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Range Scaling Between Log Signals

When creating or using LUTs that encompass log formats, one needs to be conscious of and properly account for any differences in the data range of various log formats. There are two main ways that a signal (either log or “video”) can be encoded into integer data to be transmitted either “on the wire” or as  a file. Unfortunately, there is no consistency as to what the names of these two encodings are, and the same names are sometimes used to mean the opposite thing.

For example, one frequently seen nomenclature utilizes the symbols EE and LL. EE, or “Extended range in, Extended range out”, takes 64-940 SDI range (0-100%) and scales it to 0-1 before applying the LUT and then scales back up to 64-940. LL, or “Legal range in Legal range out”, applies the LUT directly to the the original SDI code values.

A good double-check of whether you are using the correct version of a LUT is to overexpose an image and look at it through the LUT on a waveform. ACES ODTs roll off to 100%, so if you see “super-whites” in the image, or if the whites peak below 100%, it is likely that you are using the wrong version of the LUT.