Monitor Ghosting & Frame Skipping Test
Refresh rate = 1000 ÷ median frame gap in ms, so a 16.7 ms gap is 60 Hz and a 6.94 ms gap is 144 Hz. At the default 960 px/s the test object moves 16 px per frame at 60 Hz and 6.7 px at 144 Hz. Ghosting shows as a faded trail behind it; a skipped frame shows as a missing box in the frame grid when you photograph the screen with a long exposure.
How to use
- Press Full screen, set the room light low and keep the browser tab in front. The page measures your refresh rate first and uses it for everything below.
- Ghosting: watch the five rows. Each object moves at a different speed. Look for a faded trail or a colored fringe behind it, and note the fastest row where the object still has a clean edge. Try the gray, black and white backgrounds, because dark-to-light changes are where many panels smear.
- Frame skipping: switch to Frame skip. One box lights up per frame and the box number grows by one every frame. Take a photo of the screen with a shutter speed slower than one frame (see the notes) and look at the lit boxes. A gap in the run is a frame that never reached the screen.
- The numbers under the picture count frames the browser was late to draw. Press Reset to start a new count, for example after you change a setting.
How it works
The tool records the time of every requestAnimationFrame call. The refresh rate is 1000 divided by the median gap between calls in ms. The first 20 frames are thrown away as a warm-up.
A gap longer than 1.5 times the median counts as a dropped frame. Frames skipped = round(gap / median) - 1 for each such gap, and the percentage is frames skipped divided by all frames expected. Jitter is the standard deviation of the normal gaps.
Objects move by time, not by frame count: position = speed in px/s multiplied by elapsed seconds. Pixels per frame = speed / refresh rate, so 960 px/s is 16 px per frame at 60 Hz and 4 px per frame at 240 Hz.
What ghosting is
Ghosting is a trail that follows a moving object because pixels change color too slowly, or because the panel overshoots and adds a bright or dark halo. It is easiest to see on a gray background, where both dark and light transitions happen. Fast objects show it first.
| What you see | Likely cause | What to try |
|---|---|---|
| Smooth dark trail behind the object | Slow pixel response (common on VA and some IPS panels) | Raise the overdrive setting one step |
| Bright or colored halo ahead of the trail | Overdrive set too high (inverse ghosting) | Lower the overdrive setting |
| Whole object looks doubled | Low refresh rate or sample-and-hold blur | Raise the refresh rate in system settings |
| Trail only on one background | Panel is slow in only one transition | Compare the gray, black and white backgrounds |
How to photograph the frame skip grid
- Use a phone camera in pro or manual mode, or a camera with shutter priority. Set the shutter speed to about 1/10 s or 1/15 s, which is several frames long at 60 Hz or more.
- Hold the camera still, fill the frame with the grid and take a few shots. In each shot you should see an unbroken run of lit boxes.
- A dark box inside that run is a frame the screen did not show. A run that is a different length each time is normal, since the exposure start is random.
- Turn off any screen smoothing or motion interpolation first. It can fill in frames and hide skips.
What this test cannot see
- The counter only knows when the browser asked to draw. If the browser draws a frame but the GPU, cable or monitor drops it later, the counter stays at zero. The photo test catches that case, the counter does not.
- Background tabs, battery saver and a second monitor change the timing. Keep this tab in front on the screen you want to test.
- With variable refresh rate (G-Sync, FreeSync) the frame time is allowed to change, so the refresh rate shown can move.
- Ghosting is judged by eye. A reliable pixel response number needs a camera and a lab setup.
FAQ
What is a ghosting test?
It moves objects across the screen at several speeds so that trails or halos behind them become visible. If the object keeps a sharp edge at higher speeds, the panel keeps up. If a smear follows it, pixels are changing too slowly.
How do I test for frame skipping?
Open the Frame skip view, take a photo with a shutter speed of about 1/10 s and count the lit boxes. A gap in the run means a frame was not shown. The counter under the picture adds the frames the browser itself was late to draw.
Why does the counter show zero skipped frames when I see skips in the photo?
The counter works inside the browser. Frames lost after that point, in the graphics driver, the cable or the monitor, are invisible to it. The photo method sees the real screen.
What background should I use?
Start with gray. It exposes both dark and light transitions. Then check black, where slow dark pixels leave a purple or gray smear, and white.
Is a few dropped frames normal?
A few at the start are normal while the page and the system settle. Many drops every second point to a busy computer, power saving, a hidden tab or a browser problem.
Does it work on a phone or TV?
Yes, in any browser with full screen support. On iPhone the full screen button falls back to a page-filling view.