LUT confusion

[Jed Shepherd]

So im a bit confused about the use of LUT's.

In color i can import the standard LUT which comes with color which makes redlogfilm images appear to have proper gamma? again.
My confusion comes from that I can also achieve a better looking image by using a curve. My question is, are LUT's used to view the image while doing color work then removed before export and print to film? If so, seeing as i am exporting to dvd, blu-ray and HDCAM, should i just ignore LUT's and use a curve or am I getting this all completely wrong?
I did some reading on all of this but some of the answers were quite complicated and I'm still not sure.

Any help/explanation would be great.
Thanks

[Jake Bastian]

What is the standard LUT that comes with Color? What you're looking for is a Cineon to Rec. 709 LUT if you're going straight out to Blu-ray. If you don't like the way your image looks with the LUT applied you should keep grading till it looks right as the point of a LUT isn't to get a more visually pleasing image, it's to get an image whose color values are a known quantity so you can maintain image fidelity as you apply transformations to get them into your other formats.

[Jed Shepherd]

The LUT that got installed with color was one called log_95_685.mga. Its not that i dont like the way it looks, its just that my image looks very similar with the LUT as when i apply a curve. Does a LUT just show you what the image will look like with the for example rec.709 space? If so when im done correcting will the send back to FCP have the LUT removed or still imprinted?

[Jed Shepherd]

Ok so a LUT is used on a non calibrated monitor? Im using my macbook pro right now to muck around but I will be grading on a system that i know has dual apple cinema displays but also a third monitor which i believe is a calibrated broadcast monitor. How do i tell if I can trust what im seeing on the third monitor? Also a bit confused about the using LCD's issue. Does a rec.709 LUT provide a proper image through a cinema display for instance or is CRT the only way to view anything properly?

[Jake Bastian]

Yes. So if you have a cineon file in linear space and your primary destination is HDTV you would put the LUT on so that you can see what your image will look like in Rec. 709 space while grading. Depending on where you're going from there you can either bake the LUT into your file or take it off and leave yourself with a linear master that you can then apply other LUTs to in your finishing system to send the file to multiple formats. The other option in that case would be to apply a LUT to your monitor so you don't have the risk of affecting your file by accident (say you forget to remove the LUT before export).

[Jake Bastian]

What monitor are you using for calibrated viewing?

[Jed Shepherd]

Im not sure of the monitor or if its even a broadcast monitor. Supposing its not, is it possible to download a free rec.709 LUT from anywhere? I went through digitalpraxis.net but their free LUT's seem to all be print LUT's.

I will check tomorrow what monitor it is and if its meant to be calibrated or not.

[Jake Bastian]

You can get a LUT generated through ARRI that will convert Alexa Log C to Rec. 709 which is pretty close to what you're looking for. Without a proper monitor I'm not sure using LUTs is going to be very effective for you though...

[Jed Shepherd]

Ok. I think im getting confused here. So a LUT only works on a calibrated monitor? I for some reason was under the impression that it emulated a calibrated image on a non calibrated monitor.

[Jake Bastian]

You'd need a lot of expensive equipment to pull that off. Someone would have to come in and profile your monitor and generate a LUT based on those pixel values - or you could do it yourself if you had the right software and setup. A LUT you get off the net can't tell what pixel values your monitor is displaying it operates under the assumption your monitor has been calibrated to a specific profile.