Dead Pixel Tester

A dead pixel is a point on your monitor that no longer lights up, so it shows as a tiny dark dot, most visible against a white or bright background. On the screen you edit on, a dead or stuck pixel can look like dust or a blemish in your photo, and you may waste time trying to retouch a flaw that is not in the file at all. Knowing where the defects sit on your display lets you ignore them while editing and decide whether the monitor needs a warranty claim.

Clean your screen first so dust is not mistaken for a defect. Click Start Fullscreen, or anywhere in the box labeled Click Here to Begin Test, and the page switches to full screen showing solid black. Click the screen or press the Right or Up arrow, Space or Enter to move to the next color, and the Left or Down arrow to go back. Look over the whole display on each color from a normal viewing distance. Press Esc to leave the test.

Pixels can fail as a display ages, and a single dark or bright dot is easy to miss in day-to-day use until it lands in the middle of a client's face while you retouch. A quick check every few months, and whenever you notice a spot that stays in the same place on screen as you move through different photos, tells you whether the problem is your display or your files. It takes a minute and needs nothing but a clean screen.

Run it as soon as you unpack a new or used monitor or laptop, while you are still inside the seller's return window, since manufacturers set their own rules on how many defective pixels qualify for a replacement. It is also worth testing before a busy season, before calibrating a display for color-critical work, and any time you see a fixed dot that does not move when you pan or zoom an image. Let the screen warm up for a few minutes first.

A dead pixel on a monitor stays dark, so it shows up most clearly on the white screen. A stuck pixel has one or more of its red, green or blue subpixels fixed on or off, so it shows as a colored dot, easiest to see on the black screen or on a color it does not match. A hot pixel is a camera sensor effect: a bright speck that appears in long or high ISO exposures as the sensor warms. This tester checks your display, so it finds dead and stuck screen pixels, not hot pixels in your camera.

If a spot appears in your photos but not on any of the solid test colors, the problem is in the files, not your screen. Check whether it sits in the same place across several images from the same camera. Soft, blurry spots that become more defined at narrow apertures such as f/16 are usually sensor dust, which a sensor cleaning removes. Sharp single-pixel dots in the same position are more likely hot or stuck pixels on the camera sensor, which this monitor test cannot detect.

No. The Dead Pixel Tester only checks the screen you are viewing it on. It does not open or analyze photos, so it cannot find defects in a camera sensor. To check a sensor, a common method is to shoot a frame with the lens cap on at your base ISO and an exposure of a few seconds, then view it at 100 percent in your editing software and look for bright dots that appear in the same place in every frame.

A truly dead monitor pixel usually cannot be repaired at home. Note its position and the color it shows, then check your monitor's warranty, since many manufacturers will replace a display once the number or position of defective pixels meets their policy. A stuck pixel sometimes recovers on its own after the display has been in use for a while. If the defect stays and falls within the warranty terms, contact the manufacturer or seller with a photo of the screen showing the dot.

The test cycles through seven full-screen colors: black, white, red, green, blue, yellow and cyan. On black, look for any dot that glows, which points to a stuck pixel. On white, look for dark dots, which are usually dead pixels. The red, green and blue screens show whether a single subpixel is stuck on or off, and yellow and cyan add two mixed colors as a cross-check. The on-screen instructions fade after three seconds so they do not hide part of the display.

High ISO settings and long exposures make the camera sensor work harder and run warmer, and heat increases electrical leakage in individual photosites. The result is hot pixels: bright, colored specks scattered across dark areas of the frame. Unlike dead monitor pixels, hot pixels come and go with temperature and exposure time, and they are recorded into the photo itself. Many cameras offer long exposure noise reduction to subtract them. This tester checks your monitor, so use it to rule out the screen before blaming the sensor.