Cinegamma Availalbe in 30p too ?

[John Morrison]

Hello,

Have been kicking this one around with my colleague, We do a lot of industrial/retail work. Training videos, corporate message videos typical production stuff. We love the look of 24 p for our acted scenarios because of the cinegamma and the motion qualities it affords, we do not care for the motion when were shooting products on the shelves especially when we shoot eng style. So we're thinking 30p might give us a compromise so we don't have 60i and 24p in a piece, we think that looks... ummm, bad. We have done some tests and with progressive versus interlace resolution setting through this we've determined we like interlaced the best for our application. Are the cinegamma settings available in any setting other than 24 p ? The image in 30p more closely resembles the 24p than the 60i ?

[David Mullen ASC]

30P might be a good compromise as long as you don't need to make a PAL version. It looks like a smoother version of 24P.

[Guest Daniel J. Ashley-Smith]

(Sorry John, just didn't want to create a new topic)

 

What is a definition for, gamma?

 

I played around with the gamma on my CRT monitor; it?s like it's brightening the image. Although when I turn the gamma right up, and turn the brightness down, the picture is still distorted. Is it the range between dark and light colours?

 

What is gamma?

 

Tnx.

Edited November 2, 2004 by Daniel J. Ashley-Smith

[David Mullen ASC]

I believe gamma is a math function describing the angle of a diagonal line, like on a chart plotting, let's say, exposure versus density (in film) or electric charge (in video).

 

Basically as you get more exposure to light, you generate more potential silver density on film (after development) or more charge (or current?) in a CCD. The gamma describes the RATE of that increase. If you have a 1:1 ratio between a unit of exposure and a unit of density, it might describe a 45-degree angled line on a chart. If you generate twice as much density for every unit of exposure, the rate of ascent of the line is steeper than 45 degrees. This describes a higher-contrast image, where you can quickly become overexposed with a little increase of exposure, and thus have an overall shorter range of possible exposures from dark to bright. A flatter rise, less than 45 degrees, would desribe a lower-contrast image because it takes a bigger increase in light level to cause a certain amount of density to form.

 

However, film only has a straight-line response to light in the midtones, and a flatter response in the darkest and brightest areas, which is why the characteristic curve is sort of "S" shaped, so film is "medium contrast" in midtones but lower contrast in bright and dark areas, which is why overexposure more gently rolls off into whiteness rather than abruptly as with video.

 

Anyway, gamma is not written in degrees, so don't get confused by my layman's description. I think it's a log function (I'm too lazy to pull out a textbook and look it up). And in video camera menus, gamma levels are just arbitrarily described in increments, let's say, from -99 to +99. But often the terms "gamma" and "contrast" are somewhat used to describe similar concepts although they are not exactly the same things.

[Alvin Pingol]

Some links on Gamma:

 

http://www.colormatters.com/comput_gamma.html

http://www.cgsd.com/papers/gamma_intro.html

[Mitch Gross]

Cinegamma is available in all modes. And 30p retains much of the desired look of 24p without appearing "juddery." I just finished shooting a project in 30p that is for American (NTSC) only broadcast.

[Phil Rhodes]

Hi,

 

Gamma is the exponential transfer function (compare lift, which is additive, and gain, which is multiplicative.)

 

Consider the "curves" editor in Photoshop. When you first open it up, it's an exactly diagonal straight line - what you put in is what you get out. If you start applying gamma to it, the line bends in the middle - what you get out is what you put in raised to the power of some number over 1, where a gamma of exactly 1 has no effect.

 

The point of gamma adjustment is that it makes the image seem subjectively brighter without clipping or crushing any detail. As a practical matter of course you will lose some information to quantisation as you squeeze the upper reaches of the dynamic range, but that's the general idea.

 

Phil

Edited November 3, 2004 by Phil Rhodes

[John Ealer]

For clients that don't like the 24p look, I've had great success in 30p. I can't tell you how many people I've turned off of Digibeta with a quick look at 30p on the SDX-900.

 

The same scene files, gamma controls, etc. etc. are all available in all modes (24p, 30p, 60i / 25 or 50Mbs) on the SDX900.

 

To my knowledge, the only thing you can't do in the progressive modes is the Digital Cumulative Gain mode.

 

J