Looking at Lookup Tables (LUTs)

A while ago, I began hearing a term that I wasn’t familar with:  lookup tables (LUTs).  Curious, I “looked up” the definition, and was mildly puzzled to see it defined as a series of values in table format that helps you interpret or translate another set of values.

Image DataWhat does that have to do with photography?  As it turns out, every part of a digital image is a set of values – for size, dimensions, camera settings, colour space, etc.  We’ve long had the ability to manipulate any one value to our liking through the sliders we see in modern editing software.  Now it seems we also have the ability to redefine broad swaths of data at once.  Find out how.

Lookup tables (LUTs) are a computer processing invention, designed to provide an efficient way for computer programs to reference repeated actions without the need to code every action every time.  Instead, the code is written once, assigned an identifier and a place in a table, and referenced by other lines of code when needed.

Excel spreadsheets, in wide use for both small and large datasets and calculations, include “VLOOKUP” and “HLOOKUP” functions that serve exactly this purpose.  But same question:  what does that have to do with photography?

3D LUTColour grading has been a component of motion picture and video production for a long time.  It ensures that the whole product has a predictable consistent look.  It seems that today this is achieved by using LUTs to interpret and redefine colour values across an entire scene.

It also seems that LUTs found their way into the interpretation of photographs from space.  To save storage and transmission time, and to investigate specific phenomenon, objects are often captured in multiple series of images taken at different wavelengths.  The original images contain a goldmine of scientific data.  But for presentation purposes, the bland and uninteresting (to us lay people) monochrome images of deep space are redefined and suddenly explode with colour once interpreted by a digital editor and a set of colour translation tables.

So it was just a matter of time before mass-market digital editors adopted lookup tables.  LUTs first appeared in Photoshop with version CS6 in 2012.  Most people apparently had no idea they were available.  But they do now.  And there are now lots of training tools to support them.

Matt Kloskowski tells us that LUTs can be saved once created, and transferred to any software capable of referencing them.  That makes them unique – most user generated profiles are not transferable across platforms.  Matt published an introduction to LUTs for Photoshop in 2017.

As Matt explains it, the difference between LUTs and any other presets that might be defined in Photoshop is that LUTs are specifically for colour and don’t affect the exposure/brightness values in the image.  The only thing that changes is the colour.  That’s another feature that makes them unique.

Glyn Dewis also offers a great introduction to LUTs in Photoshop.  Glyn notes that Photoshop doesn’t provide a preview of the colour change before you apply it, but he demonstrates a technique for creating previews to make sure the colour is perfect before you say yes.

Glyn uses LUTs in much of his retouching and the effect is exactly as intended.  It creates mood, context and richness in the finished work.  In his case, they are often used to add a sense of history to a photograph.

I have one problem with these videos though.  Like many of the options for editing in Photoshop, the effort to use them should be proportional to the level of control the maker prefers to have over the final look of the image.  The number of clicks required by the maker in either of the above videos to achieve that end result is, in my view, far beyond what most people are willing to do.  If anything, software is moving in the opposite direction, away from requiring a click-fest to fine tune an image.  Movie studios might need it, but the rest of us don’t.

As an alternative, other software, such as ON1, has also leveraged LUTs and include a LUTs filter, which provides colour-graded looks as previews.  The maker scrolls through the options and picks the one they like.  The filter also allows for blending and masking of the result, just like any other filter.  LUTs may be imported and appear in the previews with all the others.  The simplicity of use, combined with the quality of the end result, make this approach much more appealing.

Suffice to say that more and more options are becoming available to photographers to get the perfect result.  The choices seem almost endless now.  LUTs are just another piece of that puzzle.

The purists might say that it’s almost too simple now – you push a button, see your choices and apply the one you like.  You don’t need to learn the alphabet any more; you just imagine the story and the book writes itself.  I don’t mind that at all.  I’d rather imagine than click.