To visualize an entire image stack in a single plane, use the Maximum intensity projection with light-on-dark images (e.g., fluorescence) or Minimum intensity projectionwith dark-on-light images (e.g., brightfield). See the Deep Focus method for an alternative.
Go to Image>View>Min (or Max) projection to display the projection instead of the original image.
The program identifies the maximum (or the minimum) intensity value of each pixel along the z axis is projected onto the 2D plane.