Where does noise come from in my workflow?
 

I sometimes have problems with noisy images, and I can't quite get to the bottom of it. So, this is what I might do with a typical picture...where might noise be creeping in...where might I be better doing something else?

Shoot at ISO 100 wherever possible, try to have good light.
Copy RAW files into Bridge...sort through good and bad, and delete the bad.
Open an image in Adobe RAW...
Check for burnt out, or blocked up blacks on the histogram...adjust exposure, recovery if burnt out, slight increase in clarity. Tend to leave all other bits alone...
Open image in Photoshop.
May do a curves adjustment (on adjustment layer) if necessary, nothing fancy...S-curve mainly. May adjust saturation (again, on adjustment layer).
Usually add sharpening with unsharp mask, typically radius is around 1 max. Slide up until it looks ok, but not oversharp.
Crop to 10in x 8in x 300ppi.
Save as PSC and then as JPEG, quality 12.

Anyhting in there a problem, you think?
I wonder about cropping...if I crop to 10in x 8in 300ppi, am I adding pixels, or deleting some? If I crop with nothing in the size boxes I will get non-standard crop sizes, but will I then not be extrapolating pixels, or something?

I welcome all ideas to avoid noise in PP.

Thanks

Craig

2 things that will raise noise levels are sharpening and increasing contrast through curves or the normal slider. Have you thought about using a noise reduction plug-in for Photoshop ?

Hi,

I have tried noise reduction software, but much of it seems to leave the images looking mushy - might just be my poor handling of it, though. :)

Thanks.

Yes there is a learning curve with noise reduction. The thing is not to be too agressive in it's use and it is one of my first operations. In Photoshop CS5 I do it at the RAW conversion stage.

The sinlge most important thing for keeping noise down is to nail the exposure (which isn't always easy). A well exposed high ISO shot can look better than a low ISO shot that has had a lot of processing to pull it back for being underexposed. Looking in your gallery you seem to be using a 400D which should only start to need noise reduction on shots taken at ISO800 and above. I often use selective sharpening, only applying USM to the areas that need it (so don't sharpen backgrounds). Sharpening will make noise more noticable, so perhaps doing a little less sharpening will help. NR software can be very effective if used well, basically it smooths the image so counters the effect of sharpening - the trick is to balance sharpness and noise.

Thanks postcardcv...some good advice again. I asked this question on a couple of forums, and it is the exposure that is the common theme...I am working on that as first action point. :)

Thanks again.

Duncan always told me that the last thing to do was "sharpening". Not sure this will help, but worth giving it a go along with others' advice
Debbi

That's what I have been told in MOST cases. One or two suggest sharpening in RAW, though. I suppose I need to process an image a few different ways, noting where the noise creeps in to get the definitive answer.

Many Thanks.

The engineer in me can't help but look under the bonnet to understand how things work. While I agree exposure is a factor I have never found it to be a critical factor. There was a interesting series of articles on www.dpreview.com last year ( which sadly I can't locate) which looked at the differences in ISO settings. For example the difference between 100 ISO and 200 ISO could be that a different curve is applied as opposed to cranking up the sensor gain. It is really a question of knowing the camera's native ISO. It maybe better to operate at 200 ISO as there is no real noise benefit at a lower setting.

Just as a crude experiment I took some test shots to examine the effect of under exposure. They were shot under room lighting at a constant shutter speed but different f stops @ 200 ISO on a Canon 40D. Similar sensor spec to Craig's 400D. each shot was processed in Photoshop CS3 RAW with noise reduction turned off and default sharpening of 25. The top row was correctly exposed, the middle row was nearly 2 stops underexposed and the bottom row was 3 stops under exposed.

One thing I noticed when I adjusted the exposure slider was a marked increase in noise level. However, I also noted that the contrast of the grey scale wedge also increased dramatically when the exposure slider was increased.

I suppose Photoshop does this because it assumes that under exposure also means the available light will give low contrast.

After adjusting the exposure slider I reduced the contrast on the 2 under exposed shots to match the correctly exposed wedge. Attached is a composite of the 3 shots. If you compare the top row with the bottom row there is an increase in noise but not that dramatic considering it was 3 stops under exposed.

Noise reduction programs develop the best noise profile if the subject is purely noise and has no image data. A good subject would be an out of focus flat area of the scene. The closer the fit to the random noise patterns the smaller the impact on the wanted image.

Thnaks Rob. I wonder what the "native" iso for the 400d is?
An experiment is needed maybe?

An excellent response, and again, note3 being taken...I will nail this "problem",. iof indeed it is a problem and not a figment of my imagination. :)

Well, here's an image that people have said is noisy...


And the RAW is hosted here...

http://www.mediafire.com/file/9cp4ep...y/_MG_8811.CR2

If anyone wants to have a go and process this anyway they like, THEY CAN. Any help in my processing would be appreciated. :)

The file size of your jpeg might suggest high levels of noise but I don't know what compression setting has been selected. On the LCD screen at work I can see a bit of noise but hardly any on my aged CRT screen at home. Attached is my attempt which is 100Kb less than yours. This was saved with a setting of 10 in Photoshop.

The RAW appears to be over exposed if anything and lacking tonal range.

For this shot I used the auto option in CS5 ARC to get the levels in the right ball park and then tweaked as the change in black levels were over egged. Then applied some 30% noise reduction and sharpening at the RAW stage.

Does it appear cleaner to you ?

Thanks for posting the RAW file ... I'll take you through how I would process this with a series of screen shots to see if that helps you.

Attachment 7096
On opening the file in ACR the first thing is that as Rob says its got a very limited tonal range ... but its not over exposed - there are gaps at both ends of the histogram with no clipping

Attachment 7097
Switching to the details tab, as a default ACR applies some capture sharpening 25/1.0/25/0 which I always accept - RAW files always need a bit of sharpening and this is a very modest amount

It also applies default noise reduction of luminance 0, colour 25 - this I do NOT accept as the amount of noise reduction required varied with ISO. I have a number of ISO dependant default noise profiles which I have built for my camera (Canon 40D) and I have ACR (or Lightroom) apply them automatically depending on the detected ISO of the image. For more information of how to do this see <<<this thread>>>

Attachment 7098 200% zoom
Resetting the noise reduction to 0/0 for a minute and zooming in we can see that there is both some colour & luminance some noise present in this image ... which is to be expected shooting at ISO 400.

The sensor on your 400D is not dis-similar to my 40D so starting from my ISO 0400 preset of 15/5 I found it was still a little bit noisy so edge the setting up to 23/8. Noise reduction is always a balance between removing noise and softening details ... I tend to err on the side of leaving a bit of noise if necessary rather than sacrificing detail.

Attachment 7099 200% zoom
This would be my starting point before any exposure or black level adjustments etc. In the next post we'll look at how adjusting these setting affects the noise ... if at all

Ok now lets go back to the basic tab and adjust the exposure.

Holding down the ALT key while moving the exposure slide will mask the image and show us when clipping start to occur. In this image clipping begins at about +0.55 but I would accept a tad more clipping and kept moving the slider to +0.8. Doing the same with the black levels shows us that black clipping begins at about 30 but again I would accept a modicum of clipping and took the slider up to +45.

Attachment 7100
This gives us a nice contrasty image with the histogram filling the scale ... but what has happen to the noise levels?

Attachment 7101 200% zoom
OMG ... so that's where the noise comes from :confused:

Attachment 7102
Looking at whether is the increase in exposure or increase in blacks we can see by comparing to the un adjusted image in the middle, increasing the backs tends to emphasise luminance noise and increasing the exposure increases colour noise.

Attachment 7103
If we then apply a modest smart sharpen on Photoshop say 150% and 0.5 pixel radius it gets even worse :( Looking at your image it looks at though you have been considerably more aggressive with your sharpening - I'm guessing something like 200% & 2/2.5 pixel radius, possibility to try to compensate for the lack of depth of field. This will emphasise any noise HUGELY!!

... continued in next post

Whenever I push either the exposure or blacks levels significantly I always revisit the noise reduction setting before opening in Photoshop.

Attachment 7104
In this case increasing the luminance setting to 65 and the colour setting to 25 gives reasonable results I think.

Finally opening the image in PS, cropping and applying a modest sharpen again is about as good as its going to get - IMHO

Hope that helps

That is a fantastic piece of work, Clive...thanks. I have had loads of good advice, here and in other places, since I asked this question, but this write-up is fab!

Many thanks. :)