Hi Liz and all, Equalight is one of several well-regarded tools for what's often call "flat-fielding" exposure across the full extent of an image: in effect, pixel-mapping any uneven illumination or lens-based falloff based on reference to an exposure made of an unvaried sheet of (nearly) white board or other smooth, non-shiny material, and then using that reference shot to compensate for that variance across the captured field in an identically configured shot of an object. This is, as you note, an algorithmic process, but it's useful also to note that this is in the sense of algorithmic addition/subtraction of pixel exposure values based on an actual reference shot, as distinct from algorithmic processing based on software modeling of how a certain lens is believed (but perhaps not definitively known) to behave in a given context; so in that sense, it's especially closely grounded in shot-specific empirical data.
Provided it's used properly, this can be an excellent post-capture way to remove artifacts of real-world uneven lighting and imperfect lens performance, when those factors can't be fully or sufficiently dealt with in the physical world before and during capture. A key thing here is "properly": for example, because the applied compensation is based on a reference shot captured with one particular focal distance, field of view, aperture, light positions, etc., any change to any of those or certain other shooting parameters requires a new reference capture--without which, the software would be modifying an actual capture by applying compensation based on an irrelevant reference shot, and for that reason effectively corrupting rather than correcting the shot you care about. As another example, it's important to apply blur (with appropriate parameters) to the reference shot before feeding it to Equalight, so you don't end up (mis-) "compensating" based on spatially tiny exposure variances that are in fact due to how the reference board's surface (tooth) catches light...whoops...not so good to apply that to object images! Whether Equalight is a good thing to use depends on factors ranging from how even the actual lighting can be made, how the lens performs (e.g., in regard to any falloff or incipient vignetting) at the specific settings to be used, how rigorous the photographer is about using these tools well, etc. As a starting point, though, I'd tend to take a photographer's familiarity with it as a promising indicator of experience with, and care for, accurate and consistent capture, and I'd then ask how she or he typically uses it, to ensure that it is indeed in ways that will reduce artifacts and increase accuracy, rather than the reverse. Hope this helps! all best, Rob Rob Lancefield (mobile) On Mon, October 22, 2018 7:55 pm, Liz Neely wrote: > Hi MCN-L (especially imaging pals), > > While I know what I want as outcomes from my collection imaging projects, I > admit not to be an expert on the ins and outs of all the tools available in > the digital capture process. > > We at the O'Keeffe are embarking on some collections imaging with a > contract photographer who uses a tool called Equalight (3) from Robin Myers > Imaging (http://www.rmimaging.com/equalight.html) to algorithmically deal > with light fall off. > > We want to use the images from this project for print reproductions, > banners and signs, online collections, and for scholarly digital publishing > (through our in-progress IIIF server). (all the usual stuff - in print and > online) > > Knowing the museum's various desires for outcomes from this photography -- > do the imaging experts on this list have opinions / experiences they'd > share about using this type of tool? > > If you'd rather share opinions with me off-list, email me directly! > > Thank you! > Liz > > Liz Neely > Curator of Digital Experience > Georgia O'Keeffe Museum > Santa Fe, N.M. > _______________________________________________ > You are currently subscribed to mcn-l, the listserv of the Museum Computer > Network (http://www.mcn.edu) > > To post to this list, send messages to: mcn-l@mcn.edu > > To unsubscribe or change mcn-l delivery options visit: > http://mcn.edu/mailman/listinfo/mcn-l > > The MCN-L archives can be found at: > http://www.mail-archive.com/mcn-l@mcn.edu/ > _______________________________________________ You are currently subscribed to mcn-l, the listserv of the Museum Computer Network (http://www.mcn.edu) To post to this list, send messages to: mcn-l@mcn.edu To unsubscribe or change mcn-l delivery options visit: http://mcn.edu/mailman/listinfo/mcn-l The MCN-L archives can be found at: http://www.mail-archive.com/mcn-l@mcn.edu/
