Lightroom 4′s PV2012 image enhancement algorithm

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.

Alternative algorithms

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

Source: https://plus.google.com/116168853211931020305/posts/id3W5HZcdFN

Should we care?

6 thoughts on “Lightroom 4′s PV2012 image enhancement algorithm

  1. Agustin Castro

    In HDR-imagges, the number of tonal values can be enlarged from 256 (typical of 8-bit images) up to around 4.3 billion graduations per channel. Such high graduations can neither be printed nor observed on a standard screen in a satisfying manner. Therefore, these images have to be transformed into new images characterized by a normal number of tonal values (so-called low dynamic range / LDR images); LDR images can be visualized on a normal screen or printed out by a normal printer. This separate step in image processing (tranformation of a HDR image into a new LDR image) is called tone mapping. When the tone mapping is adequately carried out, the resulting final image shows more tonal nuances, sharpness, and detail in fine structures, and it is free from any visible over- or under-exposed zones. Also very low natural differences in brightness, corresponding to minimal differences in density and very discrete local phase shifts, are transformed into high contrast.

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  2. JHiem

    How does this sharpening compares to sharpening done by “refocusing” software (such as Focus Magic or Topaz…etc.)that sharpens images by deconvolution (at the user specified 1 to 2 pixel level?).

    Traditionally, software that “sharpens” by increasing local contrast causes “artifacts” in addition to “halo effects”, when overdone. Deconvolution software avoids these 2 problems all together and seems to result in a more natural looking sharpened image without the unwanted side effects.

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    1. pvdhamer Post author

      This is indeed (in my opinion) increasing local contrast. The algorithm claims to be low on artificacts like halos. You can do much more extreme things with the LR4/LR5 clarity filter than just minute amounts (1-2 pixel) sharpening. You can change the appearance of a thumbnail preview of a 20 MPixel image in ways that photographers normally associate with HDR software. Note that deconvolution of 1 or 2 pixels may not look like it gives artifacts, but for images with foreground/background you will get artifacts as the deconvolution would require different functions for foreground/background.

      Apart from speculation (this is a tricky field, and we are discussing a wide range of algorithms here), the bottom line is simply to try it out. This Laplacian Pyramid thing and more traditional sharpening can both be found in e.g. Lightroom 4/5.

      Reply

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