cleaner to gain down -3db?
 

Is it potentially cleaner to gain down -3db when shooting with this camera? I have some footage and I am sure the camera was set to 0db gain and auto gain was off (I was not shooting, I was being shot) and while most was very clean, some in relatively bright lighting conditions outdoors bright day, there are scenes that are very noisy, so I am curious if shooting -3db is a way to keep it a bit cleaner in shooting, assuming enough light natural or artificial of course.

Whats the downside to this?

Stephen Eastwood
http://www.StephenEastwood.com

i've run into this too and -3db didn't help. i don't think the exposure meter is very accurate. i've been "over exposing" by a notch or three and have gotten cleaner results. please try it and let me know if that's the case..or if it's just me.

i also import with an hv20 and monitor the source footage via hdmi/1080i/32"

the a1 is capable of some really clean images in bright and dark settings..so i'm sure the odd grain issues are exposure issues.

I'm usually shooting using Steve Dempsey's VIVGRB preset and -3db gain. I have only once come across video noise in almost all daylight recording situations be them full sun or cloudy. In particular I was filming elephants at a zoo with a painted brown post behind the animals. Everything about the shot is perfect except for sparkling pixels on the brown post. I don't have an explantion for it, but I don't think it is necessarily noise caused by any sort of gain influence.

Whenever I can get away with -3db I use it. I have seen extremely subtle sparkling on some thing I shot at +0db although rare and more like film grain....mostly on large flat coloured surfaces not unlike the brown post in the above example.

When using Steve Dempsey's VIVGRB Preset and 0 or -3 gain I found that there was a considerable abount of grain in the grean and red channel. I have not had the grain show up at -3 in any other Preset that I have used.

The only downides to -3db is the (obvious) loss of light, and the potentially less dynamic range. I don't know anyone who has measured the dynamic range of each gain setting independantly, and I suspect that 0db has very slightly greater lattitude.

Noise can be caused by a warm sensor (30+ minutes of shooting), narrow spectrum light (tungsten), or dark scenes (low key).

James, YES! What I'm speaking of is more like a film grain...and I really don't like it.

The 0 dB gain setting was probably arrived at based on using the optimal portion of the light sensitivity range of the CCD. The sweet range in the CCD transfer function of converting light to electricity. Using -3 dB gain effectively pushes the noise floor of the CCD down 3 dB. That is generally good. But in the process it also cuts 3 dB off the high end (bright light) headroom of the light-to-electricity conversion curve of the CCD, which might introduce other artifacts under certain scene conditions; e.g., possibly more susceptibility to vertical smear from bright point sources of light and other non-linear behaviors. You have to judge whether or not -3 dB works for you.

Could the noise using VIVIDRGB be caused by the +25 Color Gain setting?

Certainly might play a role....in particular the worst (and really only) time I have noticed any problems with the -3/VIVIDRGB combo is the one brown painted post I mentioned earlier. Being brown it may have hyped up the red CCD on the camera a bit and acted up. Generally -3 works very cleanly for me.

So your seeing noise/grain, but is it very often? Or just in some very unique situtations. I don't see the corelation between exposure and noise. Can you explain your thoughts on this?

It’s not very often.

I wish I could explain it. At least then I could identify the issue and solve it.

Frankly, it’s no worse than what can be seen on any HD broadcast…. and I am a bit OCD when it comes to a “clean” image

Slower shutter speeds can result in more visible grain thanks to the longer integration time for the dark current of the individual pixels.

James - How is the overall brightness of your video at -3?

I tried using the VIVIDRGB preset earlier today, the image was really bright. I tried using the nd filter which darkened the image and really brought out the colors, but there was considerable noise.

Perhaps not using nd and instead lowering the gain to -3 might improve things. So far with this camera, whether day, night, auto, manual, I have some degree of noise. I love my camera, but I'll love it more if I can get rid of the noise.

[QUOTE=Scott Becker;722638]James - How is the overall brightness of your video at -3? [QUOTE]

In daylight situations I have no issues with the brightness of the video. Generally I'm trying to stay in the sweet spot of the lens aperture at around f4-5 and shutter speeds of 60fps. Depending on the amount of available daylight this may need none, one or both ND filters with a gain of -3 to achieve a suitable exposure.

IMO the XHA1 has very low noise levels and I certainly don't have any issue with the camera.

I shoot in bright light on the water and found that the camera ND is much better then ND add on filters. I purchased a .6 and 1.2 Formatt ND filters and Hoya Pro1Digital filters ND x4 and NDx8 and did not like the results. Also when I have both ND camera filters on and still have too much light to have the iris in the 3-5 range I put the shutter to 120 with excellent results.

As for the VIVID with grain I found cutting down the color gain to 15 helped and lowering the red gain also.

Now no grain unless I under expose trusing the camera meter. I all most always go one to two stops more open then the meter recommends and always use -3 gain while shooting outdoors.

Hope this helps.