Twenty years after the transition from bulky CRT monitors to sleeker LCDs, display technology experts are still striving to recapture a lost quality: the motion clarity of cathode ray tube displays. While modern monitors have vastly improved since the smeary, washed-out LCDs of the mid-2000s, even the best high-refresh-rate displays are still chasing the ghost-free precision of their predecessors.
Mark Rejhon, founder of Blur Busters, explains that while older individuals remember the motion clarity of CRTs, younger generations may not. Modern LCDs were particularly poor in this regard, with slow pixel response times creating noticeable "ghost" trails on fast-moving images. Even an expensive early HD display, which seemed state-of-the-art at the time, now reveals its shortcomings compared to the richer colors and smoother motion of a CRT.
Cathode Ray 'Tude
This pursuit of CRT-like clarity is driving innovation in display technology. Nvidia's G-Sync Pulsar, integrated into gaming monitors this year, utilizes backlight strobing and a rolling refresh cycle akin to CRTs to achieve a perceived clarity of 1,000 Hz. This technology, however, is exclusive to Nvidia GPUs and not yet available on OLED panels.
In late 2024, Rejhon and former Nvidia developer Timothy Lottes introduced a breakthrough algorithm for simulating CRT tubes. This software leverages displays with refresh rates of 240 Hz and above to drastically reduce motion blur, particularly for content locked at 60 Hz. The technique aims to recreate the "phosphor fade" of CRTs, which is less taxing on the eyes than traditional black frame insertion (BFI) methods.
"The two main ways to reduce display motion blur is either flicker the frames (like a CRT) or add more frame rate (for high Hz)," Rejhon stated. "Both methods will show frames more briefly, like a fast camera shutter, and result in less display motion blur. CRTs could flicker pixels brightly for less than 1/1000 second. The bonus with CRT is you do not require more frame rate to achieve low motion blur."
The effect is akin to temporal upscaling, allowing content at 60 frames per second to appear as smooth as content running at significantly higher frame rates. The Asus ROG Swift OLED PG27AQWP-W, with its 540 Hz refresh rate (and 720 Hz at 720p resolution), is an ideal monitor for testing this technology. OLED panels offer true blacks and high brightness, mimicking the contrast of CRTs, while high refresh rates help simulate the electron beam drawing the image.
Rejhon further noted that CRT simulation is gentler on the eyes than BFI because it utilizes phosphor fade and rolling scan, ensuring some light is always emitted on the screen. However, implementing this technology is complex. The first iteration was a shader for Retroarch, followed by integration into ShaderGlass and then a separate tool called ShaderBeam, developed by Mausimus. ShaderBeam is currently the most effective way to utilize Rejhon's algorithm.
Shader Dreams
ShaderBeam operates by capturing screen content and applying the CRT simulation as an overlay. According to Mausimus, its effectiveness hinges on perfect synchronization with both the display and the input content, which is challenging due to the limitations of current operating systems and GPU drivers. Achieving optimal results often requires disabling features like VRR, adjusting graphics card driver settings, using tools like Process Lasso to prioritize ShaderBeam, and potentially even dedicating a secondary GPU for the simulation to avoid desync issues.
The effort required for ShaderBeam is substantial, involving complex troubleshooting to avoid issues like flashing, stuttering, and color banding. However, when successfully implemented, the visual improvement is remarkable. Details that would normally blur become sharply defined, as seen in games like Metroid Prime 2, Quake, and Factorio. Mausimus highlighted that with the shader, players can still discern fine details in textures even during rapid scene movement.
Future Vision
While ShaderBeam offers a glimpse into the potential of CRT simulation, its current implementation requires significant tinkering and compromises. Experts suggest that true nirvana will likely come from advancements in hardware, such as next-generation Nvidia Pulsar monitors, or from OS-level support from Microsoft. Mausimus hopes that tools like ShaderBeam will spur manufacturers to properly support this technology.
Rejhon anticipates that built-in shader hooks in operating systems and future display technologies will make CRT simulation more user-friendly. This is part of an ongoing advocacy effort by Blur Busters' Open Source Display Shaders Initiative. The pursuit of CRT clarity demonstrates a desire to recapture a lost visual quality, suggesting that the path forward for display technology may, in some ways, lead back to the past.