Count cells from a phone photo of the chamber.

• One full 1 mm square, with all four corners, inside the frame. The rulings are what the scale is measured from, so the count needs the whole square, not most of it.
• Rulings crisp. If the lines are soft the cells are softer, and a blurred cell is a missed cell or a wrong live-or-dead call.
• Full resolution, no zoom. Frames under about 2,000 pixels on the short side are too small to count reliably, and digital zoom throws pixels away. A modern phone’s main camera clears this easily; a front camera or an old phone may not.
• Even light. The background bright but not white, detail kept in the blue cells. Blown highlights erase dead cells and crushed shadows erase live ones.
• JPEG, PNG, TIFF. HEIC and HEIF photos are converted to JPEG in the browser on Safari and iOS, the only browsers that can decode them; elsewhere, export the photo as JPEG first. Nothing is resized on the way in.

1. 1

   Set the microscope first

   Use the 10x objective, bring the rulings into sharp focus and set the light so the background is bright but not white and the blue cells keep their colour. What you see in the eyepiece is what the phone gets.

2. 2

   Hold the phone to the eyepiece

   Put the phone’s main camera lens flat against the eyepiece and centre it until the round field fills the screen. Rest your hands on the microscope. Tap the grid on the screen so the phone focuses and exposes on the rulings.

3. 3

   Frame one full square

   Move the stage until one full 1 mm square, with all four corners, sits inside the field. Do not zoom: digital zoom throws away the pixels the count needs. Take the photo at the camera’s full resolution.

4. 4

   Upload the photo

   Open CellCount on the phone itself, or send the photo to the laptop, and drop it on the counting page. CellCount measures the rulings in the photo, counts inside the square and applies the protocol’s dilution and sensitivity. HEIC photos are converted in the browser on Safari and iOS; elsewhere, export the photo as JPEG first.

5. 5

   Check the marks and accept

   Every detected cell is drawn on your photo. Add, delete or flip the ones you disagree with, then accept the count. The concentration, the viability and the size histogram come with it, and so does the record of who accepted it and when.

A check on a number you doubt, a second reading of a chamber somebody else counted, a count at a bench with no camera, a teaching lab, a field site. For cells of about ten micrometres and larger, which covers most mammalian cell lines and primary cells, a phone photo that meets the list above counts well. Smaller cells such as yeast want the resolution of a camera on the microscope port, and so does the daily bench count: the camera frames the same square at the same scale every time, counts live into the browser and never needs a steady hand.

The same protocol runs on a phone photo, a camera frame and a counter’s exported image, so a phone count from Tuesday and a camera count from Wednesday were made the same way and can be compared. The recommended setup is described on the About page.

Every detected cell marked on your photo, live and dead in their own colours; the count, the concentration in cells per mL from the measured grid and your dilution, the viability, and a cell-size histogram with the gate you set. The count is accepted by a named person, dated, sealed with a hash, and leaves as a results document or an export bundle with the image, its overlay and the results as CSV.