Thursday, December 11, 2014

HiRaLoAm effect with PhotoFlow

The so-called "High Radius Low Amount" sharpening method (HiRaLoAm, originally introduced by Dan Margulis) consists  to apply the unsharp mask filter with a large radius (let's say more than 10px) and a low amount (typically below 40%). The method is more a local contrast enhancement technique than a sharpening one: the halos that are created by the large radius add "volume" to the image and give an impression of increased local contrast.

While this is a quick and "dirty" local contrast enhancement technique (which might produce visible halos in the final image), it can be quite instructive to see how this can be achieved in PhotoFlow by simply using the gaussian blur filter and the appropriate layer blending modes, and can be an easy way to give your image some  more "pop".

Through this short tutorial you will also see how to create and high-pass filter, as it is one of the necessary steps of the HiRaLoAm technique I'm showing here.

First of all, open an existing image and add a group layer at the top of the layer stack (I've called the group layer "hiraloam").



Then, add a gaussian blur filter inside the "hiraloam" group and set the blending mode of the layer to "grain extract". This produces and high-pass version of the original image. As a starting point, set the radius to something between 10px and 20px. You will have the possibility to tweak it afterwards if needed.



We are now one step away from enhancing the local contrast... all you need to do is to set the blending mode of the group layer to "Overlay". Et voila', your image immediately gets some "pop"! Or maybe too much "pop"... you most likely need to reduce the effect by lowering the opacity of the group layer until the result doesn't look artificial.



Here is my final result for the grasshopper picture, using a blur radius of 20px and an opacity of 50%. Move the mouse over the image to see the original.


Simple, isn't it? You can now save the "hiraloam" group as a PhotoFlow preset, and load it back to quickly apply this technique if your image looks a bit "too flat".

2 comments:

  1. Hi Dear carmelo,
    Thanks a lot for this expert method. I use it now with Photoflow for my texture.
    Patrick Depoix

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    Replies
    1. You are welcome! Have you ever tried the "enfuse" program? It allows to increase the local contrast in a much more sophisticated way that the method I've proposed, with no visible halos.

      I've plans to include it as part of the raw processing ("enfusing" different exposures from the same raw file), but you can already use it from the command line... it's usually part of the "Hugin" package

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