Add removeAlpha op, removes alpha channel if any #1248

src/operations.cc

@@ -28,6 +28,16 @@ using vips::VError;
 
 namespace sharp {
 
+  /*
+    Removes alpha channel, if any.
+  */
+  VImage RemoveAlpha(VImage image) {
+    if (HasAlpha(image)) {
+      image = image.extract_band(0, VImage::option()->set("n", image.bands() - 1));
+    }
+    return image;
+  }
+
   /*
     Composite overlayImage over image at given position
     Assumes alpha channels are already premultiplied and will be unpremultiplied after
@@ -223,10 +233,8 @@ namespace sharp {
   VImage Gamma(VImage image, double const exponent) {
     if (HasAlpha(image)) {
       // Separate alpha channel
-      VImage imageWithoutAlpha = image.extract_band(0,
-        VImage::option()->set("n", image.bands() - 1));
       VImage alpha = image[image.bands() - 1];
-      return imageWithoutAlpha.gamma(VImage::option()->set("exponent", exponent)).bandjoin(alpha);
+      return RemoveAlpha(image).gamma(VImage::option()->set("exponent", exponent)).bandjoin(alpha);
     } else {
       return image.gamma(VImage::option()->set("exponent", exponent));
     }
@@ -374,10 +382,8 @@ namespace sharp {
   VImage Linear(VImage image, double const a, double const b) {
     if (HasAlpha(image)) {
       // Separate alpha channel
-      VImage imageWithoutAlpha = image.extract_band(0,
-        VImage::option()->set("n", image.bands() - 1));
       VImage alpha = image[image.bands() - 1];
-      return imageWithoutAlpha.linear(a, b).bandjoin(alpha);
+      return RemoveAlpha(image).linear(a, b).bandjoin(alpha);
     } else {
       return image.linear(a, b);
     }

src/operations.h

@@ -25,6 +25,11 @@ using vips::VImage;
 
 namespace sharp {
 
+  /*
+    Removes alpha channel, if any.
+  */
+  VImage RemoveAlpha(VImage image);
+
   /*
     Alpha composite src over dst with given gravity.
     Assumes alpha channels are already premultiplied and will be unpremultiplied after.

src/pipeline.cc

@@ -698,6 +698,12 @@ class PipelineWorker : public Nan::AsyncWorker {
           .extract_band(baton->extractChannel)
           .copy(VImage::option()->set("interpretation", VIPS_INTERPRETATION_B_W));
       }
+
+      // Remove alpha channel, if any
+      if (baton->removeAlpha) {
+        image = sharp::RemoveAlpha(image);
+      }
+
       // Convert image to sRGB, if not already
       if (sharp::Is16Bit(image.interpretation())) {
         image = image.cast(VIPS_FORMAT_USHORT);
@@ -1235,6 +1241,7 @@ NAN_METHOD(pipeline) {
   baton->extendLeft = AttrTo<int32_t>(options, "extendLeft");
   baton->extendRight = AttrTo<int32_t>(options, "extendRight");
   baton->extractChannel = AttrTo<int32_t>(options, "extractChannel");
+  baton->removeAlpha = AttrTo<bool>(options, "removeAlpha");
   if (HasAttr(options, "boolean")) {
     baton->boolean = CreateInputDescriptor(AttrAs<v8::Object>(options, "boolean"), buffersToPersist);
     baton->booleanOp = sharp::GetBooleanOperation(AttrAsStr(options, "booleanOp"));

src/pipeline.h

@@ -131,6 +131,7 @@ struct PipelineBaton {
   VipsOperationBoolean booleanOp;
   VipsOperationBoolean bandBoolOp;
   int extractChannel;
+  bool removeAlpha;
   VipsInterpretation colourspace;
   int tileSize;
   int tileOverlap;
@@ -213,6 +214,7 @@ struct PipelineBaton {
     booleanOp(VIPS_OPERATION_BOOLEAN_LAST),
     bandBoolOp(VIPS_OPERATION_BOOLEAN_LAST),
     extractChannel(-1),
+    removeAlpha(false),
     colourspace(VIPS_INTERPRETATION_LAST),
     tileSize(256),
     tileOverlap(0),