Canon High ISO noise reduction setting

[arad85]

I've seen various posts saying have this set to on, and others saying have it set to off. I've also tried to find a technical description of what this does on t'internet, but all I can come up with is "reduces noise in pictures taken at high ISO settings" or words to that effect.

Does anyone know what it actually does?

[jgs001]

Not exactly, but it's like running a noise reduction process in PS... it'll reduce the image sharpness a bit (probably using some form of smoothing algorithm). I leave it off.

[arad85]

Thanks John,

Figured I'd get a post from you on this

There are two modes I'm thinking of using this for. The first is on a tracked mount - then obviously, you'd be better off with it off... The second is where you take a number of 20 or so second frames to do some widefield movies. I'm thinking (as you're not stacking anything there) you'd probably be better with it on.

But what is defined as "high ISO" 400, 800, 1600

[jgs001]

... I'm really not sure on the movie... to be honest, unless you're wanting to do some form of real time sort of time lapse thingy... then you'd be better off with ICNR rather than high ISO... Yes it takes another 20 seconds or so, but it'll do a better job of removing the noise.

As for what Canon consider high, I've no clue, and the manual is of no help whatsoever... I tend to operate on the basis that 800+ is high... I frequently use 400 on daytime shots if I'm wanting to really push the shutter speed or am working at handheld macro in bright light, and I reckon if I'm using it frequently, it's not High (not sure my logic holds water but hey... ). Also Canon set 400 as the bottom setting in Auto ISO mode I believe.

[NickH]

I think S@N hit the nail on the head. Whilst integrated noise reduction systems are really getting quite good, nothing quite beats a good calibration set of proper darks etc..

[dph1nm]

Doesn't the "High ISO noise reduction" only affter jpegs, not RAW?

There is some stuff here about the 40D:

Canon EOS 40D High ISO Noise Reduction Test The World According to Roland

NigelM

[jgs001]

It might do Nigel, but even when shooting only raw, this option slows down write speeds.

[themos]

I think it only does some chrominance noise reduction, the kind you can do with DPP anyway. turn it off!

[arad85]

Thanks all. The link above is good and one of the comments points to this:

http://www.usa.canon.com/uploadedimages/FCK/Image/2007/MARK%20III%20Suggested%20Settings%20121207/EOS1D_1DsMark_IIIoptimizingAFsettings_Final.pdf

which, on it's last page, says what the function actually does on the EOS-1DIII. It would seem sensible that this would apply to the 450d function as well (although they may have tweaked it).

The reason I'm asking is that I did some time lapse stuff on a fixed tripod and it is quite noisy. I can't stack the images as I want to "make a movie" with the resulting output. I also wasn't too bothered by ultimate quality as I would be shrinking the output to display on a TV, so I shot in .jpg format. Next time I do it, I'll do two sequences with the high ISO on and off for comparison.

I'd agree with off for general use though

[ngc2403]

I think the bigger problem is High ISO, I have been reading and found that Higher ISO adds only noise to and image, and degrades the SNR of all images.

So i have now been shotting all images day and night on the lowest ISO possible, I know that this means level adjustment later but where this is a drag for daytime photos it is not a problem for DSO because you need to do image processing anyway

ally

[jgs001]

Which is fine to a point Ally, and I've seen some great DSO images at ISO200... but lets use day as an example... you're handholding a non stabillised 400mm lens, the light conditions do not allow you to get a shutter speed of 1/400 (the accepted shutter speed for hand holding a 400mm non stabilised lens, some can use lower, some need higher but...) however, ISO100, only allows you to use a shutter speed of 1/50... are you not going to increase the ISO to get the shot ? If you don't and you stretch the shot to get the signal out of it, how much noise is that stretching going to introduce ? My experience is that the ISO noise is easier to deal with, and actually less intrusive in the shot that the noise caused by stretching out an underexposed image. If you get the daytime exposure right, and you're not pixel peeping, then even with the 450d at ISO1600 (maxed out), you get very acceptable results.

For night time use, whilst good results at low ISO's are possible and you can stretch the data out, I've only ever had even more noise pop out with the low ISO frames of the same length.. I'd need to double the exposure time for each down stop in ISO to get the equivalent exposure and not have to stretch so hard.

[ngc2403]

I know wat ur saying about the day time i don't under expose day time shots, and so i use lowest possible ISO that i can, while still getting a proper shutter speed..

Stretching an Image is a noise free process.

no noise is added to the image as both noise and signal are scaled at the same rate.

A single shot at a set exposure properly corrected with bais, darks, etc has the same dynamic range as a shot taken with a higher ISO and less Noise caused by the ISO/ADC/gain wat ever u want to call it.

this works best for long exposures of 5mins or more but my rule of thumb is lower is better

[arad85]

An interesting point from the Canon tech paper is that although it is described as High ISO, if it is switched on, it appears to work at whatever ISO you are taking the photo.