@ Bart
Thank you Bart. Thank you very much.
I already new some of the issues you are pointing to and now, that I have been opening the image in raw in the final version, I realized that the problem may be an incorrect exposure of the photograph that being the cause of the degradation.
On the other hand, the histogram looks fine.
Hi António,
I've had a look at the Raw file data with the excellent
RawDigger tool, and that shows that the exposure is excellent. The exposure is very close to clipping in the highlights, so any more exposure would have started losing highlight information.
That leaves the natural noise of light (photon shot noise), and the noise characteristics of the sensor and its read out electronics (read-noise + pattern noise). There is not much you can do about that, except use as low an ISO setting as possible (if exposure time permits). That is also important because it is a file from a camera with a 12-bit/channel ADC, and that means that even a well exposed image like this one, will have a lower S/N ratio than a more recent camera with 14-b/ch ADCs.
That leaves Raw conversion and software noise reduction as possible remedies. Since you wanted to emphasize the cloud structures in the highlights, it is important to use a Raw conversion that does not compress the highlights too much because subsequent contrast enhancement will also boost micro-contrast and noise. Lightroom and Photoshop ACR with process version 2012 will use a lot of highlight compression by default, so you would need to use a minus Highlight correction to reduce that behavior.
Personally I prefer the conversions from Phase One's CaptureOne software, with a Linear Response Curve setting, not a Film curve that also uses highlight compression. But even with that, your file does produce some challenges for an artifact free end-product.
Most probably the noise is introduced after the manipulations I introduced to the original file until I get what I want.
Yes, I also needed to separately find a solution for this file. I had to create a mask to apply the noise reduction only to the sky, without softening the rock/ground structures. For that, Photoshop or an other Layer based editor is indispensable. DeNoise 5 also allows to target the sensor's pattern noise that is present in the clouds, which will result in a smooth sky that will then benefit a lot from applying Topaz Labs Clarity to the entire image.
This is something I really have to be careful about. As you said yourself the noise is more or less important according to the size of the final printed image, if I have understood correctly.
Correct, at a small enough size the noise will not be easy to see, but when enlarged, it requires extra work to visually improve the output.
Cheers,
Bart