Jernej LeticaPhotography Tools & Stories
Photography Calculators

Test a screen or a camera sensor for bad pixels

Fill the screen with solid colours to spot dead and stuck pixels, or load a dark frame to list the hot pixels of a camera sensor. Runs in your browser.

Built and written by Jernej Letica

Local browser processing · No upload · No account required

Screen test
  • Dead pixel: always black, on every colour.
  • Stuck pixel: always one colour, whatever the screen shows.
  • Hot pixel: a bright dot on a black screen.
Camera sensor hot pixels

How to test a screen for dead pixels

  1. Press Start full screen test. On an iPhone, where Safari has no full screen mode for a page, the test fills the whole window instead.
  2. Look at each colour in turn: black, white, red, green, blue, grey and a fine checkerboard. Tap, click, swipe or press the right arrow for the next one.
  3. Watch for a dot that stays black on every colour (dead), a dot that keeps one colour (stuck) or a bright dot on black (hot).
  4. If you find a stuck pixel, open the stuck pixel flasher, confirm the warning and drag the small square over it.

Dead, stuck and hot pixels

A dead pixel is a pixel that never lights up, so it is black on white, red, green and blue alike. A stuck pixel always shows one colour, because one or two of its three sub-pixels are stuck on. A hot pixel is a bright dot on a black screen. Clean the screen with a soft cloth first: a speck of dust looks like a dead pixel and wipes away.

Testing a phone or a monitor

The test is the same on a monitor, an iPhone and an Android phone. Turn the brightness to maximum, view the screen from straight on and take your time on each colour, because a single pixel is small. The fine checkerboard changes every pixel from one frame colour to the next, which also shows burn-in and uneven patches. A stuck pixel can sometimes be woken by the flasher, which cycles the pixel through red, green and blue fast. It is not a guaranteed fix, and a dead pixel does not come back.

Hot pixels on a camera sensor

On a camera sensor a hot pixel is one that records light that is not there, and it shows after a long exposure as a bright dot. To check, put the lens cap on, take a long exposure with the settings you use at night and load the JPEG or PNG here. The page compares each pixel with the median of its eight neighbours and lists the ones that are brighter by the chosen margin, with their x and y position and brightness, and circles them on a smaller preview. Everything is calculated in your browser and the frame is not uploaded.

The margin is 40 levels out of 255 by default, with 60 as strict and 20 as sensitive. A frame of uniform noise at 0 to 24 levels gives no result at the default, and five bright pixels planted on a near-black 4000 x 3000 frame are all found.

On the camera I use

I use a Sony A7 III, and I check it for hot pixels after long exposures, such as night skies and star trails. I shoot a dark frame with the lens cap on, in the same settings as the real photo, and load it here. A hot pixel that sits at the same x and y in two frames is the sensor; one that appears only once is noise.

Tips for better results

  • Test the screen in a dim room with the brightness at maximum.
  • Clean the screen first, so dust is not mistaken for a dead pixel.
  • Shoot the dark frame at the same ISO, shutter time and temperature as the photos you want to check.
  • Shoot two dark frames and compare: a pixel at the same x and y in both is a real hot pixel.
  • Use JPEG or PNG for the dark frame. A strongly compressed JPEG can smear one hot pixel over its neighbours; the list shows only the brightest of such a group.

Privacy

Your entered content never leaves your device. The screen test and the dark frame scan run locally in your browser, and the frame is not uploaded.

Frequently asked questions

What is a dead pixel test?

It fills the screen with solid colours, one after another, so that a pixel that does not behave stands out against a uniform background. A pixel that stays black is dead, one that keeps one colour is stuck, and a bright dot on black is hot.

How do I do a dead pixel test on an iPhone or Android phone?

Open this page and press Start full screen test. Android browsers can show the colours in full screen. iPhone Safari cannot, so the test fills the window instead; add the page to the Home Screen and open it from there to hide the browser bars. Tap for the next colour.

Can a dead pixel be fixed?

Not a dead one. A stuck pixel sometimes recovers when it is cycled through red, green and blue quickly, which is what the stuck pixel flasher does. Read the photosensitivity warning first and do not start it if flashing lights are a risk for you.

How does the camera sensor check find hot pixels?

It compares each pixel with the median of its eight neighbours and lists the pixels that are brighter by at least the chosen margin: 60 levels out of 255 for strict, 40 for normal and 20 for sensitive. For a dark frame the list is the hot pixels with their x, y and brightness.

Is my dark frame uploaded?

No. The image is read and scanned in your browser, and nothing is sent anywhere.

Related tools