naïve attempt at lab transform prior to normalization

resize.cc

   // Apply normalization
    if (baton->normalize) {
      // normalize the luminance band in LAB space:
      VipsImage *lab;
      if (vips_colourspace(image, &lab, VIPS_INTERPRETATION_LAB, NULL)) {
        return Error();
      }
      vips_object_local(hook, lab);

      VipsImage *luminance;
      if (vips_extract_band(lab, &luminance, 0, "n", 1, NULL)) {
        return Error();
      }
      vips_object_local(hook, luminance);

      VipsImage *chroma;
      if (vips_extract_band(lab, &chroma, 1, "n", 2, NULL)) {
        return Error();
      }
      vips_object_local(hook, chroma);

      VipsImage *stats;
      if (vips_stats(luminance, &stats, NULL)) {
        return Error();
      }
      vips_object_local(hook, stats);
      double min = *VIPS_MATRIX(stats, 0, 0);
      double max = *VIPS_MATRIX(stats, 1, 0);
      double f = 100.0 / (max - min);
      double a = -(min * f) + 0.5;

      VipsImage *luminance100;
      if (vips_linear1(luminance, &luminance100, f, a, NULL)) {
        return Error();
      }
      vips_object_local(hook, luminance100);

      VipsImage *normalized;
      if (vips_bandjoin2(luminance100, chroma, &normalized, NULL)) {
        return Error();
      }
      vips_object_local(hook, normalized);

      image = normalized;
    }