terminology

By far the best thing about all this linear color workflow stuff is that people can easily use one term to mean completely opposite things. For instance, we say that an image with a gamma of 2.2 looks right on a monitor of gamma 2.2, but in truth one of those is really the opposite of the other so that they can cancel out.*

Throb.net has a very good breakdown of using a linear-light workflow in 3D. In fact, part of it looks strangeley familiar. But in Throb’s graycard example, he uses the opposite terminology from mine.

He calls is darker card, the one that has not been corrected for display, “gamma encoded,” and calls the one that looks right to our eye “linear.” This terminology disagrees with mine, and with that of the inimitable Bill Spitzak. I like to use linear to describe linear light intensities, whereas Throb tends to use it to describe perceptual linearity.

But a perceptually linear image is indeed gamma-encoded, so I still think Throb’s page is a little confusing. I’m guessing he’s saying that the dark image you see is effectively gamma-encoded by the display device?

He and I and others actually had a conversation earlier this year on the Highend2D Shake mailing list about how corn-fusing all this stuff is. It boils down to the difference of describing the data in the file vs. the light that hits your eye. Perceptually linear = gamma encoded file. Perceptually dark = linear data.

It's always dangerous when some random website, mine included, starts claiming to be authoritative on matters of color, so I've always been carefull to be consistent with my terminology, label it as mine and not necessarily everyone’s, and declare my assumptions. Looks like Throb has a similar policy.

Lastly, I’d be remiss if I didn’t point out that there is a magnificent chapter by Brendan Bolles on all this stuff in AE 6.5 Studio Techniques.

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* And for that, I do apologize.

Comments

[ben syverson]

I'm with you, Stu -- using the term "linear" to describe gamma-encoded images is confusing, unintuitive, and contrary to industry practice...

[jcburns]

Yeah, "linear" carries for me the connotations of untouched, all-natural, no preservatives. "gamma-encoded" sounds like something you wouldn't get at Whole Foods.

(Why am I hungry at 1 am?)

jcburns

[stu willis]

The question that must be asked after someone describe something as linear is "linear to what?" Linear is a relationship between X and Y... Without knowing what *both* those things are, its a useless descriptor imnsho.: )

[Stu]

Stu, I agree, which is why I usually say "linear light" or "radiometrically linear" when striving for absolute clarity. In my nomenclature, when pixel values = scene light values, that's linear light data, and that's the only type of image I ever describe as "linear."

[stuart willis]

I prefer linear light or linear to light, simply because its more obvious than radiometrically linear... that, and the VFX Supervisor at the facility I'm at has indoctrinated us in the One True Way of naming Colourspace.

I