The new BioImaging column of BioTechniques will feature short articles devoted to microscopy and digital imaging. The subject matter will address details of the methods used to produce images of cells and tissues at any magnification and resolution, and might include "tricks-of-the-trade", novel methods of specimen preparation, practices of image collection, tips on the digital manipulation and publication of images and historical perspectives. "The picture was taken with a digital camera" is

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... ard more and more often today. This article describes what a digital camera is, how it differs from a video camera and how to select one for your application. Digital vs. Analog Cameras When a charge-coupled device (CCD) camera incorporates an analog-to-digital (A/D) converter on the sensor or in close proximity, we call it a digital camera. Since CCD chips, like all optical sensors, are analog devices that produce a stream of varying voltages, the term digital is used only when those voltages are digitized in the camera and output in a computercompatible format. In a 12-bit digital camera, the analog signal from the CCD is digitized with 12-bit depth by the on-board A/D converter. Whether or not the output can actually be resolved into 4096 (2 12 or 12 bits) discrete intensity levels depends on the camera noise. To discriminate between individual intensity levels, each gray level step should be about 2.7 times larger than the camera noise. Otherwise, the difference between steps 2982 and 2983, for example, cannot be resolved with certainty (for additional information, see Chapter 12 in Reference 1). Some so-called 12-bit cameras have so much camera noise that 4096 discrete steps cannot be discriminated. The sources and magnitudes of camera noise will be considered below. Why Digital?