Dead pixel test
Before I spend ten minutes cloning a speck out of a white background, I check that the speck is in the file and not in the monitor.
→ steps through the fields. H hides the bar.
Monitor, sensor or file?
| Test | If the dot… | It is |
|---|---|---|
| Scroll or pan the image | stays fixed on the glass | A monitor pixel or dirt on the screen |
| Scroll or pan the image | moves with the picture | In the file: sensor dust or a hot pixel |
| Compare several frames | sits in the same place in each | Sensor dust; clean the sensor |
| Wipe the screen | disappears | Dust |
Running the test
- Clean the screen with a dry microfibre cloth.
- On white, look for dark specks: dead pixels.
- On black, look for lit specks: stuck or hot pixels.
- On red, green and blue, look for a dot missing one colour.
Sensor dust shows best at small apertures against a plain white ground, which is exactly what we shoot. A quick test frame of a white screen at f/16, defocused, maps every speck on the sensor. More camera checks in calibrating a camera LCD.
Questions
One or two near the edge are a nuisance, not a fault in your photos. In the centre they are distracting enough to justify a return.
Pan the image. Dust moves with the picture; a monitor pixel stays put.
Sometimes, after hours of normal use. Dead ones rarely do.
Other bench tools
White Background Generator
PNG, JPG or WEBP at any size, plus a five-size batch for marketplaces.
Monitor Calibration
The near-white patches I use before I trust a screen with an edit.
Screen Resolution Checker
Real pixels and pixel ratio, so exports match the screen.
Screen Burn-In Test
Grey fields that show retained palettes and toolbars.
Refresh Rate Test
Checks the frame rate your tethering laptop actually runs.