I understand how audio gain works, but the video equivalent would be letting more light in (ie giving a slower shutter speed/opening iris more). But how does the DVX100a have these gain settings that effect picture without changing the iris/shutter speed etc? Is it some kind of digital enhancement?
How does GAIN work? (not talking audio here)
- Thread starter jezbond
- Start date
Re: How does GAIN work? (not talking audio here)
The initial signal level coming out of a CCD chip is very low and togheter with that signal there is also a fixed amount of noise. ( determining the basic S/N ratio of the cam). Before getting digitized there is a certain amount of gain (analog) applied which is then referenced in your cam as "0 db gain". If you set for higher gain, the analog signal level will go up without altering anything in the optics. Of course the noise will go up too. If for instance, you don't get enough light, the video signal level will become too low. You can correct for 100% level again by adding extra gain, but also the fixed noise is (extra) being amplified. From the above one can understand that, as long as the initial S/N is not specified, all camera's can get high sensitivity figures..it's just as matter of setting the initial gain (0db gain) high enough. So every cam can get basically a F11 or F13@2000lux figure. If a cam is being designed for (commercial) high sentivity figures it happens that it is already noisy at 0db gain. Setting for higher gain is allmost unacceptable because of the noise problem. Pro cams with an initial S/N of 60 db can easely get 15 db gain-up without becoming too noisy.
The initial signal level coming out of a CCD chip is very low and togheter with that signal there is also a fixed amount of noise. ( determining the basic S/N ratio of the cam). Before getting digitized there is a certain amount of gain (analog) applied which is then referenced in your cam as "0 db gain". If you set for higher gain, the analog signal level will go up without altering anything in the optics. Of course the noise will go up too. If for instance, you don't get enough light, the video signal level will become too low. You can correct for 100% level again by adding extra gain, but also the fixed noise is (extra) being amplified. From the above one can understand that, as long as the initial S/N is not specified, all camera's can get high sensitivity figures..it's just as matter of setting the initial gain (0db gain) high enough. So every cam can get basically a F11 or F13@2000lux figure. If a cam is being designed for (commercial) high sentivity figures it happens that it is already noisy at 0db gain. Setting for higher gain is allmost unacceptable because of the noise problem. Pro cams with an initial S/N of 60 db can easely get 15 db gain-up without becoming too noisy.
darmanb
Well-known member
Re: How does GAIN work? (not talking audio here)
+ 3 dB = opening up 0.5 stop
+6 dB = opening up 1 stop
+9 dB = opening up 1.5 stops
+12 dB = opening up 2 stops
+18 dB = opening up 3 stops
+24 dB = opening up 4 stops
Extra gain = decrease in signat-to-noise ratio = increase in noise in the picture.
+ 3 dB = opening up 0.5 stop
+6 dB = opening up 1 stop
+9 dB = opening up 1.5 stops
+12 dB = opening up 2 stops
+18 dB = opening up 3 stops
+24 dB = opening up 4 stops
Extra gain = decrease in signat-to-noise ratio = increase in noise in the picture.