14. December 2015 15:03
Written in MATLab, this great new tool can be used to match the colors of one image with that of another, with great accuracy. While this has a great many applications, it is also useful to Star Wars fans, struggling to color correct the official Blu-rays and DVDs to match the original versions they grew up with. It can also be used to match the colors of your replacement shot (where Greedo doesn't fire his blaster, or the Land Speeder cruises into Mos Eisley without being molested by CGI dinosaurs) with the surrounding footage, for a more seamless integration.
Here are some quick examples:
This is a scan of a 35mm frame from a theatrical print by Team Negative 1:
And here is the same frame from the Blu-ray:
Using Dr. Dre's tool, we can easily match the Blu-ray to the 35mm colors:
And since the latest version allows you to export the color change data as a LUT (lookup table), you need only match a single frame from each shot, and then can apply the LUT in DeVinci Resolve to an entire scene.
Any arguments over whether or not the Team Negative One scan, Harmy's Despecialized Edition, or your favorite laserdisc/VHS copy has the "Correct" colors is neither here nor there - using this tool you can recolor the Blu-ray or any version to match your own ideal Star Wars "Look". All you need is some sample frames from your preferred source.
Here we test it with a shot from an old, red faded print, and the results are very promising indeed...:
Look for more samples and tutorials on how to restore Star Wars, as soon as I can find the time to make them! In the meanwhile, I encourage you to download this tool and play with it.
ColorCorrectv1_2_pkg.zip (182 mb)
Extract the .exe file from the zip and run it to install the MATLAB runtime environment. In the directory where you downloaded the file to (and ran it) you will now find a new file called ColorCorrectv1_3.exe. You should be able to right click on it, and Run As Administrator, but that didn't work for me. I had to copy the file to:
C:\Program Files (x86)\MATLAB\MATLAB Compiler Runtime\v714\runtime\win32
and run it from there (as Administrator) to make it work. The UI should be fairly self explanitory as it is just a set of buttons that you push more or less in order from top to bottom.
- Select a test image. This is the image that you want to change the colors OF. A figure will open, showing the image. You will be able to crop the frame, with your cursor. If you don’t want to crop the frame, close the figure window to be able to continue.
- Select a reference image. This is the image that you want to change the colors TO. A figure will open, showing the image. You will be able to crop the frame, with your cursor. If you don’t want to crop the frame, close the figure window to be able to continue.
- Build a color correction model. There are two model options: multi color space model (default), and single color space model. Multi space color space model is much more accurate, but also much slower (factor 10). Depending on the resolution/size of the images after cropping and your hardware, this may take 0-15 minutes (15 min for a 4K image) on an Intel Core i5. A figure will open showing you the test frame as it is being matched. With each iteration it should be closer to the reference. There is a stablization parameter that can be increased if there are artifacts in the colormatch/prediction. This may happen when color differences are extreme.
- Save the color correction model for later (optional).
- Import a color correction model (optional). Use this if you have already done steps 1-4 for an image in this shot and want to use the same settings again, e.g. for another shot in the same scene.
- Import any number of images, and color correct them with a color correction model you just built or imported. This will adjust all of the selected images to match the reference frame you selected in step 2. The images will be saved in a newly created directory named “Corrected” with the same name as the original images. Color correcting a frame may take anywhere between 5 and 20 seconds, depending on the resolution/size of the frame, and of course your hardware.
- Export a 3D LUT (lookup table) for use in other software programs, like Adobe After Effects (optional). For correct use, choose the sRGB setting in the software you want to use to import the LUT.
When building a color correction model you should consider the following:
- The model assumes the test and reference images (frames) are identical, aside from the color. In other words it’s important the images are cropped in the same way (to a reasonable degree). Incorrect cropping may lead to artifacts.
- When using a print or a low quality source as a reference, there may be color variations within the frame. For example some parts may be darker or brighter than others. If you use the full frame for building a color correction model, it will try and fail to reconcile these differences, resulting in artifacts. The best way to go, is to select a consistent part of the frame, select the same part for the reference, and then build the color correction model.
- In theory you can match any source to a reference, but there are limitations in practise. You have to consider that a limited color depth may result in artifacts. Crushed dark colors or blownout light colors are notoriously difficult to regrade, but they also may affect the color matching in other areas of the frame. In such cases increasing the stabilization parameter should reduce artifacts, but they are sometimes unavoidable.
- Although you could regrade an entire film, based on a single reference frame, this will probably not work in practice, because one reel may have degraded in a different way than another or one scene may have been color graded differently from another. In principle it is possible that each frame will have to be matched individually, but usually a film is graded on a scene by scene basis, so a single reference will suffice for a particular scene.
Please visit the original thread on OriginalTrilogy.com to learn more, or to contact the author of this tool.