Switch from custom trim op to vips_find_trim #914

docs/changelog.md

@@ -19,6 +19,9 @@ Requires libvips v8.7.0.
     Per-operation `background` options added to `resize`, `extend` and `flatten` operations.
   [#1392](https://github.com/lovell/sharp/issues/1392)
 
+* Switch from custom trim operation to `vips_find_trim`.
+  [#914](https://github.com/lovell/sharp/issues/914)
+
 * Drop Node 4 support.
   [#1212](https://github.com/lovell/sharp/issues/1212)
 

lib/constructor.js

@@ -134,7 +134,7 @@ const Sharp = function (input, options) {
     sharpenJagged: 2,
     threshold: 0,
     thresholdGrayscale: true,
-    trimTolerance: 0,
+    trimThreshold: 0,
     gamma: 0,
     greyscale: false,
     normalise: 0,

lib/resize.js

@@ -359,18 +359,18 @@ function extract (options) {
 }
 
 /**
- * Trim "boring" pixels from all edges that contain values within a percentage similarity of the top-left pixel.
- * @param {Number} [tolerance=10] value between 1 and 99 representing the percentage similarity.
+ * Trim "boring" pixels from all edges that contain values similar to the top-left pixel.
+ * @param {Number} [threshold=10] the allowed difference from the top-left pixel, a number greater than zero.
  * @returns {Sharp}
  * @throws {Error} Invalid parameters
  */
-function trim (tolerance) {
-  if (!is.defined(tolerance)) {
-    this.options.trimTolerance = 10;
-  } else if (is.integer(tolerance) && is.inRange(tolerance, 1, 99)) {
-    this.options.trimTolerance = tolerance;
+function trim (threshold) {
+  if (!is.defined(threshold)) {
+    this.options.trimThreshold = 10;
+  } else if (is.number(threshold) && threshold > 0) {
+    this.options.trimThreshold = threshold;
   } else {
-    throw new Error('Invalid trim tolerance (1 to 99) ' + tolerance);
+    throw is.invalidParameterError('threshold', 'number greater than zero', threshold);
   }
   return this;
 }

src/operations.cc

@@ -324,55 +324,21 @@ namespace sharp {
     return image.boolean(imageR, boolean);
   }
 
-  VImage Trim(VImage image, int const tolerance) {
-    using sharp::MaximumImageAlpha;
-    // An equivalent of ImageMagick's -trim in C++ ... automatically remove
-    // "boring" image edges.
-
-    // We use .project to sum the rows and columns of a 0/255 mask image, the first
-    // non-zero row or column is the object edge. We make the mask image with an
-    // amount-different-from-background image plus a threshold.
-
-    // find the value of the pixel at (0, 0) ... we will search for all pixels
-    // significantly different from this
-    std::vector<double> background = image(0, 0);
-
-    double const max = MaximumImageAlpha(image.interpretation());
-
-    // we need to smooth the image, subtract the background from every pixel, take
-    // the absolute value of the difference, then threshold
-    VImage mask = (image.median(3) - background).abs() > (max * tolerance / 100);
-
-    // sum mask rows and columns, then search for the first non-zero sum in each
-    // direction
-    VImage rows;
-    VImage columns = mask.project(&rows);
-
-    VImage profileLeftV;
-    VImage profileLeftH = columns.profile(&profileLeftV);
-
-    VImage profileRightV;
-    VImage profileRightH = columns.fliphor().profile(&profileRightV);
-
-    VImage profileTopV;
-    VImage profileTopH = rows.profile(&profileTopV);
-
-    VImage profileBottomV;
-    VImage profileBottomH = rows.flipver().profile(&profileBottomV);
-
-    int left = static_cast<int>(floor(profileLeftV.min()));
-    int right = columns.width() - static_cast<int>(floor(profileRightV.min()));
-    int top = static_cast<int>(floor(profileTopH.min()));
-    int bottom = rows.height() - static_cast<int>(floor(profileBottomH.min()));
-
-    int width = right - left;
-    int height = bottom - top;
-
-    if (width <= 0 || height <= 0) {
+  /*
+    Trim an image
+  */
+  VImage Trim(VImage image, int const threshold) {
+    // Top-left pixel provides the background colour
+    VImage background = image.extract_area(0, 0, 1, 1);
+    if (HasAlpha(background)) {
+      background = background.flatten();
+    }
+    int top, width, height;
+    int const left = image.find_trim(&top, &width, &height,
+      VImage::option()->set("background", background(0, 0)));
+    if (width == 0 || height == 0) {
       throw VError("Unexpected error while trimming. Try to lower the tolerance");
     }
-
-    // and now crop the original image
     return image.extract_area(left, top, width, height);
   }
 

src/operations.h

@@ -100,7 +100,7 @@ namespace sharp {
   /*
     Trim an image
   */
-  VImage Trim(VImage image, int const tolerance);
+  VImage Trim(VImage image, int const threshold);
 
   /*
    * Linear adjustment (a * in + b)

src/pipeline.cc

@@ -100,8 +100,8 @@ class PipelineWorker : public Nan::AsyncWorker {
       }
 
       // Trim
-      if (baton->trimTolerance != 0) {
-        image = sharp::Trim(image, baton->trimTolerance);
+      if (baton->trimThreshold > 0.0) {
+        image = sharp::Trim(image, baton->trimThreshold);
       }
 
       // Pre extraction
@@ -233,7 +233,7 @@ class PipelineWorker : public Nan::AsyncWorker {
       if (
         xshrink == yshrink && xshrink >= 2 * shrink_on_load_factor &&
         (inputImageType == ImageType::JPEG || inputImageType == ImageType::WEBP) &&
-        baton->gamma == 0 && baton->topOffsetPre == -1 && baton->trimTolerance == 0
+        baton->gamma == 0 && baton->topOffsetPre == -1 && baton->trimThreshold == 0.0
       ) {
         if (xshrink >= 8 * shrink_on_load_factor) {
           xfactor = xfactor / 8;
@@ -1183,7 +1183,7 @@ NAN_METHOD(pipeline) {
   baton->sharpenJagged = AttrTo<double>(options, "sharpenJagged");
   baton->threshold = AttrTo<int32_t>(options, "threshold");
   baton->thresholdGrayscale = AttrTo<bool>(options, "thresholdGrayscale");
-  baton->trimTolerance = AttrTo<int32_t>(options, "trimTolerance");
+  baton->trimThreshold = AttrTo<double>(options, "trimThreshold");
   baton->gamma = AttrTo<double>(options, "gamma");
   baton->linearA = AttrTo<double>(options, "linearA");
   baton->linearB = AttrTo<double>(options, "linearB");
@@ -1293,7 +1293,7 @@ NAN_METHOD(pipeline) {
   }
   // Force random access for certain operations
   if (baton->accessMethod == VIPS_ACCESS_SEQUENTIAL && (
-    baton->trimTolerance != 0 || baton->normalise ||
+    baton->trimThreshold > 0.0 || baton->normalise ||
     baton->position == 16 || baton->position == 17)) {
     baton->accessMethod = VIPS_ACCESS_RANDOM;
   }

src/pipeline.h

@@ -81,7 +81,7 @@ struct PipelineBaton {
   double sharpenJagged;
   int threshold;
   bool thresholdGrayscale;
-  int trimTolerance;
+  double trimThreshold;
   double linearA;
   double linearB;
   double gamma;
@@ -176,7 +176,7 @@ struct PipelineBaton {
     sharpenJagged(2.0),
     threshold(0),
     thresholdGrayscale(true),
-    trimTolerance(0),
+    trimThreshold(0.0),
     linearA(1.0),
     linearB(0.0),
     gamma(0.0),

test/unit/trim.js

@@ -50,7 +50,7 @@ describe('Trim borders', function () {
   });
 
   describe('Invalid thresholds', function () {
-    [-1, 100, 'fail', {}].forEach(function (threshold) {
+    [-1, 'fail', {}].forEach(function (threshold) {
       it(JSON.stringify(threshold), function () {
         assert.throws(function () {
           sharp().trim(threshold);