In 2009 I wrote a small article here about a new class of image enhancement algorithms. Such algorithms made pictures look sharper by added local contrast and brought out details in both shadows and highlights. And they did this without adding halos around high-contrast edges such as the transition between foreground and sky. The article focused on a research paper by Farbman, Fattal, Lischinski and Szeliski (FFLS, 2008).
The brand new Lightroom 4 (and the associated versions of Adobe Camera Raw 6.7) has now incorporated similar technology that is based on a newer research paper entitled “Local Laplacian Filters: Edge-aware Image Processing with a Laplacian Pyramid” by Paris, Hasinoff and Kautz (PHK, 2011).
The implications of this new Lightroom feature for photographers are significant enough that I will gradually add more details here as I upgrade to Lightroom 4 (possible since March 5th) and get hands-on experience with it.
What’s so important about this technology?
On superficial examination, the two mentioned research papers (and there are many more where that came from) seem similar enough. They are both trying to give users the ability to make details in images more striking (local contrast enhancement) without creating undesirable artifacts such as halos.
The weird thing about this research is that they don’t distinguish between minor image tweaking (e.g. typical raw converters sharpen images to some default degree) and image modifications like HDR which also sharpen the image but can lead to unnatural results if overused. This is probably because there is no sharp boundary between enhancing a little and going overboard with your the settings.
Thus many of the example images in the research papers look like what we photographers would consider HDR photography: in HDR photography, you want to show a broad range of lightings without making the local contrast look flat, and without making the overall picture look artificial. Probably the authors would answer that HDR is an application area where this kind of algorithm is needed – but they can also be used for “normal” images shot with a single exposure in a Normal Dynamic Range situation.
Something similar applies to the Lighting module in DxO Lab’s “DxO Optics Plus”. It probably uses a similar type of approach to boost local contrast. I tend to consider it an HDR-like technique.
A claimed key benefit PHK as chosen by Adobe is that the algorithm is simpler and thus takes less processing time. In fact, the paper’s introduction starts off by saying that the widely known (in the right circles) Laplacian Pyramid technology was underrated, leading previous researchers (including FFLS) to develop more complex algorithms to compensate for its shortcomings.
It is worth noting that the first author in PHK works for Adobe. But these are scientifically reviewed papers published in respectable conferences – meaning the authors have to be very rigorous about their claims, when these hold and what evidence and even counter-evidence there is for these claims.
Where do I find this in Lightroom 4?
Now shipping in Lightroom 4 (and Photoshop CS6 Camera Raw) – the tools for adjusting shadows, highlights, and clarity are based on a fast version of the local Laplacian filters we introduced at SIGGRAPH 2011