Non-destructive editing stores the post-production steps without modifying or requiring a duplicate copy of the original material. This makes grading fully reversible, maximizes image quality and reduces storage requirements. In this article, we'll discuss the file formats that make this possible, along with comparing the workflow to traditional editing.
MOTIVATION
Destructive editing happened with early film whenever the original reels were physically spliced to change the sequence. With digital footage, editing is described as being destructive whenever image data is altered over the course of each post-production step even if the file is a duplicate of the original footage. This is because the process is irreversible, and each step progressively degrades the digital information especially if any of these is later undone:
RMD FILES & METADATA
To solve the problems of destructive editing, digital files are effectively appended with an editing recipe that can be applied later leaving the original image information unaltered. The steps in this recipe are based on standardized tools, such as white balance, color saturation and curves, so these can be stored textually. Copies or layered versions of the original therefore aren't required, and disk usage isn't appreciably increased.
With RED®, the original raw capture is stored as an R3D® file. The non-destructive recipe is stored as "metadata" in a separate RMD file that shares the same directory and base filename as the raw capture. For those familiar with stills photography, this is analogous to how Photoshop stores XMP sidecar files alongside RAW images. Similarly, the RMD files can also contain multiple independent editing versions or "looks."
An added benefit is that non-destructive editing gives virtually instant feedback about intermediate editing steps, since only on-screen previews need to be rendered. The metadata only converts the entire file when the footage is exported to another format, and does so all in one step to minimize any potential degradation.
IN PRACTICE
All changes using editing tools available within REDCINE-X PRO® are stored solely as metadata, and this is automatically saved to corresponding RMD files by default. Metadata can also be saved as a preset within REDCINE-X, which can then serve as a starting point for grading new footage. Each is illustrated below:
Presets can also be batch applied to a series of dailies either in full or only using selected editing steps. Even better, these presets can be directly uploaded to the camera so that the LCD screen can show custom grading with live footage:
This can be accomplished by selecting "File > Save Current Look for..." from the top menu in REDCINE-X. Click the video thumbnail below to see a quick 2 minute demonstration:
TIPS & SUMMARY
The key is to ensure that all corresponding R3D and RMD files are stored in the same folder. Otherwise REDCINE-X and other software may have problems associating each clip with the appropriate grading settings.
Despite the widespread applicability of RMD files, also keep in mind that not all editing can be stored as metadata. Some visual effects and other non-standard editing steps are only possible on output, for example. In that case, RMD files would still be used to store all of the initial steps, and any remaining steps would be applied on top.
Overall, non-destructive editing is critical when maximal quality and efficiency are important. Professional stills photographers have therefore been enjoying these benefits for many years. With the advent of digital cinema, RMD files are making this process easier with motion capture as well.