avisynth: how to Gain up image?

[marcorocchini]

Hi cats,

please anyone can say how to "gain" video level in avisynth? thanks

[hello_hello]

I'm not a cat.

What do you mean by "gain"?

[marcorocchini]

for example in the camera: Gain= +3dB or +6 dB

[jagabo]

ColorYUV(gain_y=X)
Tweak(cont=Y)
RGBAdjust(r=Z, g=Z, b=Z)

[johnmeyer]

The word "gain" is too vague and ambiguous. Changing the "brightness" of a video can be done in many ways, including:

• Increasing the brightness of each pixel by the same amount. This is almost never the right thing to do.
• "Expanding the histogram" so that black pixels are set to exactly 0 and white pixels to 255 (although this depends on the system used to measure brightness). This often makes the video look punchier, but is can sometimes lead to increasing the contrast too much.
• Increasing the midtones. This is often done with a gamma function. This is one of the better ways to adjust the "brightness" of a video, but how it works depends on the software you use.
• Build your own histogram transfer function. This is the best way to adjust brightness, but requires some skill.

Very often you have to use some combination of these things.

Finally, I am not a fan at all of using AVISynth for this task. Almost any NLE will do a much better job and give you all sorts of instantaneous feedback as you jiggle controls on several exposure plugins.

[usually_quiet]

Finally, I am not a fan at all of using AVISynth for this task. Almost any NLE will do a much better job and give you all sorts of instantaneous feedback as you jiggle (usually) controls on several exposure plugins.

Maybe you have not been following marcorocchini long enough to be aware that he uses Speed Razor as his NLE, and won't change to a more up-to-date NLE no matter how many problems sticking with Speed Razor causes for him. (There have been many, many problems to date.)

[hello_hello]

Ignore list: hello_hello

The irony of claiming to ignore me while referring to me in every post still makes me laugh.

[KarMa]

Finally, I am not a fan at all of using AVISynth for this task. Almost any NLE will do a much better job and give you all sorts of instantaneous feedback as you jiggle (usually) controls on several exposure plugins.

AvsPmod does a pretty good job.

[pandy]

for example in the camera: Gain= +3dB or +6 dB

Multiply contrast by 1.41 for 3dB and by 2 for 6dB.

[jagabo]

See chart:
https://en.wikipedia.org/wiki/Decibel

To double the brightness of pixels (relative to Y=0) use one of the following (eg, Y=60 will become Y=120):

ColorYUV(gain_y=256)
Tweak(cont=2.0, coring=false)
RGBAdjust(r=2.0, g=2.0, b=2.0)

Note that you may need to adjust saturation too.

[pandy]

Or use general formula lin=10^(dB/20)...
It is good to remember that 1 bit is equal to 6.206dB and half bit is equal to 3.103dB - it may be easier sometimes to operate with such approximation.