![]() ![]() (b) We can represent the intensity of a one-dimensional image using a simple graph that shows the light as a function of horizontal screen position. The image is brought to focus on the retina by the cornea and lens. (a) A one-dimensional monitor image consists of a set of lines at different intensities. We will use linear systems methods to develop a method of predicting the retinal image from any input image.įigure 2.2: Retinal image formation illustrated with a single-line input image. Since there is no hope of measuring the response to every possible input, to characterize optical blurring completely we must build a model that specifies how any input image is transformed into a retinal image. The image in Figure 2.2b shows one example of an infinite array of possible input images. Because the optics of the eye are not perfect, the retinal image is not an exact copy of the monitor image: The retinal image is a blurred copy of the input image. We will discuss the optical components of the visual system in more detail later in this chapter, but from simply looking at a picture of the eye in Figure 2.1 we can see that the monitor image passes through a lot of biological material before arriving at the retina. Hence, we can represent it using a curve as in Figure 2.2c. When the input image is one-dimensional, the retinal image will be one-dimensional, too. The output of the optical transformation is the image formed at the retina. The vertical graph in Figure 2.2b shows a measurement of the intensity of the monitor image at all screen locations. We can measure the intensity of the one-dimensional image by placing a light-sensitive device called a photodetector at different positions on the screen. We will call the pattern of light intensity we measure at the monitor screen the monitor image. One-dimensional patterns have a constant intensity along the, say, horizontal dimension and varies along the perpendicular (vertical) dimension. In this case the input is the light signal incident at the cornea. As an example, we will consider how simple one-dimensional intensity patterns displayed on a video display monitor are imaged onto the retina (Figure 2.2a). When we study transformations, we must specify their inputs and outputs. Since all of our visual experiences are influenced by this transformation, we begin the study of vision by analyzing the properties of image formation. ![]() The optical imaging of light incident at the cornea into an image at the retinal photoreceptors is the first visual transformation. The optic nerve fibers exit through a hole in the retina called the optic disk. The photoreceptor signals are communicated through the several layers of retinal neurons to the neurons whose output fibers makes up the optic nerve. The photoreceptors are part of a thin layer of neural tissue, called the retina. Light from a source arrives at the cornea and is focused by the cornea and lens onto the photoreceptors, a collection of light sensitive neurons. The bundle of output fibers is called the optic nerve.įigure 2.1 contains an overview of the imaging components of the eye. The retinal output fibers leave at a point in the retina called the blindspot. The fovea is a region of the retina that is specialized for high visual acuity and color perception. Light enters through the pupil which is bordered by the iris. The cornea and lens focus the image onto the retina. Because all of our visual experience is limited by the image formation within our eye, we begin by describing this transformation of the light signal and we will use this analysis as an introduction to linear methods.įigure 2.1: The imaging components of the eye. ![]() We can describe most of our understanding of these transformations, and thus most of our understanding of the early encoding of light by the visual pathways by using linear systems theory. The optic nerve representation is transformed into a cortical representation, and so forth. The photoreceptor responses are transformed to a neural response on the optic nerve. The retinal image is transformed into a neural response by the light sensitive elements of the eye, the photoreceptors. The initial encoding of light at the retina is but the first in a series of visual transformations: The stimulus incident at the cornea is transformed into an image at the retina. The cornea and lens bring light into focus at the light sensitive receptors in our retina and initiate a series of visual events that result in our visual experience. The cornea and lens are at the interface between the physical world of light and the neural encoding of the visual pathways. The Pointspread Function and Astigmatism.Implications of Homogeneity and Superposition. ![]()
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