Is there a technical reason I am getting a lot of noise in this shot?

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burrachaga

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colin
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hi everyone,

i took this tonight of a friend kitesurfing and I was amazed at how much noise there was in the sky. You probably cant see it in the photo below because of the low res and also because i have put a little noise reduction on it but i was wondering if there is a technical reason why there should be so much noise in a shot like this? I have noticed it in a few of my shots recently where there has been a very strong blue sky, could this be a reason? is it because it is a high contrast shot?

there were no filters used but i had changed to using a 'vivid' setting. I have pulled some detail out of the shadows but the noise is huge in the raw file before any processing. I took some landscape shots whilst abroad last week and once again i noticed plenty of noise in a blue sky, any thoughts on what i might be doing wrong would be greatly appreciated.

shooting info

manual
f10
1/2500
iso 200
at 18mm on my 18-70
wb - direct sunlight
-0.3 exposure

 
Must say, the D300s is quite poor when it comes to blue skies too...

EDIT: Lovely shot there though!
 
Crop that in portrait style and it'll be a killer.
 
thanks for the nice comments.

I promise i am not just being nit picky and pixel peeping. I got the landscape pics back from the printer the other day at 18x12's and there was definately a little noise in the sky on the prints. i didnt run those shots through noise reduction because i thought it wouldnt show on a print but now this shot from tonight has even more noise on it than them. the noise prob wouldnt show after some NR but should i really have to use NR at iso 200!!
 
I think it's just something inherent with some Nikons. As I say, the D300s suffers the same problem, and has certainly been documented on the internet.

Maybe you'll find similar evidence on the D90...
 
burrachaga said:
thanks for the nice comments.

I promise i am not just being nit picky and pixel peeping. I got the landscape pics back from the printer the other day at 18x12's and there was definately a little noise in the sky on the prints. i didnt run those shots through noise reduction because i thought it wouldnt show on a print but now this shot from tonight has even more noise on it than them. the noise prob wouldnt show after some NR but should i really have to use NR at iso 200!!
Click to expand...

Can't see any noise. Maybe it's the printer?
 
Not sure why people are doubting the OP. A simple internet search will reveal the problem.
 
The blue channel has been the noisiest on digital cameras as far back as I can remember (the ealy-mid 90s)
 
After a little reading it seems Oli and Musicman are spot on. the d90 and d300 do seem to have problems with noise in the blue channel which for some reason is where the noise will show up first.

I also read that using 'vivid' could be the culprit for most of it so that is the next thing to try on my list.
 
burrachaga said:
the d90 and d300 do seem to have problems with noise in the blue channel which for some reason is where the noise will show up first.
Click to expand...

That is true in my experience of the D300 as well.

I like my old D200 for landscape stuff, doesn`t seem to suffer this problem.....:shrug:
 
Never heard of the D90 with that issue, but the D300 does "suffer" from it a lot - does seem to be mainly blue skies though.

Its colour noise rather than the usual sort though and I suspect its all to do with the various compromises you have to make to tune the sensor for a wide range of ISO performance - something has to give.

Does it bother me? Nope not at all, if my D300 died today I'd be straight out and buy another.
 
It's a great picture, and while I don't shoot Nikon I am curious about the noise issue you have raised. Judging from the lighting in that scene I would imagine you have pulled up the shadows more than just a little. Also, which raw processor did you use? Software choice and processing choices can significantly influence things like noise. You should look at your sharpening parameters too. If you don't mask off plain areas then sharpening algorithms will treat each pixel of noise as something that needs sharpening. I use Lightroom for my raw processing and one adjustment I commonly make is to add a stiff dose of masking to the sharpening controls. You do not want to sharpen the sky, only the edges of things and texture details.
 
I agree with Tim. Although I sharpen in PS I always mask out the areas I don't want sharpened.
 
p.s. If you can make the original raw file available somewhere it would be interesting to take a closer look and see what can be done. It can be a little hard to give precise comment on "technical reasons" for things without knowing exactly what you were working with in the beginning.
 
Having done a little digging the culprit here is, in fact, likely to be the red channel.

Blue and Red channels tend to suffer more noise than the Green with a Bayer sensor because a Bayer array has RGBG components - i.e. twice as many photosites are devoted to capturing green light than either of the other channels. This is because the human eye is more sensitive to detail in green light than red or, even less, blue.

When a Bayer sensor is exposed to a blue sky, then, the sensor collects half as much information about the redness and blueness of the sky than it does the green.

Because of the way that these values are stored digitally, there is more information available in the lighter tones for each channel. We're all quite accustomed to seeing noise in the dark portions of an image for this reason and it is the basis of the Expose-to-the-right (ETTR) method of calculating exposure. Dark areas are subject to more noise.

Consequently, in a blue sky, the green values benefit from the sensor having twice as much information to work with. The blue channel benefits from having high tonal values (lots of blue) which is good from an ETTR perspective. The red channel, however, is quite dark in comparison - there's very little red light and the result is effectively shadow noise in the red channel.

Boosting the saturation with a 'vivid' setting will only exacerbate the problem.

If you're looking to minimise it in PP, then you may be best off applying noise reduction to the red channel.
 
thanks for everyone's input.

I shoot everything in raw so olypauls's comment has just made me realise the 'vivid' picture control doesnt affect the image at all. I think the image i see on the back of the camera is a jpeg so that is affected but obviously the raw file is unaltered.

I haven't pulled much detail out of the shadows at all, or added much sharpening. the only bit of pp was to add a graduated filter to the sand to increase its brightness slightly. I would be happy for anyone to see the raw file for general interest but ive no idea how i could do that. i could put an 800px pixel pic on here without any editing if that would help (which would show my pp) but i dont think even that would show the noise at such a low res. I prob have to go to a 50% crop before the noise becomes evident but if i want to print this at 18x12 then the noise is going to show up.

A bit of Noise Reduction isnt a problem to add but i was just surprised that this colour noise would be an issue at iso 200.

I think it is just one of those things, it isnt a big deal really and as i said a bit of NR isnt hard to add now i am aware as to the reasons.

lastly, i use capture NX2 for most of my processing and i think it gives the best results for my NEF files but i dont think it allows me to individually alter the noise on each colour channel so i might have to go through my CS3 as well in the future.
 
You could upload a raw file to http://rapidshare.com/ for free and then post a download link back here. I think for the free service a file can only be downloaded ten times max, but that should be enough for someone to take a closer look and offer an opinion. I'm happy to look, but I would use Lightroom to open the file, since that's all I have.
 
Gel said:
Crop that in portrait style and it'll be a killer.
Click to expand...

crop yes but more square



Uploaded with ImageShack.us

apologies for ruining your 35mm shot...this is one which i feel the 3 elements are forming a square impression
 
I should start another thread on this but after doing a lot more printing over the past few months i have found it has totally changed how i crop things.

this is my theory!

because most of the images we view on the internet are quite small it used to make me crop all my photos quite hard to make the subject stand out more. Since printing many shots at 16x12 and bigger, i now quite like giving the subjects a bit more space. they can sometimes look a little cramped without any environment. I run a little blog for friends and family and if i dont crop the photos hard then people cant see the subjects very well, i have also found that many landscape shots look awful in small images but once printed at a decent size they look a completely different picture.

anyway, i think this shot would still need the shadow so this would be my harder crop and i should also straighten the slight distortion on the horizon!

 
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