Noise reduction for high ISO images

[asharpe]

Hi folks,

I just bought a Pentax K3, and the high ISO performance is much better than my previous camera (K20D). The K3 has no antialias filter, and most of the forums I have read suggest that the K3's auto noise reduction is too aggressive. So, I thought I would turn everything off and use PL to reduce the noise. I am shooting RAW, DNG format. But (in PL 18.02), the Filter->Digital Camera->Image Noise tool doesn't seem to work the way I would have thought, and, in fact, doesn't reduce the noise at all. I have tried the Adaptive Soften, which works better, but I would assume that the de-noise tool is the proper one for removing noise, right? How does this tool work? I tried it on an image at a medium ISO (1600 -- the camera goes to 51200), and while the Color Noise appear to remove some of the color noise, the Intensity Noise settings don't affect the noise much, if any. How do folks here use this tool? Is there a better tool for general de-noising of an image?

[photoken]

I thought I would turn everything off and use PL to reduce the noise. I am shooting RAW, DNG format.

You absolutely have to be using RawTherapee. It's free. It does an outstanding job on RAW images. It has several million adjustment options, so it will require some effort to learn, for sure.

PhotoLine's RAW image processing and adjustments are remarkably good for images that are good to begin with, and it does far better than its image-editing competitors. But for extreme images, specialized software is necessary.

For the specific case of reducing noise, others here will undoubtedly recommend their programs of choice that focus on noise reduction. It's up to you to test them and see what works best for your images.

[asharpe]

I am shooting RAW, DNG format.

You absolutely have to be using RawTherapee.

Well, that's fair. I had already downloaded it to my Mac, after using it a bit under Linux. I never used it a lot, but I suppose I was happy enough with PL's RAW handling. But the noise reduction in RawTherapee is quick and easy to use, so on the rare high ISO image, I'll use it. Normally, I'm at 100 ISO, on a tripod, doing macro. But sometimes, I'm handheld with a catadioptric (mirror) lens shooting birds, at high ISO (the mirror lens is an f8!).

[bkh]

I have tried the Adaptive Soften, which works better, but I would assume that the de-noise tool is the proper one for removing noise, right?

De-noise is very similar to Adaptive Soften, but allows to specify different strengths for colour and luminance noise, which is what you normally need for digital images which tend to have more colour noise.

Anyway, if you are processing RAWs with PL, it's best not to apply filters (which will force PL to convert your raw image into an ordinary RGB image) but adjustment layers – for some reason, "Image Noise" corresponds to the Denoise adjustment. Either add an adjustment layer, or turn on "Denoise" in the adjustment layer automatically created by PL when you open a raw image.

How does this tool work? I tried it on an image at a medium ISO (1600 -- the camera goes to 51200), and while the Color Noise appear to remove some of the color noise, the Intensity Noise settings don't affect the noise much, if any. How do folks here use this tool?

I normally use the Denoise adjustment as follows. (It's best to work at 100 % because at lower magnifications, the preview may be less precise.)

1) Turn on Colour and Intensity Noise, set "Intensity" and "Threshold" to 100 %, and "Intensity Noise Size" to 0.
2) Adjust "Colour Noise size" so that the colour noise disappears (or reduced to an acceptable level).
3) Set "Intensity Noise Size" so that the noise disappears (or reduced to an acceptable level).
4) Now lower "Threshold" until the noise re-appears and set it just a tad higher.
5) Fine-tune "Colour Noise Size" if necessary.
6) Sharpen as necessary (using Unsharp Masking, and adjusting its Threshold so that the noise doesn't reappear).

This may seem fairly complicated, but – as usual – PL doesn't offer you a "one size fits all" solution but many parameters to fiddle around with. Some raw developers make your life easier by choosing a suitable preset based upon the noise characteristics of your camera and ISO settings – PL doesn't.

Keep in mind that the noise you see at 100 % partially disappears when scaling down (or looking at the image from a normal viewing distance), so not removing it entirely may be a good choice. Also, the viewer is usually very good at seeing (or imagining) details in the noise which are lost if denoising is too strong.

Cheers

Burkhard.

[asharpe]

I have tried the Adaptive Soften, which works better, but I would assume that the de-noise tool is the proper one for removing noise, right?

Anyway, if you are processing RAWs with PL, it's best not to apply filters (which will force PL to convert your raw image into an ordinary RGB image) but adjustment layers – for some reason, "Image Noise" corresponds to the Denoise adjustment. Either add an adjustment layer, or turn on "Denoise" in the adjustment layer automatically created by PL when you open a raw image.

Aha! I had forgotten that the adjustment layer created for me with a RAW file has a denoise adjustment. It works fine, so that's what I'll use. I just couldn't get the Filter to work, and actually, because I don't want the layer converted, it looks like I'll never need it. Thanks!