ABSTRACT
Image-based assays consist of the analysis of digital images of fluorescently labeled cells taken with a optical magnification system. This analysis is performed by a variety of commercially available image processing programs and is colloquially referred to as “image processing” or “image analysis.” Digital images are composed of pixels or squares of uniform gray values. These gray values commonly range from 0 (pure black) to 4095 (pure white) in the case of 12-bit digital cameras, and are sometimes referred to as intensity levels or values. Image analysis measures patterns of pixel gray values (two-dimensional arrangement of intensity values) contained in digital images. This analysis yields a large amount of unique information about the objects contained in the digital image. For example, changes in cell shape can provide information about toxicity or cell death, and the location of a particular protein within subcellular compartments can provide information about that protein’s activity level (Figure 29.1).
