Truncate and Normalize image

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Is there a way to truncate and normalize an image in one step?

e.g. linearly map values from 50-100 to 0-255 ?

I can do it manually but of course its slow...

 byte range = (byte) (UpperThreshold - LowerThreshold);
            double f = (1.0 / (double) range) * 255;
            var copy = scan.Clone();
            for (int x = 0; x < copy.Cols; x++) {// todo this needs to be in native openCV to be fast enough for use
                for (int y = 0; y < copy.Rows; y++) {
                    byte v = copy.At<byte>(y, x);
                    double d = v;
                    d =  (d - LowerThreshold) * f;
                    if (d < 0) d = 0;
                    if (d > 255) d = 255;
                    v = (byte) d;
                    copy.Set<byte>(y,x,v);
                }
            }

            return copy;