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Low ISO pictures with apparent noise

J

joemod

macrumors regular
Original poster
Jun 8, 2010
196
23
Athens, Greece
Greetings,

I recently noticed that many pictures that I took with my Canon 7D+Tamron 17-50 and include sky in the composition seem to have noise. By noise I mean that sky pixels' color seems to change abnormally. These pictures were taken with low ISO (100-200). I attach a 100% crop of one of those. Is this normal?
I would like to point out that although I attached a jpg the same "noise" appears in raw images viewed in both DPP and Preview.

Thanks in advance.
 

Attachments

  • sky-crop.jpg
    sky-crop.jpg
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if your that concerned about insignificant noise that can only be observed at 100% crop i would recommend you sell your 7D and whatever glass you own, put the money towards a film camera and then only shoot b&w @ ISO 400...

all jesting aside pixel peeping will only serve to cause pain and anguish in your life. think about this: in the time it took you to examine the photo for noise, come to a conclusion it was a problem and post on macrumours (and crop the photo and export and upload etc) you could have gone out and take many many more picture of the sky, leaves, your pet(if you have one), people, anything! you could have edited your photo, or learned some Photoshop.

but i digress

up to iso 1600 on that camera noise is no issue, at all. period. end of story. yes it looks "noisy" however viewed at normal size or printed you wont notice any traces of precived "noise" what so ever.

disclaimer:
by no means am i trying to be overly critical and i am very sorry if you end up feeling hurt or what not by this post.
 
This is an issue with CMOS image sensors. I shoot with a T2i (which has the same CMOS sensor as the 7D) and have noticed this effect as well at ISO 100. If I had to guess, I would think that it is a thermal noise issue, where individual pixels register higher intensities due to temperature effects. This is hard for the camera to correct for. I've looked at some similar shots of the sky I've taken during the winter and summer taken at ISO 100, and the noise does appear to be higher in the summer shots. At -10˚C the noise is nearly non-existent.

Another consideration is that CMOS image sensors made for DSLRs are Bayer-patterned, meaning that they have more green pixels than red or blue (because our eyes are most sensitive to green). Because of that, the blue sensitivity of DSLRs is worse than green. This is very evident if you load a photo into Photoshop, go to Channels and select the Red, Green or Blue channel individually. You'll notice that the Green channel generally has less noise than Red or Blue.

Please read the following articles for more information:

http://en.wikipedia.org/wiki/Image_noise
http://www.cambridgeincolour.com/tutorials/image-noise.htm
http://www.cambridgeincolour.com/tutorials/camera-sensors.htm
http://micro.magnet.fsu.edu/primer/digitalimaging/cmosimagesensors.html
 
Native Iso

The 7d, 5d, etc get the most dynamic range with iso 200, 400. 800, 1600.

If you want less noise, with a slight hit to dynamic range, do iso 160, 320, 640, 1250.

Iso 100 is stupid and sucks.

Noise is always worse in dark areas of the frame, so shooting at a high iso in daylight is usually fine.
 
Fandongo said:
The 7d, 5d, etc get the most dynamic range with iso 200, 400. 800, 1600.

If you want less noise, with a slight hit to dynamic range, do iso 160, 320, 640, 1250.

Iso 100 is stupid and sucks.

Noise is always worse in dark areas of the frame, so shooting at a high iso in daylight is usually fine.
Click to expand...

In theory you may be right, I've heard this before but in reality nobody is ever going to notice except the most dedicated of pixel peepers. It's much better to be out taking pictures than be worrying about things like this.
 
Fandongo said:
The 7d, 5d, etc get the most dynamic range with iso 200, 400. 800, 1600.

If you want less noise, with a slight hit to dynamic range, do iso 160, 320, 640, 1250.

Iso 100 is stupid and sucks.

Noise is always worse in dark areas of the frame, so shooting at a high iso in daylight is usually fine.
Click to expand...

ISO 100 is the base ISO on Canon cameras. You are probably thinking of Nikons, which mostly start at 200 (the D7000 being a notable exception). Also, those fractional ISOs you mentioned will produce more noise because they are generated by the camera's internal software; they are not true ISO stops (they are pushed or pulled from the full stops).

'The full stop ISOs ( ISO 100, 200, 400 and 800 ) are implemented with hardware gain settings (in the sensor). But the ones in-between and 50/1600/3200 are implemented through software. The full stop ISO has lower noise than the in-between ones.'

Edit: adding some links...

Here are some useful links on the subject.

On the artificiality of fractional ISOs:

http://www.pages.drexel.edu/~par24/rawhistogram/40DTest/40DTest.html

With the 40D, the difference between full and fractional stops was quite noticeable (best to avoid the fractional ones).

The difference is also quite pronounced with the 1DsIII (again, the fractional stops are noticeably worse):

http://www.northlight-images.co.uk/article_pages/cameras/canon_1ds3_noise.html

But the difference between full and fractional stops on the 7D is apparently so nominal that this tester decided it would be OK to keep the option for fractional stops turned on:

http://www.northlight-images.co.uk/article_pages/cameras/canon_7d_noise.html

The 7D will show noise in dark areas at 100 ISO (all the more so if you increase the exposure or fill lighting in post-processing software), but changing the ISO for the very same shot to some higher, fractional amount won't result in less noise.
 
Last edited:
You may have underexposed the sky, which would result in the noise you see.

A properly exposed ISO 100 image from a 7D should have less noise than that based on the copies I've seen.
 
I can't remember where I read it, but I do remember reading an article on ISO that basically said darker areas are more noisy..which I guess we all know...

...but he went on to explain (with some complicated maths and stuff) because of the noise is dark areas, if you increased the ISO to 'expose to the right' (even if you then darkened it in post) you could end up with less noise than if shot a darker shot with a lower ISO.

In other words a dark shot at 100 ISO could be more noisy than the same shot shot at 200 ISO (because the 200 ISO shot is much brighter).
 
Isn't this sort of thing sometimes due to the colour information of the file exceeding the gamut of the monitor?

(Which would explain why the photos tend to look fine when printed, and why it's visible in both RAW and JPG files onscreen.)
 
telecomm said:
Isn't this sort of thing sometimes due to the colour information of the file exceeding the gamut of the monitor?

(Which would explain why the photos tend to look fine when printed, and why it's visible in both RAW and JPG files onscreen.)
Click to expand...

Displays have a far larger color gamut than prints do. Noise typically appears when an image is underexposed and I'd guess that's what happened here, but we don't have enough information to know that.
 
chrfr said:
Displays have a far larger color gamut than prints do. Noise typically appears when an image is underexposed and I'd guess that's what happened here, but we don't have enough information to know that.
Click to expand...

My understanding was that each (printers vs monitors) excelled with a different range of colours, and that some colours printed well but didn't display well, and vice versa. For example, cyan is one colour that is typically better in print (CMYK) than on a monitor (RGB). Link
 
telecomm said:
My understanding was that each (printers vs monitors) excelled with a different range of colours, and that some colours printed well but didn't display well, and vice versa. For example, cyan is one colour that is typically better in print (CMYK) than on a monitor (RGB). Link
Click to expand...

That can be true in very limited cases, with printers that use more than 4 colors but in general CMYK is a vastly smaller gamut than RGB. Take a trip to /Applications/Utilities and open the ColorSync Utility. Take a look at the representations of Adobe RGB and a CMYK profile such as the generic one, or US Web Coated (SWOP) if you have any Adobe software installed. That will give you a good comparison of the color gamut sizes.
Edit: in any case, the noise in that image has no relationship to color gamut. Out of gamut colors will appear as banding, not random noise.
 
TheDrift- said:
...but he went on to explain (with some complicated maths and stuff) because of the noise is dark areas, if you increased the ISO to 'expose to the right' (even if you then darkened it in post) you could end up with less noise than if shot a darker shot with a lower ISO.

In other words a dark shot at 100 ISO could be more noisy than the same shot shot at 200 ISO (because the 200 ISO shot is much brighter).
Click to expand...

Yes, it's true. I habitually expose to the right, so I have a lot to say about the practice (usually known by its acronym ETTR). If you want to minimize noise in dark areas, it's best to expose to the right. There is a lot of confusion about what ETTR actually means, however. Some people think it means overexposing the photo, which is not quite correct. It simply means exposing so that all channels on the histogram are as far to the right as possible *without clipping any one of them*. And since all current DSLRs show you histograms of your JPEG preview (instead of your raw data), it's best to use UniWB in combination with ETTR (UniWB = Unitary White Balance, a custom WB profile made to display your raw data as accurately as possible).

As for a higher ISO being better when shot "to the right":

• versus a lower ISO shot that was underexposed and then pushed in post (significantly, probably more than a whole stop), yes the higher ISO shot will have less noise.

• versus a lower ISO shot that was exposed exactly how it should look, with no changes necessary, it will probably be a tie.

• versus a lower ISO shot that was also exposed to the right, the lower ISO shot will have less noise.

So to summarize for the 7D...if you want the least possible amount of noise in your shadows:

1) Use the lowest ISO you can, down to 100 (ISO 50 is a software fudge.)
2) Expose as far to to the right as you can without clipping any single channel. (And use UniWB to avoid unexpected clipping.)

I should also note that ETTR will help you to maximize your dynamic range and color depth as well.
 
This is a pretty interesting discussion. Many of my Canon shooting friends have said something similar. Maybe it is a characteristic of the camera. I shoot with a Nikon D3s and have virtually ZERO noise issues, even shooting way up around 8000 or so, even up to 10000 without any real noise problems. I will keep an eye on this for the future. Great info put out here.
 
@all thanks for the replies.

@Hansolo669. you did not hurt my feelings. going offtopic to answer your questions(select the text following).
What would you have done if you noticed that apparently something was wrong with your camera? Wouldn't you have asked a forum where knowledgable people reside? Also I post the question at 1.30 am. There wasn't any reason to go outside and take pics of sky or people in one of Athens' dangerous neighborhoods. Finally the crop was from one of the pictures I shot in Cairo, Egypt. I viewed it at 100% to enjoy it more. I 'll post one of them in POTD thread
 
sapporobaby said:
This is a pretty interesting discussion. Many of my Canon shooting friends have said something similar. Maybe it is a characteristic of the camera. I shoot with a Nikon D3s and have virtually ZERO noise issues, even shooting way up around 8000 or so, even up to 10000 without any real noise problems. I will keep an eye on this for the future. Great info put out here.
Click to expand...

It is something that people on the airliners.net site used to complain about endlessly with the Canon 7D. It's only an issue at 100% and it's not particularly bad - only when you pixel peep. Resize down and that noise will not be there. I wouldn't worry about it much at all. I'd prefer to get a sharp and well exposed image first, rather than worry about noise.

Photoshop CS5 Camera Raw can clean up that slight noise very easily if required.
 
Phrasikleia said:
ISO 100 is the base ISO on Canon cameras. You are probably thinking of Nikons, which mostly start at 200 (the D7000 being a notable exception). Also, those fractional ISOs you mentioned will produce more noise because they are generated by the camera's internal software; they are not true ISO stops (they are pushed or pulled from the full stops).

'The full stop ISOs ( ISO 100, 200, 400 and 800 ) are implemented with hardware gain settings (in the sensor). But the ones in-between and 50/1600/3200 are implemented through software. The full stop ISO has lower noise than the in-between ones.'

Edit: adding some links...

Here are some useful links on the subject.

On the artificiality of fractional ISOs:

http://www.pages.drexel.edu/~par24/rawhistogram/40DTest/40DTest.html

With the 40D, the difference between full and fractional stops was quite noticeable (best to avoid the fractional ones).

The difference is also quite pronounced with the 1DsIII (again, the fractional stops are noticeably worse):

http://www.northlight-images.co.uk/article_pages/cameras/canon_1ds3_noise.html

But the difference between full and fractional stops on the 7D is apparently so nominal that this tester decided it would be OK to keep the option for fractional stops turned on:

http://www.northlight-images.co.uk/article_pages/cameras/canon_7d_noise.html

The 7D will show noise in dark areas at 100 ISO (all the more so if you increase the exposure or fill lighting in post-processing software), but changing the ISO for the very same shot to some higher, fractional amount won't result in less noise.
Click to expand...

http://photocascadia.wordpress.com/2011/05/13/canon-eos-5d-mark-ii-iso-noise-test/#

His conclusion states (abridged):

On visual inspection it is easy to see that, sure enough, the ISO settings in one stop increments starting at ISO 160 (160,320,640, 1250, etc.) have the least noise and the one stop increments starting at ISO 125 (125, 250, 500, 1000, etc.) have the most noise with the multiples of ISO 100 being somewhere in between.
Using jpg file size to rank noise levels the ISO settings can be arranged from best to worst as follows:

160, 320, 100, 200, 640, 400, 125, 250, 800, 500, 1250, 1000, 1600, 2000, 2500, 3200, 4000, 5000, 6400, 12800

The differences among ISO 100, 160, 200, 320 and 640 are fairly minimal so all these settings should produce low noise images as far as the eye can tell. However, if shutter speed is of critical importance it is great to know that I can shoot at ISO 320, almost two stops faster than ISO 100, and actually get better image quality than ISO 100. ISO 640 is only marginally more noisy than either ISO 100 or 200 and significantly better than ISO 125. In fact, the test shows that ISO multiples of 125 should really just be avoided all together.

At the higher end of the ISO spectrum noise begins increasing more as you would expect. While ISO 1250 is still better than 1000 and almost as good as 800, at ISO 1600 and higher the multiples of 160 don’t offer much of an advantage. Noise at ISOs above 1600 becomes essentially unusable for most of my photography.



That, and i trust people like Shane Hurlbut, who use my camera/technicolor profile in Movieland.
The technicolor profile boosts the hell out of the blacks to flatten the image resulting in more noise.
Somehow the 160 intervals have slightly less even if they are digitally created.
If peaking highlights are more important, I choose 200, 400, 800.
I also use the gh2, where 320 and 640 isos are powerfully awful.

It all depends.
If you're really worried about your pixels, read everything you can, and test test test.
Or keep half a mind on it and work work work.
You can repair the hell out of a photo
But it's hard to edit a shot you didn't take!

Shoot on! =)
 
It's underexposed so it's very visible, but if you got the right exposure it shouldn't be visible. You could edit these easily in PS though.
 
steveash said:
In theory you may be right, I've heard this before but in reality nobody is ever going to notice except the most dedicated of pixel peepers. It's much better to be out taking pictures than be worrying about things like this.
Click to expand...

Much agreed, but if you're working on a multi-cam project with multi-cam people, it might help to give some guidelines.

It's more noticeable and harder to fix in 1080p :D
 
Can you imagine the images the world would be deprived of if photographers in the past had fretted over such nonsense such as noise/graininess or sharpness of the lens/body?

In a perfect world, all images would be 100% noiseless/grainless and 100% sharp. We do not live in a perfect world. If you want 100% predictability .... shoot a tried and proven media .... use film. I still shoot in film, when what I am shooting is something extremely important to me.

FWIW: I think that anyone who wants to be a photographer, even at the hobby level should find a local college that offers a course of PHOTOGRAPHY 101. But only if that course requires you to provide a MANUAL FILM CAMERA. There you will learn what it means to be a photographer and not just an appliance operator.
 
harcosparky said:
FWIW: I think that anyone who wants to be a photographer, even at the hobby level should find a local college that offers a course of PHOTOGRAPHY 101. But only if that course requires you to provide a MANUAL FILM CAMERA. There you will learn what it means to be a photographer and not just an appliance operator.
Click to expand...

I have to disagree. I had never touched a film camera in my life and wanted to be a photographer. Went to college and took Photo 101 first semester, developed a few rolls and dropped out before I could even register for 102.

In the past 5 years I have not touched a single piece of film, but I have touched my digital cameras quite a bit.

Yet, somehow, miraculously, against all odds, I am making a living as a professional photographer, granted, I do tend to use M...

:rolleyes:

I get lots of clients asking me about if I shoot film and I tell them, honestly and in a nicer way, that shooting film is a stupendous drain on time and resources. Film cameras use older technology. Film is expensive. Film is risky. The end result is an inferior product for an inferior cost.

I do agree with the rest of your post though, on how technically "perfect" photographs are not the best. Clients often order the most prints of the shots I almost deleted due to missed focus, guys head in the way, whatever.

Sure, someday I would like to get a large format camera when funds allow to mess around with some landscapes, but in all honesty I do not see much benefit to film, especially for a new photographer. Time and money is much better spent taking 1st person shots of your shoes with a Rebel Xs.

:D
 
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