Image processing

Multiple imaging modalities are used in cardiology for diagnostic purposes. Thus, familiarity and understanding of image processing is very important in the use and interpretation of the images produced by these modalities. The previous chapters examined signal processing concepts and techniques for time domain signals, which are considered one-dimensional signals where amplitude is plotted on the y-axis vs. time on the x-axis. In this chapter, we will explore images, which are two-dimensional signals where amplitude is plotted on the z-axis vs. space in the x- and y-axes. The amplitudes of a two-dimensional signal can be displayed in a three-dimensional plot, as seen in Fig. 9.1a. However, images are more commonly displayed as an intensity map where the colors of each point, known as a pixel, correspond to an amplitude value for that particular x and y value. Figure 9.1b shows the corresponding image of the three-dimension plot of Fig. 9.1a. The color of the image is scaled so that a z amplitude value of zero corresponds to black and one corresponds to white. The opposite of this scaling where black represents the highest amplitude values is also commonly seen. Different colors can also be used to represent different amplitude values.