Deinterlacing
Deinterlacing methods are used to process interlaced video signals (480i/576i), common in high-resolution modes for Sega Saturn, PlayStation, and PlayStation 2. Without deinterlacing, movement causes "combing" or "judder" artifacts on progressive displays. While there are some attempted shader-based solutions, emulator's built-in deinterlacing methods provide better results on image quality.
Before diving in
Algorithms
Bob Deinterlacing
The most common and fastest method. It separates the two fields of an interlaced frame and scales them to full height.
- Pros: Zero lag; preserves the "flicker" look of original hardware used for transparency effects (e.g., shadows in Silent Hill 2).
- Cons: The image "bobs" or shimmers vertically because lines are offset between fields.
Weave / Blend
Combines two consecutive fields into a single frame.
- Pros: High detail on static images.
- Cons: Severe "combing" artifacts during horizontal movement; generally not recommended for gaming.
Motion-Adaptive (MAD / YADIF / BWDIF)
This algorithm analyzes pixels across multiple fields to determine if they are static or in motion. These are more complex shaders that attempt to detect which parts of the image are moving. They use "weave" for static areas and "bob" or interpolation for moving areas. As of 2022, PCSX2 and high-end shader suites use Motion-Adaptive Deinterlacing. BWDIF (Bob Weaver Deinterlacing Filter) is a modern evolution of this, providing sharper edges than YADIF.
- Pros: Uses "Weave" for static areas (preserving full vertical resolution) and "Bob" or interpolation for moving areas. Effectively eliminates shimmering on text and UI while removing combing on moving objects.
- Cons: Can introduce a small amount of input lag and requires more GPU resources. Moving objects may appear slightly "softer" than static ones since they rely on interpolation.
Motion-Compensated (MC)
The most advanced deinterlacing approach at this moment. Unlike adaptive methods that just "switch" techniques, MC uses "Motion Estimation" to track objects moving across the screen and "reconstructs" the missing data by looking at where those pixels were in previous/future fields.
- Status: Primarily found in video post-processing (e.g., QTGMC, FFmpeg). Not yet viable for real-time emulators due to extreme GPU demand and the necessity of "looking ahead" at future frames, which causes significant input lag.
- Pros: Near-perfect reconstruction of moving images; provides full vertical resolution even during high-speed motion (the "holy grail" of image quality).
- Cons: High computational cost; prone to "hallucinating" or warping artifacts if the motion estimation tracking fails.
Other approaches
Automatic
Modern emulators can now automatically toggle deinterlacing based on the game's internal state.
- How it works: Instead of a "one-size-fits-all" shader, the emulator detects when a game switches from 480i (interlaced gameplay) to 240p (progressive menus) or 480p (progressive scan) and disables deinterlacing automatically to prevent unnecessary blurring.
Index/compatibility database
Modern emulators can now automatically toggle deinterlacing based on their index/compatibility database.
No-Interlace Patches
A popular alternative to shaders. These are community-made patches that modify the game's code to render in progressive mode internally.
- Pros: The cleanest possible image; removes the need for deinterlacing shaders entirely.
- Cons: May cause graphical glitches in specific titles or break FMV playback.
Gallery
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Interlaced Artifacts
Example of "combing" during high-motion scenes without deinterlacing. -
Bob Deinterlacing
Eliminates combing but introduces vertical jitter/shimmer. -
Motion-Adaptive (MAD)
Modern standard that preserves detail on static objects without shimmer.
Links & Resources
- PCSX2 Motion-Adaptive PR: Pull Request #7376 Details
- Deinterlace (Bob): Basic method for low-spec hardware.
- No-Interlace Patches: PCSX2 patches repo for 480p/240p forcing.