CRT phosphor decay simulation shader with motion blur reduction and Voodoo2-style color quantization.
Hi everyone! I'm a huge fan of classic arena shooters like Quake and Unreal Tournament. Back in the day, I even competed as a Quake 2 and Quake 3 champion. To recapture the feel of the CRT displays from my childhood, I looked for proper CRT effect shaders, but most existing options like various BFI and CRT beam emulators were either simply broken or just didn't deliver the look I was after.
That's why I decided to create my own solution: CRT Dusha (Soul in Russian) ReShade Shader. The shader simulates the phosphor decay CRTs had, which in my opinion was the soul of the lost tech (hence the shader name, Dusha). It's highly flexible and can recreate the look and feel of the monitors from your childhood, including the image produced by the greatest GPU ever—3dfx Voodoo2! RIP, but never forgotten!
- Realistic Phosphor Decay: Multi-stage Fibonacci-weighted exponential decay model simulating per-channel phosphor persistence (red, green, blue decay at different rates, matching P22 or custom phosphor characteristics).
- Advanced Gamma Shaping: Power-law gamma combined with decay can restore intended luminance curves in retro titles and bring modern games closer to analog display behavior.
- Single-Frame Processing: Shader operates on the current frame only, minimizing input lag for the most responsive experience.
- Motion Blur Reduction: Extended BFI (Black Frame Insertion) approach through multi-stage phosphor decay increases motion clarity, with richer persistence curves than simple on/off black frame techniques.
- 3dfx Voodoo2 Pipeline: Optional 16-bit RGB565 color quantization with Bayer ordered dithering (2x2, 4x4, 8x8 matrices) for mid-90s graphics card aesthetic.
- Split Screen Comparison: Displays processed and original image side by side for real-time effect comparison.
- LCD Safe Mode: Enabled by default, introduces subtle phase flips to prevent image retention on LCD panels.
- Optimized for Lower-end Hardware: Tuned for consistent performance on devices like Steam Deck OLED.
- DX9 Compatible: Shader Model 3.0 support for older games.
- ReShade 4.0 or higher.
- Steam Deck: Reshadeck (Reshade Shader Loader for Decky Plugin Loader).
- For desktop and borderless fullscreen apps, ShaderGlass in combination with ReShade can be used.
- Game/app must be compatible with DirectX 9/10/11/12, OpenGL, or Vulkan.
Like all shaders of this type, the effects are frame-based, so you need frame rate synchronization with your display refresh rate:
- High refresh rate displays and high framerate: Use V-Sync.
- Variable refresh rate displays: Use G-Sync/FreeSync with frame capping (standard 3-5 fps below the monitor's max Hz in addition to V-Sync).
- Low refresh rate displays (like 90Hz Steam Deck OLED): Aim for maximum stable fps + V-Sync (with Steam Deck Game Mode you can use Disable Frame Limit and Allow Tearing for better input lag; Gamescope has its own V-Sync always on).
Simply put: Sync your monitor refresh rate with your in-game FPS. That's the primary requirement. Otherwise, the shader is plug-and-play.
High refresh, HDR, and OLED are beneficial (effects might look and feel better) but not required. All development and testing was done on a 4-year-old 165Hz IPS panel and 90Hz Steam Deck OLED.
Besides simple scanlines and Trinitron-like vertical RGB color separation, no CRT masks, halation, or other bells and whistles are included. CRT Dusha focuses purely on phosphor behavior and motion response. You can use any mask shader you like, there are many available. I personally prefer simple Trinitron-style masks.
- For the most realistic results, apply mask shaders after CRT Dusha in the ReShade chain
- Steam Deck OLED: Use 2 frames per decay cycle (basic BFI, 1 bright frame + 1 dark/black frame) to avoid flicker at 90Hz
On LCD panels, prolonged display of high-contrast static patterns can cause ions in the liquid crystal layer to drift, leading to a DC voltage buildup inside the pixel cells. This buildup can temporarily bias the pixels, resulting in image retention (“burn-in”). This is a physical property of LCDs, not a shader issue, and it primarily appears when alternating bright and dark frames repeat in a perfectly even pattern.
Examples:
- Leaving your game paused with static high-contrast menus (e.g., Doom Eternal)
- ReShade overlays left visible for extended periods
- Any UI elements with bright/dark patterns that don't change
Mitigation
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Use odd “Frames Per Effect” values (3, 5, 7, etc.) - this naturally breaks the repetitive frame polarity pattern.
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Or keep LCD Safe Mode enabled - it’s on by default and introduces phase flips to prevent DC buildup. You may occasionally notice a very brief, single-frame flick, which is intentional and part of the burn-in protection cycle.
Note: This mitigation only applies to shader output — overlays rendered on top of the shader (like ReShade HUDs or GUI overlays) are outside its control and can still contribute to image retention.
LCD Safe Mode offers two selectable techniques:
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Phase Jump (default) - slowly accumulates small phase offsets and performs discrete phase jumps at long intervals. By default, the effect provides mild burn-in mitigation, but the Jump Rate can be increased to make the protection stronger, at the cost of slightly more noticeable phase flips.
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Frame Drop - skips a frame periodically to break the pattern.
These modes only activate when even-frame decay is used (e.g., 2 or 4 frames per effect), where phase repetition could otherwise accumulate charge.
Occasional flicker may occur with unstable frame rates or frame times. This is barely noticeable with proper V-Sync/G-Sync/FreeSync enabled.
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MIT License - See LICENSE file for details