I really share your frustration with the color picker failing.
In my case, thanks to the digital ICE, function of my scanner, dust only becomes a problem when this function has to correct too large patches, still leaving “extreme” spots. I guess that using a camera-based method leaves you with more dust problems. After some “research”, I believe that my problem is based on some noise issue of my scanner sensor in the very low end of the spectrum (hence, only highlights [after conversion] are strongly affected). Or it could be some problem with how this is processed in Vuescan, producing grain aliasing. The result (after conversion) is either dotted/strip-like paterns of “too” white pixels in highlights - or elsewhere, pixels where at least one RGB channels randomly hits the maximum value.
No matter how this is produced, I’ve opted for a mix of modules to counter this effect. Of course, whether this works for others, depends on many factors.
- Denoise (profiled): Wavelets; Linear [default] diagram, strength 3, preserve shadows 0, bias correction 0; masking (I want to retain the grain in the rest of the picture): gray value 0 - 0 - 0 - 4.3 [applied on the negative, since the module comes before negadoctor]
This evens out most visible stripes in the (inverted) highlights which mess up the look of extreme highlights like reflections, lamps or the sun. - Diffuse or sharpen: Iterations 3; central radius 8px, radius span 3px; speeds: all at 100%; anisotropies: all at 0%; masking: gray value 0 - 0 - 0 - 1.6 [also applied on the negative before negadoctor]; blurring radius 4.0px
Using this module without the mask, the settings appear pretty random, but with the mask, it attempts to eliminate (dampen) only those final outliers which Denoise didn’t catch - and which tend to give you such extreme D Max values in Negadoctor. Of course, you could also use a similar module like Blurs, but there you don’t get such varied options for “playing around” with different diffusion parameters. Since I only wanted to apply this to the extreme highlights and quickly let it “fall off” below that, I had to test the settings on various images in order not to turn extreme highlights into washed out darker dots surrounded by unaffected lighter rings where the mask hat fizzled out (imagine a candle with a dark spot in the middle). Also, you have to constantly check the histogram and repeat applying the color picker in D Max.
As a result, the color picker in Negadoctor’s D Max now gives me much more normal values in all images - and thus, a more acceptable range in which to place the entire picture. At this point, I can more easily rely on the automated step of letting my Autohotkey script grab D Max from the selected “brightest” images of my 285 film rolls.
I guess you could still improve the individual settings (particularly in diffuse or sharpen), but I’m happy for now. It was only the “solving” of this problem that allowed me to realize that some analog photographs were simply underexposed and needed further corrections - as discussed in my other recent post (Fixing negative underexposure in Negadoctor) which you also reacted to.