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-   -   Canon A1 Problem - Help judge this footage (https://www.dvinfo.net/forum/canon-xh-series-hdv-camcorders/93474-canon-a1-problem-help-judge-footage.html)

Paulo Salomao May 7th, 2007 07:46 PM

Canon A1 Problem - Help judge this footage
 
5 Attachment(s)
Hello there,

I just got my Canon A1 a couple months ago and had the chance to use in a shoot. I rented a second one for that shoot from the same store I bought mine.

At the shooting day, my DOP and I looked at both and thought the image to be a bit weird when indoors. I have placed here screenshots of the high res images of the footage both indoors and outdoors.

The settings are all original from manufactory. Only one image has Steven's preset which helps a bit but you will notice the grain is still there.

Should I bring my camera back to Canon? Is anyone experience this same problem or am I doing something really wrong?

Thanks for the help!
Paulo

Khoi Pham May 7th, 2007 07:56 PM

Turn off the freaking auto gain.

Chris Barcellos May 7th, 2007 08:06 PM

Agreed. Turn of auto gain. It only took me about six months to realize my FX1 was pumping autogain, when I thought it was off. I think A1 works the same way, you have to select a gain level with one of the switches, and make sure that gain level is set at 0. Otherwise, the camera adds gain even though you think you are adjusting without it... grain shows.

Bill Busby May 7th, 2007 08:07 PM

Yea, what Khoi said.

Paulo Salomao May 7th, 2007 08:09 PM

Indeed. I can't believe I didn't figure that out.

So I believe in very dark situations its worth it to have the gain on?

Doug Lange May 7th, 2007 08:30 PM

I have mine set to: L-0, M-+3, H-+6.

Experiment. You may prefer L-0, M-+6, H-+12. However, +12 isn't great.

Khoi Pham May 7th, 2007 08:45 PM

Quote:

Originally Posted by Paulo Salomao (Post 674506)
Indeed. I can't believe I didn't figure that out.

So I believe in very dark situations its worth it to have the gain on?

It does not matter if you have your preset on 0db or what, the auto gain switch must be off, now if the light level is low, the first thing you want to adjust is your apperture, open that all the way, if it is still too dark then add 3 db gain, if it is still too dark then go to 6db and so on, gain should be the last thing you want to use because more gain=more grain, now if you don't mind about smooth video then you can also take your shutter speed down to 30th of a seconds or lower to gain more light. A1 is a manual camera, it is not a good auto camera.

Maksim Yankovskiy May 7th, 2007 09:45 PM

Yep, gain is artificially increasing sensitivity of the sensors by applying higher currents/voltages. Gain is "digital". In a way, gain to the sensor is what digital zoom is to the range - it tries to create more out of less. Aperture is what optical zoom is to the range - it increases the amount of light that is hitting the sensor. Open up the aperture (use lower F-number), or slow down the shutter speed - that comes with the price of motion artifacts, but you can lower the shutter speed from the usual 1/60 (if you are shooting 60i) without introducing much artifacts by setting your shutter speed to 1/48 and shooting in 24f mode.

Quote:

Originally Posted by Khoi Pham (Post 674520)
It does not matter if you have your preset on 0db or what, the auto gain switch must be off, now if the light level is low, the first thing you want to adjust is your apperture, open that all the way, if it is still too dark then add 3 db gain, if it is still too dark then go to 6db and so on, gain should be the last thing you want to use because more gain=more grain, now if you don't mind about smooth video then you can also take your shutter speed down to 30th of a seconds or lower to gain more light. A1 is a manual camera, it is not a good auto camera.


Don Palomaki May 8th, 2007 08:58 AM

An arguably better analogy is gain is to video is like push processing is to film. Push process film and you see higher effective film speed and more grain, and perhaps other artifacts.

The signal read from the CCD is analog, a voltage based on the light intensity raching the CCD, the exposure time, and the (normally small) self-noise componets in the CCD pixels such as leakage and dark currents. Gain is analog amplification of the signal read from the CCD, and any variations in individual pixel sensitivity and leakage and dark current appears as a grain in the image. Increasing gain amplifies the differences between pixels making them more apparent in the image.

Note that slow shutter speeds also may increase certain aspects of this grain - the part attributed to the pixel leakage and dark current, but the effect may not be as pronounces as using equivalent amount of gain.

The best answer is to shoot with adequate light to keep the CCD operating in its optimum range. If light is a problem, you can improve the images with judicious use of gain, slower shutter speed, and custom presets in addition to aperture. Arriving at the best setting for a given shooting situation is a bit of an art.

Maksim Yankovskiy May 8th, 2007 12:16 PM

Gain
 
Don,

As I remember from my days of exposure at hardware designs of a high-end ultrasound system, there are two types of gain: analog and digital. The difference is at what stage the gain scheme gets applied to the signal. The analog is applied at the signal after is read from a sensor, but before the signal passes through ADCs.

It sounds that what you describe above is the analog gain. The manufacturers usually apply both types of gain - analog and digital - but for the purpouse of knobs and switches call the same - gain. It's quite often that the digital gain is the bigger component, as analog aplifiers are much more expensive.

Don Palomaki May 8th, 2007 07:03 PM

The XL1 and GL1 both use analog gain for both image gain and white balance. I suspect that the A1 does also. Does anyone know for sure?

6 dB of gain is a one-bit shift, but 3 dB (1/2 bit?) would not be as easy digitally. Digital is likely used for many of the presets.


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