Noise in photos and its causes

Rich · 16-10-2005, 21:41

Hi All,

I have noticed that more or less everytime i go out shooting i come back with a shed load of shots that are unusable due to noise, especially in dark areas, but often in light areas too.

For example, today i was in the Lakes, and ive come back with 80% noisy crap. The light was good, and the highest ISO i used was 400, but varied from 100-400.

What other considerations do i need to make to reduce noise in my shots?

Thanks!

CT · 16-10-2005, 21:48

Well you've described the causes Rich - high ISO and low light are the main causes of noise in your images. Noise will also be seen most in the darker part of your images.

I have to say I often use ISO 400 and usually don't find the noise that noticeable, in fact it can often resemble grain in film with modern digital cameras which isn't always unacceptable or unsightly.

Do you try running these shots through noise reduction software?

Rich · 16-10-2005, 21:59

thanks for the info. Yes i probably will try noise reduction software at some point, but the amount of noise im seeing is quite bad and id like to get things sorted before post process. I think i need to work on fine tuning exposure as well as this could be ruining things for me.

Cheers!

CT · 16-10-2005, 22:00

I suppose it's quite possible too that polarisiers and other filters needing an exposure compensation increase can contribute to noise, by cutting down light hitting the sensor and lengthening the exposure time.

CT · 16-10-2005, 22:01

Quote:

Originally Posted by Rich

thanks for the info. Yes i probably will try noise reduction software at some point, but the amount of noise im seeing is quite bad and id like to get things sorted before post process. I think i need to work on fine tuning exposure as well as this could be ruining things for me.

Cheers!

Well under exposure will lead to increased noise Rich. Can you post an example of one these shots?

Bachs · 16-10-2005, 22:07

The way to go if you have Photoshop CS2 is HDR (High Dyanamic Range).
You use several 'bracketed' shots across a wide dynamic range and use HDR to create a merged 32 bit file from which you can extract all of the range without introducing noise.
See tutorial here...
http://www.luminous-landscape.com/tutorials/hdr.shtml

16-10-2005, 22:12

Steve was telling me the other week about a forum he was reading which went into great detail about noise.
Apparently it got very very technical and geeky and went on to discuss frequencies etc etc.

Basically what they had found that (I forgot the details), but the jist of it was that the noise is there throughout the ISO range, irrespective of what ISO you're using, there's the same amount of noise in the shot at ISO100 as there is at ISO3200. It's when it becomes evident or something.
The upshot was, that if you trust your histogram, the trick to using high ISO's was to overexpose your image, obviously not blowing out the highlights (this is where trusting your histogram comes into play).
Then during the raw conversion process, you can drag the exposure compensation back down to return the shot to normal levels. Something like that.

Like I say though, it was mentioned over a 5 minute conversation, but Steve said either he'd taken or seen some pretty much noiseless shots at ISO3200.

Disclaimer : All of the above is from memory so could very well be factually incorrect, but the jist of it is true. At high ISO's, overexpose the shot. Also, I've slept since that conversation too, which is my brains reset button

Rich · 16-10-2005, 22:18

I was using a polariser today! Probably did have a large affect on it given the varying light levels (mountains = sunny in spots and masses of shadow in others).

Ill try and post an example when i go throught this lot

Ta.

***Steve*** · 18-10-2005, 10:46

Marcel has basically got the gist of it and its all new to me as well...what was being said in a very geeky manner and far beyond my technical knowledge is that if you shoot in raw, put all your in camera parameters (saturation, contrast etc) to the absolute minimum (minus settings) as they are only valid for JPEG photos and after the camera has “processed” the file, then over expose to the right but not past a recoverable amount. This increases the gain of the sensor and records as much detail from the shadow areas and from the blue channel (which actually is about 10 times less efficient than the others) giving you masses of detail to work with. It also virtually eliminates all the visible noise.

I was sceptical but when I was in Belfast Zoo with Stewart I altered my settings and gave it ago. The tricky part is getting the amount of over exposure just right as if you go too far to the right you will lose the highlight detail and blow out the picture beyond a recoverable amount. This happened to me on a couple of my shots but for the most time I managed to get it about right. If you are going to attempt this method of reducing the noise I would highly recommend practicing a lot first and on several different lighting situations, I did it on animals at the zoo as it didn’t really matter if I ruined all the shots as I had already recently managed to get some good animal photos from our Chester zoo trip.

Canon 20D, ISO 800, 1/1000sec, F5.6

Canon 20D, ISO 1600, 1/640sec, F5.6

and to show the blue channel noise

Canon 20D, ISO 800, 1/160sec, F5.6

All the above have just been processed in raw shooter and then resized, they have not been run through any noise reduction files.

Now if that doesn't start a discussion...

CT · 18-10-2005, 11:01

That's very interesting Steve - I'll have to give that a whizz!

So - are you saying the bulk of the noise is carried by the blue channel? (being less sensitive)

***Steve*** · 18-10-2005, 11:04

I am not saying that, tbh most of what I read was very technical and way beyound me but the bods who were discussing it were. What I did glean from the conversation is that apparently sensor noise is fairly constant and its only the lack of detail at higher iso's that allows it to become visible.

SammyC · 18-10-2005, 11:26

Got a link to that discussion? Being a computer bod (and there are others on here I suspect) we might be able to translate it!

BTW Steve, what does putting all the settings down to zero do if they only apply to Jpegs? Or did I miss something there?

***Steve*** · 18-10-2005, 11:55

no link at the moment..running on the lappy as the main rig is still packed from the trip over here. i will dig it out once I get sorted though.

Putting the settings down to minus figures best represent an unprocessed JPEG ie the closest you can get to a raw histogram which is what you need to work from to get the exposure as close as possible. The Histogram shown on the camera is extracted from your in camera settings for JPEG shooting even if you are shooting in RAW. This is done automattically by the camera so its the next best solution to giving the most accurate histogram for raw that we can get. Normally the difference wouldn't matter that much as we have lattitude when shooting raw but since we are aiming to use all that headroom, anything we can claw back is a benefit.

Mike Aiken · 18-10-2005, 12:21

Just a quick question guys,

At what stage of processing is it best to run a image through noise reduction software, and is there any adverse affect by doing it before you save your image for uploading to the site.

..........and can anyone point me in the direction of a link a simple to use "noise reduction software" site please?

Thanks

Mike

18-10-2005, 15:41

My workflow consists of the following :

Rawshooter
PSCS2
Minor absolutely necessary edits (rotate, etc)
Noiseware
Then I work on the image more if needed, although alot of my adjustments tend to be done in RSE if I can help it.

***Steve*** · 19-10-2005, 13:06

Quote:

Originally Posted by SammyC

Got a link to that discussion? Being a computer bod (and there are others on here I suspect) we might be able to translate it!

Took me a while but as promised…

Quote:

Most people assume that because the camera takes noisier pictures at higher ISOs in automatic mode with constant exposure compensation (or none), that noise is directly related to ISO, but this is not really true when you look at things from other perspectives. The signal-to-noise ratio in the sensor is the same, no matter what ISO setting you use, if you use the same f-stop and shutter speed on the same subject in the same light. Up until the point that the camera starts converting the analog voltages in the sensor to RAW numbers, ISO only affects one thing - metering. So, if you are managing the absolute exposure yourself, the ISO setting has no effect on the analog capture. Once the camera starts reading the sensor, then ISO makes a tremendous difference, because it causes a different range of sensor voltages to map to the numbers 0 through 4095. Given a specific absolute analog exposure on the sensor, you get the cleanest RAW data from the *highest* ISO that doesn't clip your highlights. This is not very useful information for high dynamic range images, like dark grey things in the shade and white things in the sun in the same image, but in medium- and low-contrast scenes, you can expose way to the right without blowing RAW highlights. JPEG settings don't affect RAW capture, but if you set the contrast to -2, your histogram become a bit more accurate for RAW data. Assuming that the WB setting is close to reality, white highlights generally clip in the 20D histogram just before the point where they clip in the RAW data.

Now if you want to read through all 4 pages of posts which go into far more detail than that small extract, then the whole thread can be found here. Be warned it gets quite heavy and is difficult to follow at times.

SammyC · 01-11-2005, 10:41

OK, I've read through the four pages of the thread, applied a large (LARGE) cup of tea to my brain and I think I've worked out what the heck they were on about.

If anyone is interested then I'll attempt to write it up and explain it (as I understand it) in non-technospeak.

16-10-2005, 21:41	#1 (permalink)
Rich Getting Comfy Join Date: Aug 2005 Posts: 152	Noise in photos and its causes Hi All, I have noticed that more or less everytime i go out shooting i come back with a shed load of shots that are unusable due to noise, especially in dark areas, but often in light areas too. For example, today i was in the Lakes, and ive come back with 80% noisy crap. The light was good, and the highest ISO i used was 400, but varied from 100-400. What other considerations do i need to make to reduce noise in my shots? Thanks!

16-10-2005, 22:07	#6 (permalink)
Bachs Forum Regular Join Date: Jul 2005 Location: Montrose NE Scotland Posts: 919	The way to go if you have Photoshop CS2 is HDR (High Dyanamic Range). You use several 'bracketed' shots across a wide dynamic range and use HDR to create a merged 32 bit file from which you can extract all of the range without introducing noise. See tutorial here... http://www.luminous-landscape.com/tutorials/hdr.shtml Last edited by Bachs : 16-10-2005 at 22:34.

18-10-2005, 10:46	#9 (permalink)
*Steve* Pixalo Crew Join Date: Jan 2005 Location: An Englishman living in Germany Posts: 16,158	Marcel has basically got the gist of it and its all new to me as well...what was being said in a very geeky manner and far beyond my technical knowledge is that if you shoot in raw, put all your in camera parameters (saturation, contrast etc) to the absolute minimum (minus settings) as they are only valid for JPEG photos and after the camera has “processed” the file, then over expose to the right but not past a recoverable amount. This increases the gain of the sensor and records as much detail from the shadow areas and from the blue channel (which actually is about 10 times less efficient than the others) giving you masses of detail to work with. It also virtually eliminates all the visible noise. I was sceptical but when I was in Belfast Zoo with Stewart I altered my settings and gave it ago. The tricky part is getting the amount of over exposure just right as if you go too far to the right you will lose the highlight detail and blow out the picture beyond a recoverable amount. This happened to me on a couple of my shots but for the most time I managed to get it about right. If you are going to attempt this method of reducing the noise I would highly recommend practicing a lot first and on several different lighting situations, I did it on animals at the zoo as it didn’t really matter if I ruined all the shots as I had already recently managed to get some good animal photos from our Chester zoo trip. Canon 20D, ISO 800, 1/1000sec, F5.6 Canon 20D, ISO 1600, 1/640sec, F5.6 and to show the blue channel noise Canon 20D, ISO 800, 1/160sec, F5.6 All the above have just been processed in raw shooter and then resized, they have not been run through any noise reduction files. Now if that doesn't start a discussion... __________________ .......__o .......\<, ....( )/ ( )

16-10-2005, 21:48	#2 (permalink)
CT Feet under the table Join Date: Mar 2005 Location: West Mids UK Posts: 3,500	Well you've described the causes Rich - high ISO and low light are the main causes of noise in your images. Noise will also be seen most in the darker part of your images. I have to say I often use ISO 400 and usually don't find the noise that noticeable, in fact it can often resemble grain in film with modern digital cameras which isn't always unacceptable or unsightly. Do you try running these shots through noise reduction software?

16-10-2005, 21:59	#3 (permalink)
Rich Getting Comfy Join Date: Aug 2005 Posts: 152	thanks for the info. Yes i probably will try noise reduction software at some point, but the amount of noise im seeing is quite bad and id like to get things sorted before post process. I think i need to work on fine tuning exposure as well as this could be ruining things for me. Cheers!

16-10-2005, 22:00	#4 (permalink)
CT Feet under the table Join Date: Mar 2005 Location: West Mids UK Posts: 3,500	I suppose it's quite possible too that polarisiers and other filters needing an exposure compensation increase can contribute to noise, by cutting down light hitting the sensor and lengthening the exposure time.

16-10-2005, 22:12	#7 (permalink)
Marcel Posts: n/a	Steve was telling me the other week about a forum he was reading which went into great detail about noise. Apparently it got very very technical and geeky and went on to discuss frequencies etc etc. Basically what they had found that (I forgot the details), but the jist of it was that the noise is there throughout the ISO range, irrespective of what ISO you're using, there's the same amount of noise in the shot at ISO100 as there is at ISO3200. It's when it becomes evident or something. The upshot was, that if you trust your histogram, the trick to using high ISO's was to overexpose your image, obviously not blowing out the highlights (this is where trusting your histogram comes into play). Then during the raw conversion process, you can drag the exposure compensation back down to return the shot to normal levels. Something like that. Like I say though, it was mentioned over a 5 minute conversation, but Steve said either he'd taken or seen some pretty much noiseless shots at ISO3200. Disclaimer : All of the above is from memory so could very well be factually incorrect, but the jist of it is true. At high ISO's, overexpose the shot. Also, I've slept since that conversation too, which is my brains reset button

16-10-2005, 22:18	#8 (permalink)
Rich Getting Comfy Join Date: Aug 2005 Posts: 152	I was using a polariser today! Probably did have a large affect on it given the varying light levels (mountains = sunny in spots and masses of shadow in others). Ill try and post an example when i go throught this lot Ta.

18-10-2005, 11:01	#10 (permalink)
CT Feet under the table Join Date: Mar 2005 Location: West Mids UK Posts: 3,500	That's very interesting Steve - I'll have to give that a whizz! So - are you saying the bulk of the noise is carried by the blue channel? (being less sensitive)

18-10-2005, 11:04	#11 (permalink)
*Steve* Pixalo Crew Join Date: Jan 2005 Location: An Englishman living in Germany Posts: 16,158	I am not saying that, tbh most of what I read was very technical and way beyound me but the bods who were discussing it were. What I did glean from the conversation is that apparently sensor noise is fairly constant and its only the lack of detail at higher iso's that allows it to become visible.

18-10-2005, 11:26	#12 (permalink)
SammyC Forum Regular Join Date: Jul 2005 Location: Bristol Posts: 1,466	Got a link to that discussion? Being a computer bod (and there are others on here I suspect) we might be able to translate it! BTW Steve, what does putting all the settings down to zero do if they only apply to Jpegs? Or did I miss something there?

18-10-2005, 11:55	#13 (permalink)
*Steve* Pixalo Crew Join Date: Jan 2005 Location: An Englishman living in Germany Posts: 16,158	no link at the moment..running on the lappy as the main rig is still packed from the trip over here. i will dig it out once I get sorted though. Putting the settings down to minus figures best represent an unprocessed JPEG ie the closest you can get to a raw histogram which is what you need to work from to get the exposure as close as possible. The Histogram shown on the camera is extracted from your in camera settings for JPEG shooting even if you are shooting in RAW. This is done automattically by the camera so its the next best solution to giving the most accurate histogram for raw that we can get. Normally the difference wouldn't matter that much as we have lattitude when shooting raw but since we are aiming to use all that headroom, anything we can claw back is a benefit.

18-10-2005, 12:21	#14 (permalink)
Mike Aiken Been here a while Join Date: Aug 2005 Location: Birmingham Posts: 417	Just a quick question guys, At what stage of processing is it best to run a image through noise reduction software, and is there any adverse affect by doing it before you save your image for uploading to the site. ..........and can anyone point me in the direction of a link a simple to use "noise reduction software" site please? Thanks Mike

01-11-2005, 12:26	#18 (permalink)
SammyC

18-10-2005, 15:41	#15 (permalink)
Marcel Posts: n/a	My workflow consists of the following : Rawshooter PSCS2 Minor absolutely necessary edits (rotate, etc) Noiseware Then I work on the image more if needed, although alot of my adjustments tend to be done in RSE if I can help it.

01-11-2005, 10:41	#17 (permalink)
SammyC Forum Regular Join Date: Jul 2005 Location: Bristol Posts: 1,466	OK, I've read through the four pages of the thread, applied a large (LARGE) cup of tea to my brain and I think I've worked out what the heck they were on about. If anyone is interested then I'll attempt to write it up and explain it (as I understand it) in non-technospeak.