LUT 3D Knowledge

Show lookup table (look-up-table) referred to as Lut,lut

A LUT is essentially a ram. It writes the data beforehand to ram, each time enters a signal is equal enters an address to look up the table, finds the address corresponding content, then outputs. LUT (look-up table) is actually a pixel gray value mapping table, it will actually sample the pixel gray value through a certain transformation such as threshold, inversion, binary, contrast adjustment, linear transformation, etc., into another corresponding gray value, so as to play a prominent image of useful information, Enhance the light contrast of the image. Many PC series cards have 8/10/12/16 to 32-bit lut, which is defined by software specifically in the Lut.

Digital intermediate, referred to as DI, has encountered a difficult problem when it began to appear a decade ago, that is, how to make interactive color matching for different devices. At this point we found the LUT mapping table. Now, Lut is almost everywhere, But there are still a lot of people who don't understand it. As a digital film consultant, I often get calls or receive emails, and many people ask me how the LUT should be used. I think the question is more complicated to explain.
What is a lut?
A lut is just a table, a mapping table. In theory, it's just a text file or a spreadsheet full of numbers.
Here is an example:
4095 0 4095
4095 0 4095
0 1535 0
0 1535 255
0 1535 511
0 1535 767
0 1535 1023
0 1535 1279
0 1535 1535
0 1535 1791
0 1535 2047
...
The concept is simple, in each line of input a value, there will be a corresponding value output.
For example, enter:
r,g,b=232,121,211
It will output:
r,g,b=243,92,176
It gives us a different color.
The LUT mapping table mainly applies mathematics knowledge, it seems to have nothing to do with color knowledge.


Kodak's test: Simulate different film styles through a lut.
Two different digital mid-slice technologies
There are two common workflow processes for digital intermediate-slice technology:
The first is to use Rec709 's color space standard directly on the monitoring device to process film images that have been scanned into digital files.
Advantages: Simple process.
Cons: The Rec709 color space has limited latitude to reproduce all color information in the film.
The second is to use a color grading system to convert a movie into a digital signal output. This approach is more complex than the first.

Advantages: Good color reproduction, less loss of color information. The image processing can achieve high quality.
Cons: Complex processes,
Another way is to create a "zebra" LUT, which will tell you which color information for the film will be lost in post-processing.
The other Lut
There are two main types of original files that need to be color graded: Digital video files and digital images for film scanning. Most monitors use cathode ray tubes, making it easy to achieve HD Rec709 color space.
Today, for different needs, we need more different lut:
* Lut in a digital camera: You can synchronize the color space in the camera and post-production.
* Onset/offline Lut: If you use footage of a camera-specific encoded format (for example, Panavision Genesis Panalog), importing the appropriate LUT during post-processing can get a better color reduction.
* Used to display the LUT: In today's different display technologies, if you don't use a lut, they won't be able to restore the Rec709 effect to their display terminal.
3D LUT
Now people are already doing some 3D Lut, but 3D Lut is just a new rendering method for Lut.
* One-dimensional Lut (1D lut) affects all channels, and technically it only affects gamma.
* The two-dimensional Lut (2D lut) has no interdependence between the channels, and they are handled independently. This means that you cannot really handle or prohibit colors that are not likely to exist.
* Each coordinate direction of the three-dimensional Lut (3D lut) has an RGB channel. This allows you to map and process all of the color information, whether it exists or not, or where the film is not up to the color gamut.

The future of Lut
Once the film is gone, the era of digital cinema will come and we will save a lot of trouble. Today, many companies are already considering whether their films are made using a full-digital process.
Display technology standards are difficult to unify, many different companies have different color management standards. For example, a video that plays on a projector and plays on a liquid crystal display or on a CRT display will show a different color, which is a bad thing.
Therefore, we can not be separated from the lut for a moment. More importantly, LUT has become a standard and basic way for many industries to manage color.