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.