Noise in High ISO

[GeckoZ]

Hi CS-er, I got a question on High ISO.

I've reviewed some of my photos taken last time and noticed that at 1600 ISO, when the photo was well exposed with enough light, the noise pollution wasn't so obvious. But if the photo was much underexposed, the noise is very bad and could easily tell.

So I'm I actually right to say that high ISO can be used, but you'll have to slow down the shutter speed and/or enlarge the aperture to make sure that your photo will be brightly exposed and will not turn out noisy (if noise is undesired)?

[dot1q]

Nope, its the other way around, once the ISO is increase the shutter speed also increase...
like other CS-er's always tell, once you up the ISO, you are pumping up more noise...

[ExplorerZ]

Originally Posted by GeckoZ Hi CS-er, I got a question on High ISO. I've reviewed some of my photos taken last time and noticed that at 1600 ISO, when the photo was well exposed with enough light, the noise pollution wasn't so obvious. But if the photo was much underexposed, the noise is very bad and could easily tell. So I'm I actually right to say that high ISO can be used, but you'll have to slow down the shutter speed and/or enlarge the aperture to make sure that your photo will be brightly exposed and will not turn out noisy (if noise is undesired)?

pretty right to say that... but do note that if you try increasing the exposure by reducing shutter duration, you are actually having the risk of camerashake/movement blur which defeats the purpose of shooting @ high ISO.

[GeckoZ]

Originally Posted by ExplorerZ pretty right to say that... but do note that if you try increasing the exposure by reducing shutter duration, you are actually having the risk of camerashake/movement blur which defeats the purpose of shooting @ high ISO.

This was what happened to me that needed me to increase both ISO and shutter speed to expose my photos better in low light situation:

I was shooting indoor without flash and tripod. without high ISO, my shutter speed would be much more longer and the risk of handshake and momvent blur is much higher, so what i did was increased my ISO to 800 and 1600 and able to shorten my shutter-open duration (altough the shutter speed is still slow, but atleast faster then when using a 100/200 ISO).

I noticed by comparing the pictures and found out high ISO with adequate exposure was pretty good, the noise level was not so obvious.

any idea what's the rational behind this "shutter speed-high ISO" thinggy? why is noise being absorbed more easily when light intensity is high as compared to "normal light", but when you prolong your shutter speed it will take in the "normal" light instead of noise?

[wildstallion]

Basically, ISO 1600 can be quite usable if exposed correctly. However, nosie will be noticable and detail will be lacking, shadows will be full of noise. Usually when people shoot in high ISO there is a lack of light, and therefore many underexposed parts, therefore noise is common.

[GeckoZ]

Originally Posted by dot1q Nope, its the other way around, once the ISO is increase the shutter speed also increase... like other CS-er's always tell, once you up the ISO, you are pumping up more noise...

hi dot1q, let's say i'm keeping the ISO constant at 1600 for 2 photos taken with a tripod. an underexposed photo with shutter speed 1/60 would appear more noisy then a photo taken at 1/8 well exposed. and the latter photo's noise pollution wasn't actually obvious at all.

[wildstallion]

Originally Posted by GeckoZ hi dot1q, let's say i'm keeping the ISO constant at 1600 for 2 photos taken with a tripod. an underexposed photo with shutter speed 1/60 would appear more noisy then a photo taken at 1/8 well exposed. and the latter photo's noise pollution wasn't actually obvious at all.

Because its properly exposed.

[GeckoZ]

Originally Posted by wildstallion Basically, ISO 1600 can be quite usable if exposed correctly. However, nosie will be noticable and detail will be lacking, shadows will be full of noise. Usually when people shoot in high ISO there is a lack of light, and therefore many underexposed parts, therefore noise is common.

Thanks wildstallion. Just a question, what causes the lack in detail, and does it only affect the shadow part or the overall photo?

I suppose sometimes you'll also need to pump up to high ISO when the lighting wasn't all that bad, but u just want to get your image real sharp and well exposed at, say, shutter speed 1/125 isn't it? so would that be fine?

[wildstallion]

Originally Posted by GeckoZ Thanks wildstallion. Just a question, what causes the lack in detail, and does it only affect the shadow part or the overall photo? I suppose sometimes you'll also need to pump up to high ISO when the lighting wasn't all that bad, but u just want to get your image real sharp and well exposed at, say, shutter speed 1/125 isn't it? so would that be fine?

Yeah, your right, but in general, a high ISO such is ISO800-1600 is for low light situations.

1/125 depends on the aperture, ISO and amount of light.

I believe detail is lost due to the CCD or CMOS censor being more sensitive to light, increasing its gamma, which in turn causes a lack in detail in areas of shadow and in areas of light. This coupled with a large aperture can make high ISO pics look unsharp.

[GeckoZ]

Originally Posted by wildstallion Yeah, your right, but in general, a high ISO such is ISO800-1600 is for low light situations. 1/125 depends on the aperture, ISO and amount of light. I believe detail is lost due to the CCD or CMOS censor being more sensitive to light, increasing its gamma, which in turn causes a lack in detail in areas of shadow and in areas of light. This coupled with a large aperture can make high ISO pics look unsharp.

Ok, got it! Thanks so much.

[ExplorerZ]

Originally Posted by GeckoZ hi dot1q, let's say i'm keeping the ISO constant at 1600 for 2 photos taken with a tripod. an underexposed photo with shutter speed 1/60 would appear more noisy then a photo taken at 1/8 well exposed. and the latter photo's noise pollution wasn't actually obvious at all.

well if you can handhold at 1/8... I don think you will have to use ISO1600 and 1/60... you can simple go for 1/15 at ISO200 instead.

[dot1q]

Originally Posted by GeckoZ This was what happened to me that needed me to increase both ISO and shutter speed to expose my photos better in low light situation: I was shooting indoor without flash and tripod. without high ISO, my shutter speed would be much more longer and the risk of handshake and momvent blur is much higher, so what i did was increased my ISO to 800 and 1600 and able to shorten my shutter-open duration (altough the shutter speed is still slow, but atleast faster then when using a 100/200 ISO). I noticed by comparing the pictures and found out high ISO with adequate exposure was pretty good, the noise level was not so obvious. any idea what's the rational behind this "shutter speed-high ISO" thinggy? why is noise being absorbed more easily when light intensity is high as compared to "normal light", but when you prolong your shutter speed it will take in the "normal" light instead of noise?

Hi GeckoZ, I found one post by one CS'er which explains the corelation between ISO-Shutter-Aperture

http://forums.clubsnap.org/showpost....28&postcount=3

[GeckoZ]

Originally Posted by dot1q Hi GeckoZ, I found one post by one CS'er which explains the corelation between ISO-Shutter-Aperture http://forums.clubsnap.org/showpost....28&postcount=3

thanks dot1q, but tt wasn't what i was asking for.

[ah.zeep]

Came across this site while trying to look for an answer to your question. (Actually, looking for an answer already out there in the web that will explain it so I didn't need to hazard a guess ) "Signal-to-noise" ratio may well be the reason, as described in that link.

Incidentally, I think that site has tonnes of other cool stuff to read about, too.

HTH.

[GeckoZ]

Originally Posted by ah.zeep Came across this site while trying to look for an answer to your question. (Actually, looking for an answer already out there in the web that will explain it so I didn't need to hazard a guess ) "Signal-to-noise" ratio may well be the reason, as described in that link. Incidentally, I think that site has tonnes of other cool stuff to read about, too. HTH.

Hi, thanks pal. The website got a lot of info. but the part on the ISO noise abit chim i couldn't understand it.

[theRBK]

To understand this, we have to look at how the imaging chip works:

Each imaging site, commonly called a pixel, absorbs the light hitting it and transform it into an electrical signal. The strength of this signal is then increased or amplified so that a better reading is taken. The readings are calculated from the strength of the signal at each pixel and an overall image is created.

At the base sensitivity level, commonly ISO 100, minimal amplification is carried out to the signal. To have greater sensitivity, >ISO 100, more amplification of the signal is carried out.

In the best case scenario, the signal that is read from the chip represents what is "seen" by the chip. But because some background electrical charge is ever present in the chip, some slight defects can be seen and this is what we call "noise". The reason we see more noise in high ISO is that the effect of noise is also amplified by the same amplification that is carried out to increase the sensitivity of the signal. But the more light is received by the chip, the greater is the signal produced before amplification, the less noise becomes a major factor as compared to the signal.

So basically, if you have more light (ie. if your image is well exposed) there is more information as compared to the background noise that the chip produces. If this were the case, all things being constant background noise is less visible as compared to the image that is produced. Also, if you notice, even within the same image, the darker areas have more noise than the lighter areas.

[Ghostrider117]

Like flim, high ISO no matter digital or flim, there will be grainy texture (or digital call noise). Usually high noise will come from dark areas. I use to shoot concert with Konica 3200, noise is bad when lots of shadow...so try to compose the picture so that you have lights on your pictures will reduce it. The noise is still there, just that with images, it distract the attention.

For DSLR, the processor is rather powerful...switch on the noise reduction to help lower noise...on my D80, its fairly well surpressed. But if wanna nick pick, still have noise. I am talking about ISO1600.

For my prosumer G6, even bumping the ISO to 400 would yield noise so bad that you wanna cry...

[GeckoZ]

Originally Posted by theRBK To understand this, we have to look at how the imaging chip works: Each imaging site, commonly called a pixel, absorbs the light hitting it and transform it into an electrical signal. The strength of this signal is then increased or amplified so that a better reading is taken. The readings are calculated from the strength of the signal at each pixel and an overall image is created. At the base sensitivity level, commonly ISO 100, minimal amplification is carried out to the signal. To have greater sensitivity, >ISO 100, more amplification of the signal is carried out. In the best case scenario, the signal that is read from the chip represents what is "seen" by the chip. But because some background electrical charge is ever present in the chip, some slight defects can be seen and this is what we call "noise". The reason we see more noise in high ISO is that the effect of noise is also amplified by the same amplification that is carried out to increase the sensitivity of the signal. But the more light is received by the chip, the greater is the signal produced before amplification, the less noise becomes a major factor as compared to the signal. So basically, if you have more light (ie. if your image is well exposed) there is more information as compared to the background noise that the chip produces. If this were the case, all things being constant background noise is less visible as compared to the image that is produced. Also, if you notice, even within the same image, the darker areas have more noise than the lighter areas.

Thanks pal, you've solved all my queries on ISO and noise.

[theRBK]

no prob

by the way, this leads to the school of thought which says that an effort should be made to expose the image to the right of the histogram even if the range of brightness levels is safely within the range that the sensor can capture...that is, in the histogram which shows brightness of the image, the graph would be near the right (bright) side...

this is to increase the signal that the sensor receives that is bright, where there would be less noise, as opposed to the darker areas where more noise would be present due to the lesser strength of the signal...of course, you have to make sure your highlights are not blown

this of course runs counter to what people normally say about digital photography, of exposing darker to preserve highlights as blown highlights are harder to retrieve than detail lost in shadow...this is true if you want to be really safe and want to make sure you have the shot like in high pressure situations with changing conditions and subjects...but on the other hand, if you end up having to boost brightness alot in your images, be prepared to have more noise in your images...not necessarily a bad thing, but you have to be aware of it and not complain that your camera is noisy...I have ISO 320 shots from my ancient E10 that have pretty good noise control...