Noise Reduction in the Work Flow

[Ken Fournelle]

Where do people like to use a noise reduction plug-in during he work flow? On the duplicate background layer at the beginning? After global corrections to color, contrast and levels? The end of the process?

Ken

[Andrew B.]

I usually run it first. Otherwise the noise interferes with how I perceive the image as I make other adjustments. But I think there were some cases where the noise started to show up again after I made other adjustments. And in these cases, I really needed to do other adjustments first, do see the extent of the noise. But usually, first works best for me.

[Gary Richardson]

I usually apply noise reduction close to or at the end of a job. As several photoshop processes introduce noise to your image, you would be duplicating your effort to do it earlier.

[saby]

Hi Ken!

There are several kind of noises. These can apears in the color (ex.: negative slide scan), in the lightness and both. When i recognise the NOISE first thing what i do locate it where does it apear. To reduce the color noise change picture Lab mode set channels to work only a and b and use the dust and scratches filter, this way reduce the noise but lighness kept untouched.This correction should do at the begining of the work. Ligthness noise is more difficult to do. When I have to reduce noise from the lighness I always make a mask for the edges, there are many ways to do - U can read about in Tutorials -, because reducing noise makes less sharpness so whit the mask i can keep the edges untouched. This correction should do after every mode changing(Lab->RGB ->CMYK) use different values of the filters depends on amount of noise apearing in the active channel. To answer simply: I think best to get noise loss as soon as possible.

Saby

[byRo]

There are several kind of noises......

Here's a theory:
(sometimes I'm better at theories than practice)

There are so many sources and types of noise than can affect the photo. Just think of what this poor image may have suffered along the way...
- Noise in the original scene;
- Noise in the camara / film;
- Noise in the processing / negative;
- Noise in the printing;
- Noise in the storage of the print;
- Noise in the scanning
..... and probably a lot more (jpg for exmple)

A logical answer would seem to be to work backwards, something like:
- Reduce jpg / scanning noise;
- Take out coffee stains and torn / bent / missing parts;
- Fix levels and colors to get back to the original print, then maybe....;
- Take out printing / film / original noise etc..

OK, I did say it was just a theory!

[john_opitz]

Start with your noise/artifact reduction as soon as possible. Before it creates problems when further corrections are going to be done. Example: Channel blending. You don't want to blend a noisy/artifacted channel into another. Unless that's what you want. Lab blurring with the "a", "b" channels , can take a heavier blurring than with a single RGB channel. If worried about conversions (rounding errors). *Make a duplicate of your RGB file* and *convert the duplicate to LAB*. *Do your blurring of the "a", "b"*, *Select all (composite channel)*, *copy/cut*, *paste into a new (empty) layer on your RGB file*, *fade that to color mode*. Making an action of this helps, time-wise. But you can go RGB>LAB>RGB. Depends on how you feel about rounding errors.

[saby]

...But you can go RGB>LAB>RGB. Depends on how you feel about rounding errors.

Hi John!

rounding error means lose data at color mode changing?

saby

[Flora]

Hi everybody,

Ken

It's a habit for me to always check the Channels before doing anything else ... If most of the noise is in one Channel, you could try reducing it by blurring or actually running your noise reduction plug-in on the single Channel ....

My second step is fixing exposure, tone and contrast .... and, particularly with darkish/underexposed pictures, the noise tends to 'show up' after lightening up the image ... In that case, that's when I run my noise reduction plug-in ... so, like John, as soon as possible ...

Just wrote a Tutorial on an alternative way of using noise reduction software ... in my case Neat Image ....

[john_opitz]

Hello saby,

<<rounding error means lose data at color mode changing?>>


Yes. If you want to look at it that way. But how I feel about all of the rounding errors stuff....... Is it noticeable (loss) on screen and more inportant, shows on your final output? Mathematically.......Well it would be. How I feel about it?..........Is taking the medication better for you than the side-effects will be? This is how I take to it. Even doing curves/levels in RGB does some damage to a file. I don't look at it this way, though. If correcting an image that is better than before with whatever technique is considered damaging to the file, so be it. Their are some techniques that are less damaging than others. As long as it is not visible on output. As for the life of the file. Well....Repeated edits will damage the file no matter what color space your in. The knowledge is knowing how far to go. As what flora says (see her post). Btw. Helloooo. Flora. Its great to work with a file that you don't have to denoise/artifact-remove. But depending how the image was handled (shot at high ISO from a camera, how far was the jpeg compressed in camera) this is not the case. Cameras (digital) are getting better and better in this dept. And in a way its unfair for the engineers that make em'. Photographers want to see very little to no noise in images shot at high ISO speeds. They have taken care of the noise problems compared to earlier D-cams for the lower ISO speeds. Photographers forget when using a high speed film they were stuck with the noise.........or I should say.....grain. Now we have complete control on the editing of our files (if we want). In all, I don't worry about the losses, compared to the advantages.


John