Of course you can see that a LUT has a well defined start and finishing value, whereas a mathematical curve could be infinite. We’ll come back to this later on.Ī 3D LUT is where the ‘issues’ can start. What a 3D LUT is doing is similar, but it takes 3 values as input, a R, G and B colour value usually. Then looks those up in a table and you get a resulting RGB value. So all a 3D LUT is doing is taking a set of RGB values and returning different RGB values. A LUT is a simple way of describing any possible colour transform and has a lot of good uses. Some camera manufacturers offer LUTS to help transform their camera output into different colourspaces. Ben Turley wrote a utility called LUTCalc which offers incredible flexibility in converting between camera colourspaces, tone curves and creating correction LUTs. Arri has a LUT generator online which takes Alexa Footage and allows you to generate a LUT to transform it to Rec709 or some post production orientated colourspace. Sony offer a bunch of LUTs to again convert from camera to various display colourspaces. They take a wide colourspace of a camera, transform it to other spaces and allow you to quickly see an image that looks 'correct' on your display. LUT examples - 4 examples, from No LUT to three differnet LUTS applied. The exposure response appears different in each of these LUTs as well.Ĥ examples, from No LUT to three differnet LUTS applied. The exposure response appears different in each of these LUTs as well.īASE SRGB IMAGE - This is the control image. It has a hue circle and two others at +2 stops and -2 stops. This helps us compare LUTs like for like.ģD LUTS are often sold as ‘looks’ or ‘film emulations’, they ‘bake' in a certain look that would be very difficult to create manually. Modelling the look of a particular stock of film is a great example. The LUT can not only change colours but also the tonality of the image to something that looks filmic. Indeed the very birthplace of LUTs is to be found in the DI. When you’re working digitally the film out company could provide LUTs specific to the film stock you will be outputting so when grading you can view your image under an emulation of how it would look projected from film. Of course the usefulness of this is apparent, you can now use similar LUTs to make your digital video look filmic. And indeed there are many commercial products for doing this. Are they all wrong? Not really, they have a use. Purists will argue that anything that can be done via an emulation LUT can be graded, which is true. Lutists will argue why waste all that time. The subject of film emulation will be brought up again in another post.Ī 3D LUT is a one way street though, because once you’ve transformed your image you cannot transform it back. If you take every RGB colour and transform that to a shade of purple. Then once you’ve got your purple image how can you go back? All your pixels are now purple and you cannot separate the original colours. So 3D LUTS are usually destructive to the image. KODAK FILM EMULATION - After passing the hue circle through a Kodak film emulation lut, see how the colours have changed. This is a complex colour transform based on analysis of actual filmīut this post is pointless without examples. If you click on the image and view the full version that's better, the full versions are PNG files, so no JPG compression. You can flip back and forth to compare them as well. So here is my sample image, first of all in pure RGB goodness. To put it in perspective though, it looks to be a pretty small shift of greens in the X-axis.Full saturation, full range, bright and video at its finest. I'd hope not, but Nick I think that you are right that I should give Blackmagic a chance to chose the preferred option before pushing an update to LUTCalc. Having said that, if DaVinci has a duff matrix hard coded into it, they may well decide to fix the primaries to the matrix. In theory it could be that the matrix is right and they mistyped the primaries, but having had to track down that kind of typo, er, more than once -), and considering that the difference appears in exactly one coordinate of one primary, I'd say the primaries have been published as intended. I'd say that looks to me like finger trouble, someone typing 0.1681 when they meant to put in 0.1618 for the matrix calculations. The only difference being the X value of green. Using the primaries and white point (D65) as published, and reversing things I make the primaries and white point: Thanks for all the heads up - i can add it in easily enough, but as mentioned, the primaries / white point and matrices don't seem to hook up over the green primary.Īs they stand, I make the DaVinci-XYZ matrix:
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |