Photo courtesy of Spectracal
UPDATED: 7/27/2015 : Many EVF (electronic viewfinders) and on-camera monitors (such as those from Atomos and SmallHD) have built-in technology to allow the use of LUTs on-set. The use can range from simply providing a display LUT, so you can focus and expose properly while recording a log \ flat image, to actually burning in a creative look into the footage being recorded.
The word LUT may have lost all meaning to you, or it may mean numerous things, aside from it's actual definition of "Look Up Table". I'll try & explain it before we move forward, as it's important to realize how limited LUTs are. A LUT is nothing more than a massive set of pre-calculated numbers for both input and output colors, or a long list of "this green #1 turns to into green #2" style equations. I am simplifying this significantly, but I am trying to make a few points about LUTs in general before I go forward and abuse them for our creative intentions. You give a LUT a color and it mathematically hands back another color, no matter if it's applied to Canon DSLR, RED, Alexa, scanned film footage, etc. A LUT is a stupid mathematical conversion & has no idea what it's being applied to. They're created for ONE specific purpose, whether to emulate\prepare for a film print (sample LUTs, FilmConvert, Impulz), convert between a LOG format and Rec709 (HDTV) for a specific camera, or provide a creative look (OSIRIS, Blockbuster LUTS, ). Okay, long story short: LUTs are stupid math-based color conversions that don't know anything about what camera or format we're using, what color space we're in (LOG or REC709), how the footage was shot\lit\exposed yet many believe they are "magical one-step color correction" machines. Now that we know that's not so, how can we use them creatively while understanding their limitations?
Note: I wanted to mention FilmConvert at this point, as its essentially a on-the-fly LUT generator that's been programmed to adjust it's curve based on the input camera and the "output" film emulation (so actually 2 LUTs), but its still essentially a LUT for our purposes.
LOG OR NOT? - With YouTube, Vimeo, and forums galore spreading different information, this has become a very confusing subject. If your footage was shoot on a Canon or Nikon DSLR, even with a picture profile like Cinestyle, VisionTech, Prolost, or many of the others low contrast picture styles, I highly recommend you do not treat this as "LOG" and treat it as Rec709 footage when choosing "creative" LUTs that require a choice. That being said, if there happens to be a specific option for that profile\setting, proceed to use that one, of course. The exception to this is some of the newer cameras like the Sony A7s, which comes with proper S-Log2 can be treated as LOG. You can tell because the feature is ALWAYS inherited from the higher end models from that manufacturer.
One of the original "true" purposes of LUTs is to convert between video gamma formats, such as converting Canon C-Log, REDLogFilm, BMDFilm and LogC to Rec709 (HDTV standard). I've likely left out several LOG gamma types, but you get the point. Most camera manufacturers will provide a "normalization" LUT, or several in the case of Arri and Blackmagic, that allows a direct conversion of the image from the "milky", low contrast log footage captured in camera (which allows the camera to record the most image data) to a more "contrasty" and saturated Rec709 standard, WITHOUT any other changes. No creative additions are made by using these LUTs. These are very useful in establishing a good base image\set-up for grading a LOG footage, as you can simply focus on color having already converted the image from LOG gamma to Rec709.
If your are working with RED footage in REDLogFilm, Alexa footage in LogC, or any Blackmagic footage in BMDFilm, proceed to use LOG based LUTs for contrast expansion & the color effects in one step. If you'd like more control, you can use a technical LUT to convert your LOG footage to Rec709 and then use Rec709 "look" LUTs, as this will provide a more subtle look.
Here you can download a set of generic Rec709 to Log (technical) conversion LUTs, if you'd like to try working with your footage in true LOG but shot in standard Rec709 or if you're unable to shoot in LOG. Just be aware, 8 bit DSLR footage will not fair well with this harsh of a post correction. These conversions is best served for footage that is 10 bit or higher. Thanks to Juan Melara for the conversion LUTs and huge thanks to Stephanie Duchaine for being our model for these tests. We'll hopefully be seeing more of her in future content!