Two of the main issues that you certainly will come across when shooting with a low-resolution camera (even with a 4K camera in some cases) that records 8-bit video are the moire and banding artefacts. Whereas the latter can be overcome with a unit that simply provides higher bit-depth, certain post-production techniques can help you to reduce the nasty moire patterns considerably.
Below D.L. Watson showcases an efficient workflow in After Effects that minimizes the effect of these artifacts when particularly dealing with a Blackmagic Pocket Cinema Camera footage. Of course, the method might not completely remove the issue, but it will certainly make it less noticeable. And the great thing is this technique can be utilized for other cameras which have the same problem.
To get started, just open your BMPCC DNG sequence or a ProRes file in After Effects. Before you drop the files in a new composition make sure that you set the Color Depth to 16-bit. You can access this setting in the Project Settings. Once you’ve dragged the clip to your composition, zoom in and look for the problematic areas in the video that need to be treated.
Further, create a new Adjustment Layer. Now, go to Effect in the main menu, navigate to Blur&Sharpen section and choose Gaussian Blur filter. Set the Blurriness to 5, go the Adjustment Layer Settings and change the Transform mode from Normal to Color. This way the Blur filter that you’ve just applied will affect only the Color Channel, not the Lumenocity of your clip. This workflow should instantly eliminate most of the nasty moire colour shimmering that you see in your video.
If you want to take the process one step further, you can track the movement of the problematic areas of your clip and apply the effect only to those specific areas of the video. Once the Tracker completes the processing, you need to create a Null Object and apply the tracking data to the Null Object. Create another Adjustment Layer and make sure that you parent it with the Null Object.
Apparently, this step will allow you to apply the effect along with the camera movement. Utilize the Pen Tool if you want to create a mask around separate parts of the image that need to be processed. In general, try to reduce the moire artifacts and use this technique before doing any colour correction or colour grading to your footage.
Another approach to deal with moire artifacts suggests using the same method, but this time, you may want to use the Median grain filter instead of Gaussian Blur or Tint.
Either way, you’ll be able to achieve decent results and get rid of the moire, or, at least, make the footage usable for your project.
[source: D.L. Watson, Zura Lomidze]
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