Grains, pixels, and personal incompetence at DVinfo.net

Jeff Yin · August 28th, 2007, 07:35 PM

Let me preface this post with a broad disclaimer: User error is the single most likely source of these problems. That being said, I've run across a few unwanted visual effects in some of the test footage I've shot.

I was using the 5296 preset found in the sticky thread above, and the standard gain settings (though I didn't mess with the gain, so it should be at the lowest of the standard settings). Also, I was shooting in 24f. My fstop, zoom, and shutter speed changed from time to time, as I was experimenting with different settings.

When shooting inside, even during the day with bright sunlight, I seem to be getting a grainy image. I've searched on the forums and I've seen people suggest changing the gain settings to 0 or even -3db. Can anyone comment on whether that actually reduces gain? If it does, what do you give up and how do you compensate for it?

When shooting outside, I notice some pixelation, particularly on the borders of strongly contrasting colors, like a black shirt on a white person. Is this normal? If not, what can I do to correct it?

Finally, my footage looks much worse on an HD tv than a SD one. I assume that's because the HD TV is able to more accurately display my incompetence than an SD one. What settings concerns do you have to keep in mind specifically for HD?

Thanks!

David W. Jones · August 28th, 2007, 08:01 PM

You don't happen to have the AGC switch on the side of the camera set to ON do you?

Don Palomaki · August 29th, 2007, 06:24 AM

The grain effect is due in large part to slight differences in pixel dark current and sensitivity. It is most apparent in shadows areas of the image. Longer exposures can make dark current variations more apparent. Reducing gain has the effect of reducing the visibility of the differences in pixels. However, if reducing gain is accompanied by a corresponding slower shutter speed, the benefit may be reduced.

Jeff Yin · August 30th, 2007, 04:55 AM

I do not have AGC on. Should I?

Don Palomaki · August 30th, 2007, 06:26 AM

Quote:

Originally Posted by Jeff Yin

I do not have AGC on. Should I?

That is your decision. With AGC enabled, the camcorder controls the gain setting, and may increase gain in moderate-to-low light situations (or even in bright light situations if the ND filter is on) without your knowledge. This may make grain more apparent in the image. Many shooters prefer to manually control gain (and the other exposure parameters for that matter). You really need to work with the camcorder, experiment a lot, to see what works best for you in the different shooting situations you encounter.

Note that AGC is automatically ON in Night and Easy Recording modes, OFF with gain set to 0 dB in Spotlight mode, and can be on or manually adjusted in other recording modes..

Jeremy Naus · August 30th, 2007, 06:35 AM

no should not put agv on :-)

I experienced the same problem as you. My problem was that my LCD of the A1 was not properly calibrated out of the box.
I hooked it up to a tv screen and used that to calibrate it.
Since the LCD was displaying everything to bright I usually made my lense opening smaller and put the shutter to fast.
Once calibrated you should be able to reduce the grain by setting the lensopening and shutter speed to better values

Meryem Ersoz · August 30th, 2007, 06:39 AM

Quote:

Originally Posted by Jeff Yin

When shooting inside, even during the day with bright sunlight, I seem to be getting a grainy image. I've searched on the forums and I've seen people suggest changing the gain settings to 0 or even -3db. Can anyone comment on whether that actually reduces gain? If it does, what do you give up and how do you compensate for it?

you compensate by adding artificial light, either your light kit or maybe a good on-camera light. or blocking the ambient light and either opening the aperture or adding a small amount of gain. or getting a good artificial light set up. if you shoot indoors using only natural light, you're typically introducing a range of contrasts which the camera doesn't necessarily have the latitude to handle (e.g. you have to choose, am i going to blow the highlights to get someone face properly exposed, or am i wanting a more evenly exposed image, therefore i'll settle for more shadows. et cetera).

Bill Pryor · August 30th, 2007, 06:52 AM

If you were shooting at anything other than -3 or zero db, you're going to get grain. This is true with any camera. Shutter speed should be 1/48 for 24 fps, unless you're after an effect.

Jeff Yin · August 31st, 2007, 02:23 PM

Thanks for the settings advice. I've shot some test footage and it looks much cleaner than when I started.

Does anyone have any input for the pixelation problem I noticed on external/outside shots?

Jerome Cloninger · August 31st, 2007, 03:33 PM

Quote:

Originally Posted by Jeff Yin

Does anyone have any input for the pixelation problem I noticed on external/outside shots?

You might get better help if you post a pic or clip of the problem!

August 28th, 2007, 07:35 PM	#1
Jeff Yin Regular Crew Join Date: Aug 2007 Location: Fremont California Posts: 27	Grains, pixels, and personal incompetence Let me preface this post with a broad disclaimer: User error is the single most likely source of these problems. That being said, I've run across a few unwanted visual effects in some of the test footage I've shot. I was using the 5296 preset found in the sticky thread above, and the standard gain settings (though I didn't mess with the gain, so it should be at the lowest of the standard settings). Also, I was shooting in 24f. My fstop, zoom, and shutter speed changed from time to time, as I was experimenting with different settings. When shooting inside, even during the day with bright sunlight, I seem to be getting a grainy image. I've searched on the forums and I've seen people suggest changing the gain settings to 0 or even -3db. Can anyone comment on whether that actually reduces gain? If it does, what do you give up and how do you compensate for it? When shooting outside, I notice some pixelation, particularly on the borders of strongly contrasting colors, like a black shirt on a white person. Is this normal? If not, what can I do to correct it? Finally, my footage looks much worse on an HD tv than a SD one. I assume that's because the HD TV is able to more accurately display my incompetence than an SD one. What settings concerns do you have to keep in mind specifically for HD? Thanks!

August 29th, 2007, 06:24 AM	#3
Don Palomaki Wrangler Join Date: Sep 2001 Location: Northern VA Posts: 4,487	The grain effect is due in large part to slight differences in pixel dark current and sensitivity. It is most apparent in shadows areas of the image. Longer exposures can make dark current variations more apparent. Reducing gain has the effect of reducing the visibility of the differences in pixels. However, if reducing gain is accompanied by a corresponding slower shutter speed, the benefit may be reduced. __________________ dpalomaki@dspalomaki.com

August 28th, 2007, 08:01 PM	#2
David W. Jones Trustee Join Date: Dec 2006 Location: Little Rock Posts: 1,383	You don't happen to have the AGC switch on the side of the camera set to ON do you?

August 30th, 2007, 04:55 AM	#4
Jeff Yin Regular Crew Join Date: Aug 2007 Location: Fremont California Posts: 27	I do not have AGC on. Should I?

August 30th, 2007, 06:35 AM	#6
Jeremy Naus Regular Crew Join Date: Nov 2006 Location: Antwerpen, Belgium Posts: 60	no should not put agv on :-) I experienced the same problem as you. My problem was that my LCD of the A1 was not properly calibrated out of the box. I hooked it up to a tv screen and used that to calibrate it. Since the LCD was displaying everything to bright I usually made my lense opening smaller and put the shutter to fast. Once calibrated you should be able to reduce the grain by setting the lensopening and shutter speed to better values

August 30th, 2007, 06:52 AM	#8
Bill Pryor Contributor Join Date: Jan 2003 Location: Kansas City, MO Posts: 4,449	If you were shooting at anything other than -3 or zero db, you're going to get grain. This is true with any camera. Shutter speed should be 1/48 for 24 fps, unless you're after an effect.

August 31st, 2007, 02:23 PM	#9
Jeff Yin Regular Crew Join Date: Aug 2007 Location: Fremont California Posts: 27	Thanks for the settings advice. I've shot some test footage and it looks much cleaner than when I started. Does anyone have any input for the pixelation problem I noticed on external/outside shots?