Re: [MCN-L] Imaging opinions on the Equalight 3 Tool
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/
Re: [MCN-L] Imaging opinions on the Equalight 3 Tool
Hi Liz, Greetings from the Imaging SIG. Robin Myers is a respected name in the cultural heritage imaging field. His software does one thing called flat-fielding, but it does it well. Flat fielding allows a photographer to even the illumination of a flat work that was not lit perfectly evenly and correct for imperfections in lens vignetting (no lens is perfect) by photographing a large white card (bigger than the painting) under the same lighting and having the software figure out the unevenness of the lighting from that white card and apply the correction to the photograph of the painting (or drawing, object… whatever it works on various flat objects but let’s just say paintings for now…). One reason (and the fear that a lot of non-imaging people have is) a photographer might want to do that is they might not have a large enough space, enough time, the right skills, or enough equipment to completely light an object perfectly evenly, but I find that that is rare. More often I find that it is used by photographers who want to bring more texture out of the paintings. The problem with even lighting is it is very flat and doesn’t allow for the small shadows that highlight the texture of a painting. A more raking light will accentuate the texture of the painting, but it requires that one side of the painting be more strongly lit than the other. By photographing with a raking light and then flat-fielding, the photographer can get the best of both worlds, having more texture but not having it seem that one side of the painting is much brighter and the other much darker. Many programs used with higher end medium format digital cameras like Phase One’s Capture One or Hasselblad’s Phocus will have a type of flat-fielding option built in using their own names (Phase One calls it LCC and Hasselblad calls it Scene Calibration) and it’s pretty common to use one of these tools particularly on smaller works 2D works (needing a white board larger than your work makes the process less practical for extremely larger objects). But when you can use it it's one step (among others that should be also taken) that can ensure the image is best representing the colors and tones of the original work and knowing that the dark corners are what the artist actually painted and not just that the lens vignetted a little there.. As far as should you trust a photographer using the tool? It’s a tool used by many photographers that I trust. That said it is just one tool and and craftsman worth his paycheck should have a tool box with a lot of different tools for different tasks. If I was dealing with a carpenter and they were telling me about their random orbital sander... that is great they can do amazing things, but you also need a hammer and a saw and you need to know how to use them. On Mon, Oct 22, 2018 at 8:27 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/ > -- Kurt Heumiller Studio Production Manager Imaging and Visual Resources The Museum of Modern Art 11 West 53 Street, New York, NY 10019 212-708-9489 kurt_heumil...@moma.org ___ 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/
