LUTs in Tech Industry
Ever since the launch of photo filter and beautification apps, folks in the tech industry are doing all sorts of things around filters. Color filters are one of them. But the funny thing is, color filters can be implemented in mobile apps in a lot of ways. Let’s explore some of them:
- RGB Spline Curves: This involves plotting value coordinates for each color curve. Things like brightness, saturation, and contrast have to be mentioned separately in code.
Curves: Composite (0,38), (63,66), (195,191), (255,219)
Curves: Red (0,15), (101,92), (129,129), (255,255)
Curves: Green (0,15), (85,65), (128,128), (255,255)
Curves: Blue (0,10), (59, 70), (158,170), (255,245)
As you can see, for complex curves the number of values that needs to be plotted will become a nightmare for both designer as well as the dev.
- Adobe Photoshop curves (ACV): ACV is more or less the same. It’s an adjustment layer in Photoshop that can store the spline curve values in it. But now, a designer no longer need to note down each and every coordinate. The only catch with this is that both Android & iOS needs a third party library integration to support/read an ACV file. Which will increase the overall size of compiled app plus, it introduces third party dependency.
- Look Up Table (LUT): One of the reasons the tech industry started using LUT is when they noticed a lag in switching between filters. This is because, at a given point in time, a mobile app is always running a lot of background processes — this makes filter applying an extensive battery consuming task. LUTs can be stored as .png/.3dl/.cube.
Creating LUTs using Photoshop
It can be said that LUTs in Photoshop (Ps) is somewhat like a hidden gem. It is completely possible to create a stellar photo effect using Ps and save it as a single LUT file. Check out the tutorial shown down below which uses a mix of adjustment layers such as Curves, Channel Mixer, Gradient Map, Levels, Black & White, and Color Balance to create the desired effect and then combine all of that in a single layer using LUT. All inside Ps.
In short, once you have played around to get the final effect, with your background layer locked and adjustment layers ready to go, click on File, Export, and then Color Lookup Tables. From there Ps will ask for a description, quality, and format. The suggested method is to lower the quality to Medium or High rather than Maximum and to use CUBE instead of 3DL (CUBE is more widely accessible across other applications). Rename and save this LUT file where you want to.
LUTs using PNG (Hald)
Hald is a graphical representation of 3D LUT in a form of a color table which contains all of the color gradations of 3DLUT. If Hald is loaded into editing software and a color correction is applied to it, you can use 3D LUT Creator to convert your Hald into 3D LUT and apply it to a photo or a video in your editor.
In simpler terms, it is a 3D LUT converted into 2D image as JPG or PNG file. Hald is a pattern containing all color values (pixels) for a specific size of grid. Bigger the grid, better color accuracy in the output result. Bigger grids have lesser interpolation of values as compared to the smaller ones but are heavier to load into the system as a tradeoff.
Effects are applied over a neutral hald file and saved using Ps to get the final LUT. Neutral hald files of different grid sizes shown below: