Within active matrix displays, such as LCDs, each pixel has its own individual transistor that controls its transmittance (see Figure 1). Occasionally, these individual transistors will short, or otherwise malfunction, resulting in a defective pixel. These are often visible as ‘bright’ pixels, which appear as single or several randomly-placed red, blue and/or green pixel elements on an all-black background. They can also appear as ‘missing’ or ‘dead’ pixels, black dots on all-white backgrounds. For many applications, such as LCD TV, digital cinema, and desktop monitors, the existence of defective pixels seriously degrades the image quality. In medical-imaging applications, defective pixels can even influence the critical decision-making process and therefore result in a wrong diagnosis. State-of-the art manufacturing processes are capable of producing displays with an average of no more than one faulty transistor in two million. With ever-increasing resolution, the number of defective pixels in displays increases accordingly. Typically, LCD panels are being inspected after manufacturing and panels that have too many defects are rejected. This results in a lower yield and higher panel cost. Recently, techniques have been described that make it possible to partially repair 3 defective pixels by transforming a very visible bright defect into a less visible dark defect. However, neither rejection nor partial repair is a true solution. We have been working on a completely different approach where we focus on making defective pixels invisible to the user by means of an image processing algorithm. Human observers perceive images by means of the eye, which is a complex lens system. Most lenses, including that in the human eye, are not perfect. As a result, when visual stimuli are passed through the cornea and lens, the stimuli undergo a certain degree of degradation or distortion. One typical degradation effect is the introduction of blur this means we do not perceive individual pixels, but a a low-pass-filtered combination of several neighboring pixels. Further, if one of those pixels is defective then it is possiFigure 1. An active matrix LCD works by blocking light that comes in from the back.
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