Am Samstag, 17. Februar 2018, 15:57:04 CET schrieb Anton Aylward: > This question is in two parts. > > Context: my camera has the ability, while working in JPG mode, to take a > B&W photograph except for one colour. I can select red, blue, green, > yellow. Check your own DSLR, you may have something similar. > > Imagine taking a oblique view of a parking lot, the cars all parked nose-in > and the sunlight reflecting off their red rear reflectors. Capture that; > the cars in B&W (unless there is one that's a bright red sports!) but just > the red reflectors lit up. > > Sidebar: I've just tried this with some pictures of evergreen in the snow, > but I don't think much of the result. > > My first question is this: I have older photographs in full colour taken > with other cameras, some with film that has been scanned. Can I get > Darktable to do this transform? The answer must be 'yes', but I get > confused along the way. > > I see in the docco that there are a quote a number of different RGB settings > that can make up B&W for various different types of B&W film. I can > imagine picking one or another or another and then sliding the RED up in > colour adjustment. > > But that doesn't give me what I want. How do I get yellow? > What if I take a picture of one of downtown buildings that has gold plated > thermally efficient windows and just want the gold to stand out? > > I can imagine more grief with masking! > > > > The second question is a good but more complicated and I realise it probably > does involve masking. > > There are a number of structures that are like maypoles, they are colourful, > multicoloured. So I can't simply go B&W and then pull back colours. I can > see this being done in GIMP with a couple of layers; pull out the maypole, > make the rest of the image B&W in anther lay, overlay. But is there a > straight forward way t do this in Darktable without combining overlays, a > sort of HDR for a single feature? > > All of this without getting too complex, perhaps make it script-able.
I'd use the monochrome module to make the whole image b&w. Then use parametric masks to take out some parts of the image, for example the red tail lights. It might be necessary to combine parametric masks with drawn ones. Something related: https://www.darktable.org/2012/07/some-enhancements-to-conditional-blending/ Tobias
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