Color Correction Scope

miketpl wrote on 7/7/2004, 11:03 PM

In the Color Corrections Scope, can you tell me what the difference is between Gamma, Gain and Offset. It looks like they all effect the video the same way.

The terms brightness and luminance, are they not the same? It looks like they have diffrent meaning when used with video's.

Comments

Spot|DSE wrote on 7/7/2004, 11:53 PM

Think of them as Tone, Volume, and Offset. They all have similar result, but very different actions. I recommend Steve Hullfish's book on color corretion. Outstanding and simple explanations of what can be fairly complex.

BillyBoy wrote on 7/8/2004, 6:34 AM

The complex explained [edited by moderator]:

http://www.wideopenwest.com/%7Ewvg/tutorial-menu.htm

SonicJane wrote on 7/8/2004, 8:16 AM

[Added by craftech after deleted message]

For each channel there are two parameters Offset and Gain. Offset value is added to the channel while the gain is multiplied. Hue channel is special though. Since scaling the hue is not very useful both values are used as offset. The first one is simple offset while the second one is mappable.

Gain is a multiplier for the value. That means that if gain is set to 0, it preserves the values as they are. When gain is 256 all values are multiplied by 2 (twice as bright). If gain is 512 all values are multiplied by 3.

Offset adds a value to the luma or chroma values. An offset set to 16 will add 16 to the pixel values. An offset of -32 will subtract 32 from all pixel values.

Unlike brightness, gamma is a non-linear operation which does not change black (0%) and white (100%) while changing the other values. Higher gamma values produce darker mid-tones while lower gamma values produce brighter mid-tones. Affects alpha too.
Gamma adjusts gamma of the specified channel. A gamma value of 0 is the same as gamma 1.0. When gamma is set to 256 it is the same as gamma 2.0. Gamma is valid down to -256, where it is the same as gamma 0.0

John