/// ImageBufAlgo::contrast ---------------------------------------------------
/// Formula:          out = (in-pivot)*contrast + pivot
///
/// Parameters:
/// R               - Output image R must have float pixel data type. R can be
///                   initialized by the caller or not. If initialized and
///                   R.nchannels() != A.nchannels(), then false is returned.
///                   If not initialized, then it is initialized from A's spec
///                   but the format is set to float, since output images from
///                   IBA functions have float pixel data type by convention.
/// A               - Input image A must have float pixel data type and at
///                   least one channel.
/// contrast        - A float parameter that can take values >= 0. Values < 0
///                   are not allowed because the image colors get inverted.
///                   Values closer to 0 result in values closer to pivot
///                   and values further than 0 result in values further than
///                   pivot. Values above 1 result in very strong contrast.
/// pivot           - A float parameter that must be in range 0->1. All
///                   pixel values deviate from this pivot value to lesser
///                   or greater degree. Values closer to pivot deviate
///                   less, and values further deviate to bigger degree. This
///                   is the case because contrast adjustment essentially is
///                   a multiplication.
/// roi             - The operation will be applied only to this region. If
///                   roi is not defined, then it is initialized from R.
///                   If it is defined but not fully contained in R's region,
///                   then its new value is the intersection region with R.
/// threads         - Number of threads.
/// --------------------------------------------------------------------------
bool DLLPUBLIC contrast (ImageBuf &R, const ImageBuf &A,
                         float contrast, float pivot,
                         ROI roi = ROI(), int threads = 0);

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