Strange behavior of my XLH1a - Noise - Is it normal? at DVinfo.net

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Canon XL H Series HDV Camcorders
Canon XL H1S (with SDI), Canon XL H1A (without SDI). Also XL H1.


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Old October 17th, 2008, 11:43 AM   #1
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Strange behavior of my XLH1a - Noise - Is it normal?

Hi,

Recently I shot some low light images and after reviewing them, I noticed a great amount of noise / grain. I didn't remember the settings used so I did a little test. Nothing scientific.

I recorded a few seconds of a fixed object only lit with a flash light.
Settings:
No presset, factory default
Iris: f2.0
Gain: 0db
Shutter: 1/60
HDV 1080i

I attached a frame grab of this test and you can also download the movie file here:

http://sunens.uqac.ca/~jparchib/testgrain.m2t (original captured file)

http://sunens.uqac.ca/~jparchib/testgrain.wmv (wmv version)

Is it normal? Should I return the cam under warranty? Or should I send it to Canon for service? What do you think?

Thanks
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Strange behavior of my XLH1a - Noise - Is it normal?-applegrain.jpg  
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Old October 17th, 2008, 12:11 PM   #2
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I haven't had my hands on an XH in quite a long time so better advice might come from someone who shoots regularly with one. Since I'm at work, I only looked at the still grab and the WMV on a non-calibrated cheapo LCD. From that handicapped vantage point, it looks like some garden-variety gain applied to a low light shot, so I doubt your camera is defective.

Since there are separate switches for on/off of Automatic Gain and for Low/Med/High gain, is it possible that you set your gain, but had the AGC switch still in the "on" position? Even if you find too much gain after verifying that you're really shooting 0 or -3 gain, you can experiment with master pedestal, or even noise reduction settings, to mitigate "gain grain" in dark areas of the image.
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Old October 17th, 2008, 12:31 PM   #3
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Looks about right to me. Set your black level to crush if you want to squash that noise (or do it in post).
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Old October 17th, 2008, 09:12 PM   #4
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Thanks for your reply.

Pete: Correct me if I am wrong, but on the XL cams, the gain is set on a knob on the body. You set the AGC on or of or a gain value on the same control. When you set it to 0db (like in my test) it is 0db.

Daniel: Yes I am aware of differents things I can do to minimise the apparent grain or noise, but I was assuming that at 0db, I should get no grain at all, but at the moment, I can't get a flat black or dark grey with the default setting.

I'm new to HD but in the SD days, I was able to get a noise free picture with the XL2 at 0 db. Don't you agree guys?
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Old October 17th, 2008, 10:54 PM   #5
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Oops, sorry, you are quite right -- I misread it as an XH rather than an XL as I raced through "new posts" during my brief lunch break.

Yup, as long as you weren't using the Green box, spotlight, or night modes, your gain should be what was set on the XL H1a gain dial.

The gain grain assessment is the same, though. All the XH and XL cameras use the same sensor block and very similar processing. I do think grain is a bit more of a challenge for the XL and XH cameras as compared to the XL2. There are well over 3 times as many photosites on a CCD that's about the same dimensions as in the XL2 so there are fewer photons for each pixel at a given ambient light level, and with the much higher resolution of the HD cameras it is easier to notice the subtle grain in your footage. I use -3 whenever possible and even then sometimes there's just enough grain on certain shots that I'll tweak it in post.
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Old October 17th, 2008, 11:02 PM   #6
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Quote:
Originally Posted by Jean-Philippe Archibald View Post
I was assuming that at 0db, I should get no grain at all, but at the moment, I can't get a flat black or dark grey with the default setting.

I'm new to HD but in the SD days, I was able to get a noise free picture with the XL2 at 0 db. Don't you agree guys?
I just did a quick resample of your image down to SD resolution. Does that look more like what you were expecting?
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Old October 17th, 2008, 11:08 PM   #7
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I think the most objectionable aspect of the image is the compression. The custom presets will affect noise greatly. I find that -9 sharpening helps the most with noise and compression artifacts. (Noise is very hard to compress.)
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Old October 18th, 2008, 09:24 AM   #8
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Ok, thank you very much guys... I gess getting rid of the grain is a part of the learning HD curve.

What I want in fact is being able to shoot in the -3 0 +3 db range and get nices black or dark grey on the underexposed portion of the picture.

So you are suggesting to lower the sharpness and to crush the black?
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Old October 20th, 2008, 05:44 PM   #9
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Those noise characteristics look pretty normal to my eye.
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Old October 21st, 2008, 07:50 AM   #10
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If after corecting your settings you still think there's too much noise, there's a cool little plugin which can suppress a lot of noise. It's called Neat Video, made by the same people who created Neat Image (which I often use to correct noise with digital photos). Only problem is that it only works on PC right now...

You can get a demo here : Neat Video :: download

I use it with my XL2 when I gotta shoot at +6Db and higher, and it does a wonderful job cleaning mushy video noise without loosing any sharpness at all.

Hope this helps!
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