Tackling Motion Artifacts in Industrial LCDs: A Deep Dive into Hold-Type vs. Impulse-Type Displays

In high-stakes industrial environments, from robotic arm controls to high-speed visual inspection systems, motion clarity on a display is not a luxury—it’s a necessity. An operator misinterpreting a blurred image on an HMI could lead to production errors, equipment damage, or safety hazards. This is why understanding and mitigating motion artifacts, the visual distortions that occur with moving images, is a critical task for any engineer or system designer selecting an industrial display. At the core of this issue lies a fundamental difference in how displays render images: the “Hold-Type” method, common in all modern LCDs and OLEDs, versus the “Impulse-Type” method, characteristic of older CRT displays.

1. The Root Cause: Why We Perceive Motion Blur on Modern Displays

It may seem counterintuitive, but much of the motion blur we see on an LCD screen isn’t solely caused by slow pixel transitions (though that is a factor). The primary culprit is a phenomenon rooted in the interaction between our own visual system and the “sample-and-hold” nature of modern displays. Here’s the breakdown:

• Smooth Pursuit Eye Movement: When tracking a moving object, like a dot traversing a screen, our eyes don’t jump from point to point. Instead, they move in a smooth, continuous motion to keep the object focused on the retina.
• Sample-and-Hold Mechanism: A standard LCD is a “hold-type” display. This means that once a frame is drawn, each pixel “holds” its color and brightness state for the entire duration of that frame (e.g., for 16.7 milliseconds on a 60Hz display) until the next frame instantly replaces it.

The conflict arises because your eye is moving smoothly across the screen, while the image itself is presented as a series of static steps. As your eye tracks the moving object, the static, held frame is effectively “smeared” across your retina, creating the perception of motion blur. This happens even if the pixels change color instantaneously (0ms response time). Think of it like a flipbook where each page is held in view for a moment before the next one appears, instead of being shown in a rapid, fleeting flash.

2. Hold-Type vs. Impulse-Type Displays: A Technical Comparison

To grasp the solution, we must first clearly define the two fundamental display driving methods. The distinction lies in how long a pixel is illuminated during each refresh cycle.

Hold-Type Displays (e.g., LCD, OLED)

As described above, nearly all modern flat-panel displays, including every industrial TFT-LCD and OLED panel, are sample-and-hold displays. An image is presented and held continuously, accounting for nearly 100% of the frame’s duration. While this produces a stable, flicker-free image, it is the direct cause of eye-tracking-based motion blur.

An important metric here is Motion Picture Response Time (MPRT), which measures how long a pixel is visibly lit. For a standard 60Hz hold-type display, the MPRT is approximately the full frame duration of 16.7ms. This is different from the more commonly advertised Grey-to-Grey (GtG) response time, which only measures how quickly a pixel can change color. A display can have a very fast 1ms GtG but still exhibit significant motion blur due to a high MPRT.

Impulse-Type Displays (e.g., CRT, DLP, Strobed Backlights)

Impulse-type displays work differently. They flash the image on the screen for only a very brief portion of the frame time, followed by a period of darkness. Classic Cathode Ray Tube (CRT) monitors were a perfect example; their phosphors would light up when struck by an electron beam and then quickly fade. This short burst of light, or “impulse,” followed by darkness, breaks the continuous smearing effect on our retinas. Your eye sees the object at a distinct point in space and time, then moves during the dark period, and sees the next updated frame at its new position. This closely mimics how we perceive motion in the real world and results in exceptionally clear moving images.

Core Differences Summarized

The following table outlines the key engineering trade-offs between these two display technologies:

Characteristic	Hold-Type Display (Standard LCD/OLED)	Impulse-Type Display (CRT / Strobed LCD)
Motion Blur	High (due to sample-and-hold persistence)	Very Low
Flicker	Inherently flicker-free	Noticeable flicker, especially at lower refresh rates
Brightness	High and consistent	Significantly lower (backlight/pixel is off for a large portion of the time)
Visual Mechanism	Image is continuously displayed (“held”) for the full frame time	Image is briefly flashed (“impulsed”) with dark periods in between
Core Metric	MPRT is approximately equal to the frame duration (e.g., 16.7ms @ 60Hz)	MPRT is determined by the impulse duration (e.g., 1-4ms)
Complexity/Cost	Standard for all modern panels	Requires specialized backlight control or panel technology

3. Practical Solutions: Making Hold-Type Displays Behave Like Impulse-Type

Since CRTs are no longer a viable option and nearly all industrial panels are hold-type LCDs, engineers have developed clever techniques to mimic the behavior of impulse-type displays. These methods focus on reducing the MPRT by shortening the time a frame is visible to the eye.

Technique 1: Black Frame Insertion (BFI)

Black Frame Insertion is the most direct way to simulate an impulse-driven display. The display controller inserts a completely black frame between each frame of actual image data. For example, on a 120Hz display showing 60fps content, the sequence would be: Image Frame 1 -> Black Frame -> Image Frame 2 -> Black Frame, and so on. This effectively cuts the visibility time of each image frame in half, drastically reducing motion blur.

• Pros: Highly effective at reducing motion blur without requiring complex hardware.
• Cons: It cuts perceived brightness by 50% or more, which can be unacceptable in brightly lit industrial environments. It can also introduce visible flicker, especially if the resulting frame rate is low (e.g., 60Hz source with BFI results in a 30Hz flicker effect).

Technique 2: Backlight Strobing / Scanning

A more sophisticated and common approach is backlight strobing, known by various marketing names like ULMB, DyAc, or simply Motion Blur Reduction. Instead of inserting a black data frame, this technique rapidly switches the LED backlight off and on in sync with the refresh rate. The backlight is turned off while the liquid crystals are transitioning to the next frame (the slow GtG part) and is then strobed on for a very short period only when the frame is fully rendered.

This method cleverly hides the pixel transitions and presents a brief, sharp impulse of light to the user, just like a CRT. More advanced “scanning backlights” strobe different horizontal sections of the backlight in sequence, further refining the effect and reducing artifacts.

• Pros: Excellent motion blur reduction, often with adjustable pulse widths to trade off clarity for brightness. Bypasses much of the limitation imposed by GtG response time.
• Cons: Still causes a significant drop in brightness. Can introduce artifacts like “strobe crosstalk” (a faint double-image effect) if the strobing is not perfectly timed with the LCD panel’s response. Cannot typically be used simultaneously with Variable Refresh Rate (VRR) technologies like FreeSync or G-SYNC.

The Role of Overdrive

It’s also important to mention Overdrive (often called “Trace Free” or “AMA”). This technique applies a temporary, higher voltage to the liquid crystals to make them twist into position faster, thus improving the GtG response time. While overdrive is essential for fast-refresh LCDs and a prerequisite for clean backlight strobing, it does not, by itself, solve the sample-and-hold motion blur problem. It only reduces the “ghosting” artifact that comes from slow pixel transitions, not the primary blur that comes from eye-tracking. Getting the overdrive settings right is a balancing act; too little and you get ghosting, too much and you get “inverse ghosting” or coronas.

4. Application Guidance and Future Outlook

For an engineer specifying an industrial HMI or machine vision display, motion clarity is paramount. When evaluating displays, it’s crucial to look beyond GtG response time and understand the display’s capabilities for reducing motion blur.

Engineer’s Checklist for Motion Clarity:

• Is the application motion-critical? For static readouts, motion blur is irrelevant. For high-speed inspection, robotics, or vehicle displays, it is a primary concern.
• Check for Motion Blur Reduction Features: Does the display datasheet or manufacturer documentation mention backlight strobing, BFI, or a specific “1ms MPRT” mode? This is a key indicator of its suitability for motion-critical tasks. A display with a fast GtG time is a good start, but true clarity comes from reducing MPRT. For a deeper look at this metric, explore our guide on achieving motion clarity and LCD response time.
• Consider Environmental Brightness: All impulse-based techniques reduce brightness. Ensure the display’s maximum brightness in its strobed mode is sufficient for the intended operating environment.
• Evaluate Artifacts: If possible, test the display in its motion blur reduction mode. Look for strobe crosstalk or excessive flicker that could be more distracting than the original blur. High-quality automated quality control in manufacturing can help minimize these issues.

Looking forward, technologies like MicroLED offer a potential long-term solution. As a self-emissive technology, each pixel can be controlled individually, allowing it to operate as either a hold-type or a true impulse-type display without the need for a separate backlight, potentially offering the best of both worlds. However, for the foreseeable future, mastering the application of backlight strobing and BFI on high-refresh-rate IPS and VA industrial LCDs remains the most practical and effective strategy for conquering motion artifacts.