Wednesday, 27 July 2016

Noisy pictures and other synaesthesias

I have an important problem about the noise in my pictures. I've tried to find the cause of it several times before. In this post I try to bring a little of knowledge light to this problem.

One of my worst fears about the noise in my pictures is that it could be caused by the cleaning of the sensor. I wrote a post about the cleaning of a camera's sensor some years before. there, I talked about the risks of the process for amateur hands and finally I had problems with the totally elimination of the dust.

I've been reviewing old pictures of skies taken by me when I bought the camera, before of the first sensor's cleaning. I haven't found exactly equivalent pics (with the same parameters: the same gear, the same focal length, the same f-number, etc.), but I think you can note from a qualitative point of view that the noise has not increased with the sensor's cleaning.

Note that he noise depends of several factors, like the external temperature. In this post we don't pretend to make an exhaustive analysis of the noise and the influence of the environment variables. The aim is to find the main noise's source and the way to reduce that noise in every situation.

The second hypothesis is that noise would be generated by the post-processing. I use RawTherapee as post-processing software. All my pictures are processed by this software, with automatic profiles that could include noise in all my pics in a systematic way.

The previous images seem indicate that the problem is in the post-processing. The no processed image has a little amount of noise (because of the ISO speed), but much lower than the processed image.

In the series below you can view the influence of the post-processing in the noise (scale 100%).

Watching the previous images, I think the focus mask (with a reasonable values) is not the main problem. A combination of over-saturation and, mainly an aggressive treatment of the tonal curve seem be the most important causes of the noise in my pictures.

The conclusion in this point is that you can't to abuse of the post-processing. But, could we forced it a little?

The answer is in the blur filters included in RawTherapee.

RawTherapee has several options for focus and blur masks. With the proper combination of parameters, is possible to have sharpness and blur the noise at the same time. This is my new configuration:

  • Focus mask: Active
    • Radius: 1.50
    • Quantity: 120
  • Increase Noise Reduction: Active
    • Limit: 50
  • Noise Reduction: Active
    • Method: RGB
    • Luminance: 0
    • Luminance detail: 50
    • Master chrominance: 15
    • Red-green chrominance: 0
    • Blue-yellow chrominance: 0
    • Gamma: 1.70
    • Quality: High
    • Median: Active
    • Median method: RGB
    • Median type: 3x3
    • Median interactions: 1

It has not been well tested yet, but I hope it will make disappear the noise of my future captures.

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