Denoise – sharpening improvments
For several months (September / october 2024), I’ve been challenging myself to improve noise processing overall, based on the basic principle that ‘the human brain still has unsuspected capabilities compared to artificial intelligence’, but maybe this challenge is too ambitious… We’ll see what your opinion is ? What is generally certain is that my solution is more complex to implement.
Observing the current operation leads me to the following observations:
- ‘Capture sharpening’ is probably the best tool for sharpening images, but it suffers from two major flaws:
a) if the image is too noisy, the default system doesn’t work;
b) it can’t be used on non-raw images.
The noise reduction system, whether in Detail tabs or in Selective Editing, is subject to the principles of RT’s four pipelines, and therefore what we see on screen (zoom) doesn’t match the final rendering well (this is an understatement and affects all processes).
Noise reduction inevitably leads to a reduction in sharpness. Regardless of the tool, with or without masks, certain details are “weakened”…
I proceeded in several stages :
-
to overcome ‘a)’, I set up in ‘Capture sharpening’ (Raw tab) a ‘Presharpening denoise’ which applies gradually by successive iterations a light ‘3x3 soft’ to a fairly strong ‘5x5 strong’ median denoising filter before Capture Sharpening. This helps clarify the contrast mask and allows Contrast Threshold to work, and thus Capture Sharpening to work properly. This also helps to reduce noise in the output image. Be careful not to use values that are too high so as not to degrade the image.
-
‘Show contrast mask’ is directly accessible from the main menu.
-
For level ‘b)’, I implemented in Selective Editing ‘Capture Deconvolution’, which is an adaptation of Capture Sharpening in Raw tab (almost the same), to Selective Editing and allows you to use this algorithm alone or after denoising. Capture Sharpening’s capabilities allow for finer sharpening control by allowing you to soften the sharpness in the corners, thus enhancing the main subject’s focus. Unfortunately the system is still dependent on the 4 pipelines and the zoom problem. Consequently, the results in the TIF/JPG outputs correspond to those of ‘fit to screen’.
-
To solve part of the problem I added in ‘Capture sharpening’ (Raw tab) a ‘Postsharpening denoise luminance’ which allows you in raw mode (with wavelets), to do an initial luminance denoising after Capture Sharpening taking into account the mask information. ‘Presharpening denoise’ must be greater than zero. Be careful not to use values that are too high, you can fine-tune the noise reduction later. Obviously this system which is in Raw mode is not sensitive to the effect of the 4 pipelines.
-
The ‘Selective editing denoise’ module has been extensively revised; it allows you to differentiate Denoise action based on image details and your wishes to process the background. The resulting action is the combination of the Denoise of the image and that of the mask created by ‘Contrast threshold’. On very noisy images you can reduce the mask noise. You can also differentiate the action with the curve ‘Equalizer denoise mask’. The ratio flat-structure areas allows you to correct the action between the two. But unfortunately the system is still dependent on the 4 pipelines and the zoom problem.
In summary for Denoise and Sharpening:
- Capture Sharpening (Raw tab) allows you to improve its performance with noisy images in many cases and to perform noise preprocessing.
- Denoise (Selective Editing) is more efficient, particularly thanks to the ‘contrast threshold’.
- Sharpening (Selective Editing) has added a module similar to ‘Capture Sharpening’ (Raw tab), allowing you to process non-raw images and also to enhance sharpness after a possible denoise.
Blur the background and isolate the foreground
In Selective Editing, except ‘Global’ mode, you can now detach the foreground to highlight it and soften the background.
This is a similar approach to the one used in this example to differentiate the denoising action between uniform areas and areas with texture or detail - Recovery Based On Luminance Mask
Denoise in Selective Editing
You can use the following tools to blur the image:
-
Gaussian blur – Noise – Grain.
-
Median.
-
Guided Filter….
And of course all tools ‘Denoise’ (wavelets, etc.).
Probably, given my poor English and my limited knowledge of C++ code, the code, labels and tooltips are questionable, but I am open to any modifications.
Executables - captur-noise
Bin
Jacques
