Add support to normalise for lower and upper percentiles (#3583)

src/operations.cc

@@ -6,7 +6,6 @@
 #include <memory>
 #include <tuple>
 #include <vector>
-
 #include <vips/vips8>
 
 #include "common.h"
@@ -46,7 +45,7 @@ namespace sharp {
   /*
    * Stretch luminance to cover full dynamic range.
    */
-  VImage Normalise(VImage image) {
+  VImage Normalise(VImage image, int const lower, int const upper) {
     // Get original colourspace
     VipsInterpretation typeBeforeNormalize = image.interpretation();
     if (typeBeforeNormalize == VIPS_INTERPRETATION_RGB) {
@@ -56,9 +55,11 @@ namespace sharp {
     VImage lab = image.colourspace(VIPS_INTERPRETATION_LAB);
     // Extract luminance
     VImage luminance = lab[0];
+
     // Find luminance range
-    int const min = luminance.percent(1);
-    int const max = luminance.percent(99);
+    int const min = lower == 0 ? luminance.min() : luminance.percent(lower);
+    int const max = upper == 100 ? luminance.max() : luminance.percent(upper);
+
     if (std::abs(max - min) > 1) {
       // Extract chroma
       VImage chroma = lab.extract_band(1, VImage::option()->set("n", 2));

src/operations.h

@@ -22,7 +22,7 @@ namespace sharp {
   /*
    * Stretch luminance to cover full dynamic range.
    */
-  VImage Normalise(VImage image);
+  VImage Normalise(VImage image, int const lower, int const upper);
 
   /*
    * Contrast limiting adapative histogram equalization (CLAHE)

src/pipeline.cc

@@ -74,6 +74,7 @@ class PipelineWorker : public Napi::AsyncWorker {
       VipsAngle autoRotation = VIPS_ANGLE_D0;
       bool autoFlip = FALSE;
       bool autoFlop = FALSE;
+
       if (baton->useExifOrientation) {
         // Rotate and flip image according to Exif orientation
         std::tie(autoRotation, autoFlip, autoFlop) = CalculateExifRotationAndFlip(sharp::ExifOrientation(image));
@@ -682,7 +683,7 @@ class PipelineWorker : public Napi::AsyncWorker {
 
       // Apply normalisation - stretch luminance to cover full dynamic range
       if (baton->normalise) {
-        image = sharp::Normalise(image);
+        image = sharp::Normalise(image,  baton->normaliseLower, baton->normaliseUpper);
       }
 
       // Apply contrast limiting adaptive histogram equalization (CLAHE)
@@ -1483,6 +1484,8 @@ Napi::Value pipeline(const Napi::CallbackInfo& info) {
   baton->linearB = sharp::AttrAsVectorOfDouble(options, "linearB");
   baton->greyscale = sharp::AttrAsBool(options, "greyscale");
   baton->normalise = sharp::AttrAsBool(options, "normalise");
+  baton->normaliseLower = sharp::AttrAsUint32(options, "normaliseLower");
+  baton->normaliseUpper = sharp::AttrAsUint32(options, "normaliseUpper");
   baton->tintA = sharp::AttrAsDouble(options, "tintA");
   baton->tintB = sharp::AttrAsDouble(options, "tintB");
   baton->claheWidth = sharp::AttrAsUint32(options, "claheWidth");

src/pipeline.h

@@ -99,6 +99,8 @@ struct PipelineBaton {
   double gammaOut;
   bool greyscale;
   bool normalise;
+  int normaliseLower;
+  int normaliseUpper;
   int claheWidth;
   int claheHeight;
   int claheMaxSlope;
@@ -262,6 +264,8 @@ struct PipelineBaton {
     gamma(0.0),
     greyscale(false),
     normalise(false),
+    normaliseLower(1),
+    normaliseUpper(99),
     claheWidth(0),
     claheHeight(0),
     claheMaxSlope(3),