right exposure for shooting with cine gammas
Posted 03 September 2007 - 07:40 PM
Posted 04 September 2007 - 04:36 AM
Gamma settings are just a tool for redistributing luminance across the tonal scale. If you're going to do that (manipulate the tonal scale), you need some point of reference to compare them, AND by which to judge exposure. Usually that reference is midtone, as it is with film. I've seen too much confusion and botched exposures when people try to use white as a reference -- thinking that whites are somehow sacred in video -- and let their midtones wander all over the place as a result...
Pick a gamma setting that gives you the picture quality (i.e. tonal reproduction) you like. Test this gamma setting with a properly lit Caucasian face (and a proper monitor) and see where the various zebra levels fall. Pick a zebra reference that's easy for you to find while shooting. Practice and commit this to memory before shooting your doccu footage.
Without a solid reference for what the gamma controls are doing (testing), the exposure looks like (a proper monitor), or what luminances the camera is recording (waveform monitor), you have no reference for exposure. At some point you have to review your footage and then decide what combination of gamma and exposure gives you the look you want.
Posted 04 September 2007 - 06:22 AM
Posted 04 September 2007 - 10:42 AM
Posted 13 September 2007 - 05:57 PM
Normal tv-gamma in a videocamera is around 55 IRE and not 50 IRE, because it´s a gamma for tv and not theatre. A TV gamma has to been watched in a lit envoirenment, so the midtones must be brighter.
It's true that the reference for medium gray in standard def TV has always been 55 IRE, not 50. I said "close to 50" because that number is not carved in stone, especially since the same image these days may be displayed in different ways (LCD screens, video projection, or filmout). Many people use 50 or even 45 IRE as a reference even when the image is destined only for TV display. Keep in mind that CRT displays already have a higher gamma than LCD screens or film projection, so you don't have to push your midtone reference too bright just because it will be viewed in a brightly-lit room. But my point was that the midtone reference should always be the same between gamma settings, whatever number you chose.
I don't know how Canon has programmed their gamma settings, but if they are like Panasonic then the gamma presets affect the entire gamma curve, not just the midtones. You might find the same midtone exposure between two different gamma presets (and the same absolute black and white), yet the shadow or highlight curve might be a little different.
Also keep in mind that with higher gamma (brighter midtones) color will appear less saturated and vice versa. Gamma curves that are overall flatter usually need an andjustment to the color saturation to appear "normal." Panasonic's "Cinelike" color matrix is designed to take care of this; I'm not sure how Canon deals with it.