Black Gamma and Noise.

[Paul Kellett]

Page 75 of the manual.
Black Gamma

-99 to +99

Adjust the level of black gamma function that emphasizes only the dark areas of the picture to clear the tones or on the contrary de-emphasizes it to reduce noise.


So does this do the same as crispening to reduce noise ?
I'm trying to reduce noise in the blacks for when i shoot in low light.

Paul.

[Alister Chapman]

Black gamma adjusts the bottom of the gamma curve up and down, in effect stretching or compressing the darker parts of the image. By using a + setting you can make dark areas of the image brighter which lifts those areas up out of the noise that can effect the darker parts of the picture. However if you bring the black gamma up too high you loose contrast and can end up with your darks raised so high that it is very difficult to get any detail in the darks and the image doesn't look good.

[Paul Kellett]

So adding black gamma reduces noise by "brightening" the blacks ?
I thought that would add noise, like having the effect of adding more gain to the blacks.

Ideally, for when i'm shooting in low light, maybe wedding receptions/disco's i'd like to add gain but not so much in the blacks, can't see much detail in dark jackets anyway or outside in dark skies.

I've played with the crispening but it doesn't seem to do much.

I'm happy with the pp i use but just want to lower the noise a bit when using the gain, i do go up as high as +12db sometimes.

Thanks for the explanation Alistair.

Paul.

[Bill Ravens]

Once things sink too deeply into the blacks, overall s/n gets overwhelmed by "n" (noise) The dark current of the sensor produces noise where no image exists. The idea, here, is to raise the shadows above the sensors idle/spontaneous noise level. Raise the shadows too much, however, and you get mud.

[Steve Phillipps]

You guys want to be careful when altering these settings, really should be left to an expert, as tech guys have all sorts of measuring equipment that lets them know exactly what's going on. I'm very cautious when changing anything, just because it looks good on your particular monitor doesn't mean it will on anything, especially broadcast where you might find things have gone very wrong.
Steve

[Bob Grant]

Maybe I'm missing something here but I would have thought increasing black gamma will increase noise. You are adding gain at the bottom end of the curve where S/N is at its lowest. The dark current noise of the sensor is fixed by physics, not much can be done about it apart from cooling the camera.
On the other hand decreasing black gamma will crush the blacks and that's certainly not a look I'm fond of. However if shooting in low light with the gain up reducing the noise going into the encoder may yield benefits that outweigh the look of crushed blacks.

[Alister Chapman]

I've been thinking about this one and I need to go have a look at what actually happens. Certainly increasing gain will increase noise. I may have to eat my words!

[Paul Frederick]

This was recently posted in another thread...great info that may be of help. It explains crispening and black gamma quite well.

Sony | Micro Site - XDCAM EX

[Paul Kellett]

Originally Posted by Alister Chapman

I've been thinking about this one and I need to go have a look at what actually happens. Certainly increasing gain will increase noise. I may have to eat my words!

I did have a play with black gamma today.
Lowering (-) the black gamma did make the blacks blacker, as expected, sort of like lowering the normal black, it also appeared to lessen the noise in very dark areas.
I experimented in a room in my house, curtains shut, light off, 12db gain, although i looked on my camera screen, i haven't got a posh monitor.

If i'm shooting a wedding reception and i need to add gain then i can live with the blackest things staying black if it means no noise in those areas, ie black/dark dinner jackets, shadows under tables, dark hair etc.

If i'm reading the EX1 manual correctly then this is what the black gamma effects.


Thanks to everyone for chipping in, if we can come up with a less noisey PP for dark scenes
then i think we'd all be happy.

Thanks.
Paul.

[Bill Ravens]

it may be the case, and i just don't know for sure, that black gamma works more like a noise gate, setting it lower effectively shuts the door on any kind of signal, be it noise or not. Worst thing about these nebulous descriptions we get from Sony, who knows?

[Greg Boston]

Originally Posted by Bill Ravens

it may be the case, and i just don't know for sure, that black gamma works more like a noise gate, setting it lower effectively shuts the door on any kind of signal, be it noise or not. Worst thing about these nebulous descriptions we get from Sony, who knows?

Black Gamma is analogous to Black Stretch/Compress on other cameras. It is altering the shape of the bottom of the gamma curve.

-gb-

[Piotr Wozniacki]

Originally Posted by Greg Boston

Black Gamma is analogous to Black Stretch/Compress on other cameras. It is altering the shape of the bottom of the gamma curve.

-gb-

I agree with Greg, and compressing blacks has always been my preferred method of getting rid of some dark areas' noise (along with detail, of course - but I like that look, especially in low-light scenery; it's more "filmic" to me).

[Bob Grant]

What I think does work like a gate is "Black". From the description this is the same as what is known as Master Pedestal.
Anything above the Black level is then affected by Black Gamma.
Anything below the Black level is clamped to black.

The manual seems to recommend two adjustments to reduce noise. Black Gamma and Low Key Sat.

[Atilio Menendez]

Not only the black gamma is important here, also the general gamma curve.
Paul, which gamma curve are you using? I would recommend cine4. I think that using a "brighter" gamma curve is better than using a darker one (such as cine1) and applying gain to it. The camera achieves the brighter image on cine4 by applying gain in a non-linear fashion. It applies progressively less gain as it gets to higher values and thus protects your highlights from clipping. If you use cine1 and apply gain, gain is applied equally to all brightness values, thus clipping more of your highlights.

[Paul Kellett]

I'm using STD 1, hi sat, i like the punchier colours i get.

Paul.