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Canon XL and GL Series DV Camcorders
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Old January 30th, 2005, 04:02 AM   #1
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XL2 Signal to Noise Ratio

Does anyone know what the signal to noise ratio on the XL2?

I've done some film work as a student, and on independent features, but this is my first foray into digital. I want to know the dv camera operation inside and out.

Canon does not seem to have released this information based on some moderate google searching.

Along these same lines, if anyone has any reccomendations for technical books on digital video, I'd love to hear them. I picked up a rather brutal book called "Digital Video and HDTV: Algorithms and Interfaces." I'd like to get something a half-step less technical so I have something to read when my brain starts bleeding.

Monty
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Old January 30th, 2005, 11:33 AM   #2
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It appears that you're right, about Canon not releasing the S/N ratio spec. I can't seem to find it either.

With regard to technical book recommendations, check out our Read About It forum, which ios where we discuss that exact topic. You'll find lots of good suggestions there! Hope this helps,
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Old January 31st, 2005, 12:12 PM   #3
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Gee - what is the rigorous definition of the SNR for a video camera? The SNR will change for various lighting schemes and camera settings. As a specification alone SNR is useless (as is lux rating, since it's meaningless without knowing aperture, gain and shutter speed).

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Old January 31st, 2005, 12:48 PM   #4
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Steve is right. It like asking what the RPM's are for a car going 60 miles per hour. There are a lot of variables.
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Old January 31st, 2005, 01:44 PM   #5
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At a given point

You'd have to know what the SNR is at any given point before you could know it for any other given point.

Monty
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Old February 3rd, 2005, 08:49 PM   #6
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Well here are some numbers but I'm puzzled by them. In 30p mode with 16:9 aspect ratio with the gain set at -3 dB the SNR is 49.1 dB; at 0 dB gain 49.5 dB; at 3 dB gain 47.8; at 6 dB gain 55.3 and at 12 db gain SNR is 45.43. What's puzzling is that the SNR is best at a gain setting of 6dB and by an appreciable amount. I suppose this might be explainable if we knew how the gain is distributed which, of course, we don't.

Here's how I got these numbers. With the lens cap on I captured a frame at each of the gain settings (using BTVPro) and then imported each of the images into an analysis program (IGOR Pro) with which I calculated the luminance for each pixel using Y=0.299R+0.587G+0.114B. I then computed the standard deviation over all the luminance values. This standard deviation represents the square root of the noise power as in a perfect camera the luminance would be a constant (the pedestal) for all values. 20*log(256/SD) is thus the SNR since the peak possible value is 256 in an 8 bit word (255 to be precise).

As these results are not what I expected I caution everyone to take them with a grain of salt until I get a chance to check my results. I'm putting this up now in the hope that someone else will make similar measurements.
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