Check this out

[devilgas]

Re: Check this out

No, no, no you are missing the point of my little game

par for the course then

was the image run through LR3?

i'd be interested in seeing what the straight-from-cam image, with no additional processing or downsizing, looks like. i know what my cameras produce at high iso and what they can look like after pp.

[Ian]

Re: Check this out

It is difficult to evaluate on the web - the downsizing tends to have the effect of cleaning some of the noise. I would guess that ian's example is frm an m4/3rds camera - EP2 or E-PL1.

That's the easy part - but what about the ISO speed?

Ian

[Stephen]

Re: Check this out

Sorry Stephen - that's the wrong way round

If the camera was set to ISO 6400 and you increased the exposure in LR by half an EV, your equivalent ISO is reduced to ISO 4800.

Ian

Well if you say so Ian, but I can never understand it myself
My thinking is this. If I shoot in camera at iso 100 and apply exposure compensation of +1 stop/EV ie overexposing, then its the same as increasing the iso to 200 and keeping the same setting. So if I do this in LR, it seems to me I'm effectively doing the same. I can understand though that it may not be exactly the same as increasing the gain on the sensor as you do when turning the iso up

[devilgas]

Re: Check this out

Sorry Stephen - that's the wrong way round

If the camera was set to ISO 6400 and you increased the exposure in LR by half an EV, your equivalent ISO is reduced to ISO 4800.

Ian

eh?

if you increase exposure in software, you're amplifying the luminance of the pixels. if you increase the iso on the camera then you're amplifying the signal from the photosites of the sensor.

given the aperture and shutter are fixed at the time of taking the photo, increasing the exposure in pp is the direct equivalent of increasing the iso surely?

[Stephen]

Re: Check this out

That's the easy part - but what about the ISO speed?

Ian

Well I've had shots with the E-P1 taken at iso1600 and 3200 that were perfectly acceptable and possibly on a par with this example. If it was taken with a smaller sensor camera than that and at a similar iso then I'd be even more impressed

[Ian]

Re: Check this out

Sorry Stephen - that's the wrong way round

If the camera was set to ISO 6400 and you increased the exposure in LR by half an EV, your equivalent ISO is reduced to ISO 4800.

Ian

Actually, that's not right! Sorry

The brightness is increased to an equivalent of about ISO 9600 (and noise increases when you brighten in post processing of course), but the exposure (aperture and shutter speed) remain un-changed of course, so they are still at ISO 6400.

My thinking that the ISO had been reduced is of course from the perspective of managing settings at the time the image was shot - to get that brightness level you would need to reduced ISO by half an EV in order to alter the shutter and/or aperture appropriately.

Ian

[Stephen]

Re: Check this out

par for the course then

was the image run through LR3?

i'd be interested in seeing what the straight-from-cam image, with no additional processing or downsizing, looks like. i know what my cameras produce at high iso and what they can look like after pp.

It was only corrected for WB and given +0.5 exposure increase in LR3.

Give me a few mins and I'll PM you a link to download the full raw file

[Ian]

Re: Check this out

eh?

if you increase exposure in software, you're amplifying the luminance of the pixels. if you increase the iso on the camera then you're amplifying the signal from the photosites of the sensor.

given the aperture and shutter are fixed at the time of taking the photo, increasing the exposure in pp is the direct equivalent of increasing the iso surely?

Yes - sorry! - I corrected myself earlier in a follow-up post. It's slightly confusing!

Ian

[devilgas]

Re: Check this out

It was only corrected for WB and given +0.5 exposure increase in LR3.

Give me a few mins and I'll PM you a link to download the full raw file

cool. wasn't sure if you'd applied any of the LR3 noise reduction stuff which is supposed to be pretty impressive. will download tonight if that's ok?

merci.

[Stephen]

Re: Check this out

Actually, that's not right! Sorry

The brightness is increased to an equivalent of about ISO 9600 (and noise increases when you brighten in post processing of course), but the exposure (aperture and shutter speed) remain un-changed of course, so they are still at ISO 6400.

My thinking that the ISO had been reduced is of course from the perspective of managing settings at the time the image was shot - to get that brightness level you would need to reduced ISO by half an EV in order to alter the shutter and/or aperture appropriately.

Ian

Phew, thank the Lord, you were about to debunk a basic principle I've held since.......................well, since I don't know when

[Ian]

Re: Check this out

The point that was previously made about the effect of down-sizing is well worth pointing out. Noise is at the pixel level (although clumping can involve up to dozens of pixels) and when reducing a 22MP image to under half a megapixels here on the Web, you're squeezing the image information into just two percent of the pixels you started with. A lot of noise visible at 100% in the original file will simply vanish.

Ian

[Bear]

Re: Check this out

I have, sometimes, seen downsizing touted as an effective noise reduction technique and of course, as Ian says, it works. Noise is only information after all and if you remove a lot of the information, you remove a lot of the noise. In truth, removing noise from an image is not difficult. The hard part is removing the noise whilst retaining the important detail. This is tough but there are amny tools out there that do a pretty effective job.

[Bear]

Re: Check this out

Another effective technique is to convert to B&W. Although this doesn't really remove any of the noise it does mask it and reduce the negative effects on the image somewhat. Colour noise is a lot more intrusive than other forms of noise. By converting to B&W you remove the destructive effect of colour noise and leave a less objectionable, grain like effect.

[Ian]

Re: Check this out

I have, sometimes, seen downsizing touted as an effective noise reduction technique and of course, as Ian says, it works. Noise is only information after all and if you remove a lot of the information, you remove a lot of the noise. In truth, removing noise from an image is not difficult. The hard part is removing the noise whilst retaining the important detail. This is tough but there are amny tools out there that do a pretty effective job.

Of course if you are down-sizing for the Web anyway, it's a win/win situation.

Printing can also reduce the obtrusivness of noise considerably.

Noise is most visible on-screen and particularly when viewing on an LCD monitor. Old CRT monitors mask a lot of the effect of noise - indeed they are on a par with printed results in terms of noise rendition.

In many ways, noise is a bit of a red herring. It's not the noise itself that is often the problem, but its effect on obliterating detail (which you rightly mentioned).

Chroma noise can be nasty and difficult to eliminate unless you eliminate the colour of course - which you also mentioned!

Ian

[Ian]

Re: Check this out

Another effective technique is to convert to B&W. Although this doesn't really remove any of the noise it does mask it and reduce the negative effects on the image somewhat. Colour noise is a lot more intrusive than other forms of noise. By converting to B&W you remove the destructive effect of colour noise and leave a less objectionable, grain like effect.

Reducing saturation is also a good way of managing chroma (colour) noise.

When post processing RAW, reducing the brightness, especially by increasing the dark end of the histogram, is a very handy tool, also. This is why exposing 'to the right' of the histogram is recommended. If your image is on the brighter side, reducing that brightness in post processing will suppress noise - you just have to be careful with blowing highlights.

Ian