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50D dark area noise/discolouration at ISO200

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Claus Mortensen

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This shot was taken with my 50D at shutter speed 1/400, aperture 8 and ISO 200 with a 17-55 f/2.8 lens.

I did not take the photo myself but as far as I'm aware it was taken center focused and recomposed.

Full picture:
http://picasaweb.google.com/cbmortensen/2009_01_31?feat=directlink

Crop:

http://picasaweb.google.com/lh/photo/Ut65t_KeTn44p00jfccITQ?authkey=OnO7tfuhm1g&feat=directlink

As you can see from the crop, there is a very high level of noise and banding on the face of my baby girl. Why is that?

I'm sure this is a "basic" question but I would appreciate any feedback you can give.

Thanks!
 
I can't see the banding from my LCD, but its underexposed. If I was taking the pic with that 2.8, I would have shot the pic at least 640IS0 at f2.8-f4.0. Once you correct the exposure, your problems are solved.
 
mailman88 said:
I can't see the banding from my LCD, but its underexposed. If I was
taking the pic with that 2.8, I would have shot the pic at least
640IS0 at f2.8-f4.0. Once you correct the exposure, your problems are
solved.
Click to expand...
--
Thanks for your reply.

I know that the photo is underexposes in the dark area (i.e. my daughter's face). I guess my question is rather - if it was focused and thus metered on her face, why does it come out that way in the final photo? And even if it were metered on the sunny background - why does it come out spotty (red dots and what I'd call banding) in the dark areas at ISO 200?

The camera was on auto-ISO when the picture was taken - hence ISO 200. Would spot metering in stead of evaluative metering have helped?

Thanks!
 
You really needed a flash to fill in the shadows as the camera exposed for the background, leaving the subject dark. It looks like you probably tried to bump up the brightness in Photoshop, thus increasing the noise that you see. Anytime you brighten an image, regardless of ISO, noise will increase. Try some noise reduction software such as neat image, noise ninja, etc. Should clean up just fine. And remember to expose correctly to avoid this problem.
Claus Mortensen said:
mailman88 said:
I can't see the banding from my LCD, but its underexposed. If I was
taking the pic with that 2.8, I would have shot the pic at least
640IS0 at f2.8-f4.0. Once you correct the exposure, your problems are
solved.
Click to expand...
--
Thanks for your reply.

I know that the photo is underexposes in the dark area (i.e. my
daughter's face). I guess my question is rather - if it was focused
and thus metered on her face, why does it come out that way in the
final photo? And even if it were metered on the sunny background -
why does it come out spotty (red dots and what I'd call banding) in
the dark areas at ISO 200?

The camera was on auto-ISO when the picture was taken - hence ISO
200. Would spot metering in stead of evaluative metering have helped?

Thanks!
Click to expand...
--
Steve
 
What you're seeing is not a problem witht the 50D but with the limitations of photography in general. You have a foreground subject that is in much less light than the background. If you want to expose the foreground subject properly you need to spot meter but then your background will be blown. The camera metering system provided a happy medium (and did a respectable job) but the background is still overexposed and the subject is underexposed which will always show some noise especially if you try to bring the levels up in post processing.

As someone else mentioned you need to use fill flash and you'll have a perfectly exposed background and subject with no noise.

Bob
--
http://www.pbase.com/rwbaron
My PBASE page is new and growing so please be patient.
 
You probably should have posted this in the beginners section. I can't see any banding, especially at this size. But rest assured... the 50D performs marvelously at iso 200, and like another poster said use a flash to balance your subject with the background in these types of situations.

--
'The truth is rarely pure and never simple' Oscar Wilde
 
what you want, I believe, is high speed sync flash . don't think most cameras built in flash are capable of high speed sync, mine isn't (at least not that I can find in settings)

with backlit portrait scene, try a dedicated TTL flash unit with high speed flash sync enabled and flash exposure comp of -1. use diffuser maybe if you are close to subject. this will bring up the tones of the foreground (and thus cleaning up the noise) without casting to much unnatural looking shadows. a wide aperture would make the shot look great also but you'll need high speed sync because camera will blink warnings if it can't stop down enough to avoid over exposing foreground when shutter speed is limited to sync speed. maybe you can adjust the ISO low enough in some cases but not always.

set aperture to f/4 or wider and choose an ISO that puts the shutter speed above 1/250 ( maybe use D lighting even though it might disable ISO 100 setting).

I think this would work better than f/8 and trying to expose this foreground against bright sky without fill flash.
Claus Mortensen said:
--
This shot was taken with my 50D at shutter speed 1/400, aperture 8
and ISO 200 with a 17-55 f/2.8 lens.

I did not take the photo myself but as far as I'm aware it was taken
center focused and recomposed.

Full picture:
http://picasaweb.google.com/cbmortensen/2009_01_31?feat=directlink

Crop:

http://picasaweb.google.com/lh/photo/Ut65t_KeTn44p00jfccITQ?authkey=OnO7tfuhm1g&feat=directlink

As you can see from the crop, there is a very high level of noise and
banding on the face of my baby girl. Why is that?

I'm sure this is a "basic" question but I would appreciate any
feedback you can give.

Thanks!
Click to expand...
 
1.) I can't see any problem with the face on my calibrated 22" CRT monitor.

2.) You put the camera through a torture test - dark indoor facial shot, which bright sunlight exterior - the worst thing you can do for any photo.

3.) The camera tried to compromise the exposure and did a pretty good job - the face is still very visible, while the background isn't blown out. I've seen a lot worse.

Remember, the camera can only do so much. Try to avoid situation with extreme brightness variations, because the camera is more limited than the eye.

If I take your crop, download it, and look at it highly magnified, I can see some blue blotches which happen to look like blue blood vessels. I wonder if the camera somehow picked up some normally invisible vessels (due to the edge lighting?) and made them more visible? Or maybe it's just an underexposed face blown up out of proportion.
 
This is really very simple. If you have banding or any other unacceptable image quality problems with the 50D at iso 200 then you have a lemon! Return it, or work on your skills. It really is this simple... because NO 50D owner with an once of experience will say that it performs poorly, especially at lower iso's!

--
'The truth is rarely pure and never simple' Oscar Wilde
 
This is a scene with more dynamic range than can be captured in a digital sensor.

This gives you two choices: A) burn the background and shoot for the faces in shadows, B) use FIll Flash to illuminate the people and save the background.
--
Mitch
 
--
Thanks for your comments everyone.

As I think I mentioned, I'm fully aware of the exposure problems with this picture - and I know the settings were extremely testing for the camera. My question was more about the sensor behaviour in the dark area - but I think that's been answered.

My 50D performs fine when under more forgiving lighting conditions, when using fill flash etc. so I'm not so worried that I have a dud on my hands.

Cheers
 
n/t
 
--
Mine does that too when I make a mistake and underexpose.

To help you realize it's not the camera, here are two shots, both at

F4 200 ISO first underexposed and brought up in raw, the 2nd one correct exposure. 100% crops on both.

Even on the one with correct exposure if you look in the dark areas where the light could not fall you can see some chroma noise.

Underexpose



Correct expose

 
My wife and I went to HK during our Xmas hols and enjoyed it a lot.



Cheers
 
your pics serve to recall our wonderful holidays :-)



Cheers
 
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