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

lib/constructor.js

@@ -235,6 +235,8 @@ const Sharp = function (input, options) {
     gammaOut: 0,
     greyscale: false,
     normalise: false,
+    normaliseLower: 1,
+    normaliseUpper: 99,
     claheWidth: 0,
     claheHeight: 0,
     claheMaxSlope: 3,

lib/index.d.ts

@@ -447,18 +447,26 @@ declare namespace sharp {
         negate(negate?: boolean | NegateOptions): Sharp;
 
         /**
-         * Enhance output image contrast by stretching its luminance to cover the full dynamic range.
-         * @param normalise true to enable and false to disable (defaults to true)
+         * Enhance output image contrast by stretching its luminance to cover a full dynamic range.
+         *
+         * Uses a histogram-based approach, taking a default range of 1% to 99% to reduce sensitivity to noise at the extremes.
+         *
+         * Luminance values below the `lower` percentile will be underexposed by clipping to zero.
+         * Luminance values above the `upper` percentile will be overexposed by clipping to the max pixel value.
+         *
+         * @param normalise options
+         * @throws {Error} Invalid parameters
          * @returns A sharp instance that can be used to chain operations
          */
-        normalise(normalise?: boolean): Sharp;
+        normalise(normalise?: NormaliseOptions): Sharp;
 
         /**
          * Alternative spelling of normalise.
-         * @param normalize true to enable and false to disable (defaults to true)
+         * @param normalize options
+         * @throws {Error} Invalid parameters
          * @returns A sharp instance that can be used to chain operations
          */
-        normalize(normalize?: boolean): Sharp;
+        normalize(normalize?: NormaliseOptions): Sharp;
 
         /**
          * Perform contrast limiting adaptive histogram equalization (CLAHE)
@@ -1218,6 +1226,13 @@ declare namespace sharp {
         alpha?: boolean | undefined;
     }
 
+    interface NormaliseOptions {
+      /** Percentile below which luminance values will be underexposed. */
+      lower?: number | undefined;
+      /** Percentile above which luminance values will be overexposed. */
+      upper?: number | undefined;
+    }
+
     interface ResizeOptions {
         /** Alternative means of specifying width. If both are present this takes priority. */
         width?: number | undefined;

lib/operation.js

@@ -469,16 +469,50 @@ function negate (options) {
 }
 
 /**
- * Enhance output image contrast by stretching its luminance to cover the full dynamic range.
+ * Enhance output image contrast by stretching its luminance to cover a full dynamic range.
+ *
+ * Uses a histogram-based approach, taking a default range of 1% to 99% to reduce sensitivity to noise at the extremes.
+ *
+ * Luminance values below the `lower` percentile will be underexposed by clipping to zero.
+ * Luminance values above the `upper` percentile will be overexposed by clipping to the max pixel value.
  *
  * @example
- * const output = await sharp(input).normalise().toBuffer();
+ * const output = await sharp(input)
+ *   .normalise()
+ *   .toBuffer();
  *
- * @param {Boolean} [normalise=true]
+ * @example
+ * const output = await sharp(input)
+ *   .normalise({ lower: 0, upper: 100 })
+ *   .toBuffer();
+ *
+ * @param {Object} [options]
+ * @param {number} [options.lower=1] - Percentile below which luminance values will be underexposed.
+ * @param {number} [options.upper=99] - Percentile above which luminance values will be overexposed.
  * @returns {Sharp}
  */
-function normalise (normalise) {
-  this.options.normalise = is.bool(normalise) ? normalise : true;
+function normalise (options) {
+  if (is.plainObject(options)) {
+    if (is.defined(options.lower)) {
+      if (is.number(options.lower) && is.inRange(options.lower, 0, 99)) {
+        this.options.normaliseLower = options.lower;
+      } else {
+        throw is.invalidParameterError('lower', 'number between 0 and 99', options.lower);
+      }
+    }
+    if (is.defined(options.upper)) {
+      if (is.number(options.upper) && is.inRange(options.upper, 1, 100)) {
+        this.options.normaliseUpper = options.upper;
+      } else {
+        throw is.invalidParameterError('upper', 'number between 1 and 100', options.upper);
+      }
+    }
+  }
+  if (this.options.normaliseLower >= this.options.normaliseUpper) {
+    throw is.invalidParameterError('range', 'lower to be less than upper',
+      `${this.options.normaliseLower} >= ${this.options.normaliseUpper}`);
+  }
+  this.options.normalise = true;
   return this;
 }
 
@@ -486,13 +520,17 @@ function normalise (normalise) {
  * Alternative spelling of normalise.
  *
  * @example
- * const output = await sharp(input).normalize().toBuffer();
+ * const output = await sharp(input)
+ *   .normalize()
+ *   .toBuffer();
  *
- * @param {Boolean} [normalize=true]
+ * @param {Object} [options]
+ * @param {number} [options.lower=1] - Percentile below which luminance values will be underexposed.
+ * @param {number} [options.upper=99] - Percentile above which luminance values will be overexposed.
  * @returns {Sharp}
  */
-function normalize (normalize) {
-  return this.normalise(normalize);
+function normalize (options) {
+  return this.normalise(options);
 }
 
 /**

package.json

@@ -85,7 +85,8 @@
     "Brodan <christopher.hranj@gmail.com",
     "Ankur Parihar <ankur.github@gmail.com>",
     "Brahim Ait elhaj <brahima@gmail.com>",
-    "Mart Jansink <m.jansink@gmail.com>"
+    "Mart Jansink <m.jansink@gmail.com>",
+    "Lachlan Newman <lachnewman007@gmail.com>"
   ],
   "scripts": {
     "install": "(node install/libvips && node install/dll-copy && prebuild-install) || (node install/can-compile && node-gyp rebuild && node install/dll-copy)",

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),

test/unit/normalize.js

@@ -34,7 +34,7 @@ describe('Normalization', function () {
   it('spreads grayscaled image values between 0 and 255', function (done) {
     sharp(fixtures.inputJpgWithLowContrast)
       .greyscale()
-      .normalize(true)
+      .normalize()
       .raw()
       .toBuffer(function (err, data, info) {
         if (err) throw err;
@@ -107,4 +107,58 @@ describe('Normalization', function () {
         done();
       });
   });
+
+  it('should handle luminance range', function (done) {
+    sharp(fixtures.inputJpgWithLowContrast)
+      .normalise({ lower: 10, upper: 70 })
+      .raw()
+      .toBuffer(function (err, data, info) {
+        if (err) throw err;
+        assertNormalized(data);
+        done();
+      });
+  });
+
+  it('should allow lower without upper', function () {
+    assert.doesNotThrow(() => sharp().normalize({ lower: 2 }));
+  });
+  it('should allow upper without lower', function () {
+    assert.doesNotThrow(() => sharp().normalize({ upper: 98 }));
+  });
+  it('should throw when lower is out of range', function () {
+    assert.throws(
+      () => sharp().normalise({ lower: -10 }),
+      /Expected number between 0 and 99 for lower but received -10 of type number/
+    );
+  });
+  it('should throw when upper is out of range', function () {
+    assert.throws(
+      () => sharp().normalise({ upper: 110 }),
+      /Expected number between 1 and 100 for upper but received 110 of type number/
+    );
+  });
+  it('should throw when lower is not a number', function () {
+    assert.throws(
+      () => sharp().normalise({ lower: 'fail' }),
+      /Expected number between 0 and 99 for lower but received fail of type string/
+    );
+  });
+  it('should throw when upper is not a number', function () {
+    assert.throws(
+      () => sharp().normalise({ upper: 'fail' }),
+      /Expected number between 1 and 100 for upper but received fail of type string/
+    );
+  });
+  it('should throw when the lower and upper are equal', function () {
+    assert.throws(
+      () => sharp().normalise({ lower: 2, upper: 2 }),
+      /Expected lower to be less than upper for range but received 2 >= 2/
+    );
+  });
+  it('should throw when the lower is greater than upper', function () {
+    assert.throws(
+      () => sharp().normalise({ lower: 3, upper: 2 }),
+      /Expected lower to be less than upper for range but received 3 >= 2/
+    );
+  });
 });