates many plates at a variety of exposures so the backround can be matched with the lighting of the live action shots. Double Negative has now got the OpenEXR pipeline nailed down after the two movies using some of the proprietary tools on their new picture Flyboys.
[edit] Film
Film has about 11 stops. And a contrast ratio of 2048:1 or about 2000:1. Film is currently the highest amount of Dynamic Range in motion picture. It is over ten times the amount of even the highest quality and clarity of video.
[edit] Video
Video has about 5.5 stops. Or a contrast ratio of about 45:1. Video is pretty limited because it only has 145 million variations of different brightness level.
[edit] See also
- RED Digital Cinema
- Genesis
- Film
- Digital Video
- Video
- 4K
- Exposure
- HDRI
- Contrast ratio
- DP/Cinematographer
- Dynamic Range
- OpenEXR
[edit] External links
- [1] Dynamic Range of Sensors
