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Iridix is unique because it automatically generates a specific tone curve for every pixel in the image. Some parts of the image can be made much brighter, while other parts can be kept the same or even made darker. In the examples shown on this slide, the curve which is applied to the pixel in the middle of the red circle is shown. The curve was generated automatically by analyzing the image in a region around the pixel, approximately covering the area of the circle. The size of the area can be changed by parameter control. Iridix is a technique in the class “space-varying dynamic range compression algorithms” which is related to local histogram modification, but is more sophisticated. It analyzes the image in different regions, but these regions are not blocks (like in MPEG compression). The processing is done in frequency space (like DCT) so that there are no sharp edges between regions, and therefore no block-type effects are created. Iridix works through a two-pass process. In the first pass, the image is analyzed and a type of histogram is created. Unlike the normal histogram, this is a multi-dimensional histogram with axes of luminance, color, and pixel x- and y- coordinates. This histogram is then used to calculate the curves for each pixel. In the second pass, the curves are applied to the image and the result is generated. Although this is a complex mathematical procedure, Apical (acquired by Arm®) has worked to create a very efficient hardware implementation which fits optimally into Intel® Cyclone® FPGAs.
