how to convert (TV NTSC gamma -> PC monitor gamma) ,avisy

[kuramaua]

how to convert (TV NTSC gamma -> PC monitor gamma) , with avisynth? (PC monitor gamma -> TV NTSC gamma, too)

[manono]

Hi-

ColorYUV(Levels="TV->PC")

or vice versa.

http://www.avisynth.org/ColorYUV

[kuramaua]

desculpe manono, acho que fiz a pergunta errada.

o video NTSC original tem o gama de 2.2
o monitor aceita o gama 2.5
quais parametros devo usar no colorYUV para converter o gama de 2.2 para 2.5

The gamma value for NTSC/525 is set at 2.2
Monitors, then, are said to have a gamma of 2.5
which parameters should use in the colorYUV to convert the gamma of 2.2 for 2.5 ?

[jagabo]

ColorYUV(Levels="TV->PC") converts the intensity range from 16-235 for NTSC TV to 0-155 for the PC. That is a linear transformation, not a gamma correction.

I'm not sure how to calculate the gamma correction for going from 2.5 to 2.2. If you just take the ratio (2.5/2.2) you get 1.136 implying a setting of 35 in the ColorYUV() filter. Try:

ColorYUV(0, 0, 35)

That made the image on the PC monitor look very close to what the video normally looks like on TV.

[manono]

Maybe you'll like the Levels filter better. It has a Gamma setting and you can set it for PC or TV also:

http://www.avisynth.org/Levels

[edDV]

Is it wise to change gamma in the file?

It depends on what your goal is. Normally gamma is optimized at the display adapter level to match the local display. If the file is only destined to a LCD computer monitor, then may be it is wise to change the file (e.g. imbedded in an application).

Gamma correction could also be applied as part of the capture process provided you had a calibrated reference monitor from which to make judgement.