joe12south wrote:I'm debating building a BMD Color Science 4 > Arri Alexa LUT. (More of a "stylistic" LUT than one claiming to do some voodoo that turns a P4K into an Alexa.) Does anyone know if one already exists?
If you look around online you'll see some colorists demonstrate a method for doing it by using Color Space Transform to go from Pocket 4K (or any other log source image) to Alexa Wide Gamut + Log C and then adding the Alexa REC709 LUT. However, there are some caveats:
1) While in theory it gets things close, it isn't an ideal way to work with files from any camera. The transform is likely to exacerbate noise or introduce clipping at the edges of the gamut.
2) The Color Space Transform OFX defaults to assuming 6000K source when it does the math, so the results will be worse for tungsten compared to daylight.
If your desire to match the Alexa is for a shoot that includes both cameras, it's much better to shoot some good color charts (DSC Labs makes really good ones) on both cameras and match the images manually. Using Davinci Color Managed mode may make it easier, depending on the look you want to achieve. Eventually ACES will be another color managed option, but BMD hasn't yet added an IDT for the 4K Pocket.
If your goal just to quickly get a good look out of the Pocket 4K, I honestly feel that the new BMD Extended Video, either set in the RAW tab for cDNG files, or added as a LUT to ProRes film mode files, is a great starting place for a grade. It will yield a cleaner result than trying to cram the image data into the Alexa LUT through Color Space Transform.