This is not as strong as the darktable version. This is too strong! If I do the same using Pat’s luminosity masks in GIMP, I get: Here we moved both the upper triangles to the center. We now move the top right triangle to the extreme left: In darktable, we simply do the opposite of what we did for the L mask. To create the D mask, Pat selected the whole image, and subtracted the L channel from it. How does the image look with the same curve as before? By sliding the upper left triangle all the way to right, I told it to fully select the brightest pixels, not select the darkest pixels, and do a linear interpolation for all the intermediate pixels (so a 50% bright pixel is “half” selected).Īnother way of looking at it: Apply the module to all the pixels, but apply an opacity on each pixel depending on its luminosity. What did I do here? To fully understand it, you should read the parametric masks page in the darktable manual. Now comes the important part: In the Input sliders, select the top left triangle and move it all the way to the right: Go to the Tone Curve module, set blend to parametric mask. This means any operation we perform on the image will be applied more on the brighter pixels. Using Pat’s technique, let’s look at the L mask in GIMP:īrighter areas mean they are “more” selected. Let’s use this as a “control” for the effect of luminosity masks. In that sense, some refer to these masks as self-feathering. There are no sharp transitions like what I have in my screenshots above. When you now brighten the image, the effect of the brightening is greatest on the brightest pixels, and least on the darkest pixels. So the L layer in Pat’s article fully selects completely bright pixels, and only partially selects pixels that are half as bright, and doesn’t select pixels that are not bright at all. What luminosity masks do is let you select regions in your image in proportion to their brightness. We’d really like is a way to select based on the actual contents of the image. You can feather it even more if you wish, but however much you feather it, the transition is determined too heavily by your choice of selection (a rectangle in this case). Feathering simply makes the transition less sharp:īetter, but still too sharp a transition. The quick solution is to blur the mask (feathering in GIMP). First, I strongly suggest you read Pat David’s post and thoroughly understand what’s going on.Ī quick and simplistic explanation follows: Normally, if we make a selection and, say, adjust the brightness dramatically in that selection, we get a sharp (and ugly) transition near the edge of the selection: I thought I’d post a quick tutorial on luminosity masks using parametric masks. Can darktable do something similar? Yes – they’re a special case of parametric masks. I recently read his post on luminosity masks and was fairly impressed. Pat David has a great blog on photoediting in GIMP.