Repository: lovell/sharp
Pull request #4207 (2024-09-03 20:11:29)

Add PDF background color option
Fixes https://github.com/lovell/sharp/issues/3321.

I followed existing code for `options.subifd` and `options.create.background` to pass a [`background` option to vips](https://www.libvips.org/API/current/VipsForeignSave.html#vips-pdfload) for rendering PDFs. I _haven't tested that this works_ with a vips build containing PDF support. Instead of using `sharp`'s global vips support I override the contents of the `@img/sharp-libvips-*` packages with my own custom builds derived from https://github.com/lovell/sharp-libvips which makes testing custom sharp C code a little more difficult.

If you’re not sure this is the right way to pass the `background` option to `vips_pdfload()` ([source](https://www.libvips.org/API/current/VipsForeignSave.html#vips-pdfload)) I can try to jump through some hoops to see if this change works in my local setup.


Patch:
diff --git a/docs/api-constructor.md b/docs/api-constructor.md
index 22bab9f1..2d31c86b 100644
--- a/docs/api-constructor.md
+++ b/docs/api-constructor.md
@@ -40,6 +40,7 @@ where the overall height is the `pageHeight` multiplied by the number of `pages`
 | [options.page] | <code>number</code> | <code>0</code> | Page number to start extracting from for multi-page input (GIF, WebP, TIFF), zero based. |
 | [options.subifd] | <code>number</code> | <code>-1</code> | subIFD (Sub Image File Directory) to extract for OME-TIFF, defaults to main image. |
 | [options.level] | <code>number</code> | <code>0</code> | level to extract from a multi-level input (OpenSlide), zero based. |
+| [options.pdfBackground] | <code>string</code> \| <code>Object</code> |  | Background color to use when PDF is partially transparent. Parsed by the [color](https://www.npmjs.org/package/color) module to extract values for red, green, blue and alpha. Requires the use of a globally-installed libvips compiled with support for PDFium, poppler-glib, ImageMagick, or GraphicsMagick. |
 | [options.animated] | <code>boolean</code> | <code>false</code> | Set to `true` to read all frames/pages of an animated image (GIF, WebP, TIFF), equivalent of setting `pages` to `-1`. |
 | [options.raw] | <code>Object</code> |  | describes raw pixel input image data. See `raw()` for pixel ordering. |
 | [options.raw.width] | <code>number</code> |  | integral number of pixels wide. |
diff --git a/docs/search-index.json b/docs/search-index.json
index 634d7cc9..5d9d720a 100644
--- a/docs/search-index.json
+++ b/docs/search-index.json
@@ -1,1 +1,1 @@
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\ No newline at end of file
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This operation will always occur after resizing and extraction, if a","k":"extend pad extrude edges background colour pixels derived operation resizing extraction","l":"/api-resize#extend"},{"t":"extract","d":"Extract/crop a region of the image.","k":"extract crop region left top width height","l":"/api-resize#extract"},{"t":"trim","d":"Trim pixels from all edges that contain values similar to the given background colour, which defaults to that of the top-left pixel.","k":"trim pixels edges contain similar background colour defaults top left pixel threshold line art","l":"/api-resize#trim"},{"t":"composite","d":"Composite images over the processed resized, extracted etc. image.","k":"composite images processed resized extracted","l":"/api-composite#composite"},{"t":"rotate","d":"Rotate the output image by either an explicit angle or auto-orient based on the EXIF Orientation tag.","k":"rotate output explicit angle auto orient exif orientation tag background","l":"/api-operation#rotate"},{"t":"flip","d":"Mirror the image vertically up-down about the x-axis. This always occurs before rotation, if any.","k":"flip mirror vertically down axis rotation","l":"/api-operation#flip"},{"t":"flop","d":"Mirror the image horizontally left-right about the y-axis. This always occurs before rotation, if any.","k":"flop mirror horizontally left right axis rotation","l":"/api-operation#flop"},{"t":"affine","d":"Perform an affine transform on an image. This operation will always occur after resizing, extraction and rotation, if any.","k":"affine transform operation resizing extraction rotation background idx idy odx ody interpolator","l":"/api-operation#affine"},{"t":"sharpen","d":"Sharpen the image.","k":"sharpen sigma","l":"/api-operation#sharpen"},{"t":"median","d":"Apply median filter. When used without parameters the default window is 3x3.","k":"median apply filter parameters window","l":"/api-operation#median"},{"t":"blur","d":"Blur the image.","k":"blur sigma precision min amplitude","l":"/api-operation#blur"},{"t":"flatten","d":"Merge alpha transparency channel, if any, with a background, then remove the alpha channel.","k":"flatten merge alpha transparency channel background remove","l":"/api-operation#flatten"},{"t":"unflatten","d":"Ensure the image has an alpha channel with all white pixel values made fully transparent.","k":"unflatten alpha channel white pixel made fully transparent","l":"/api-operation#unflatten"},{"t":"gamma","d":"Apply a gamma correction by reducing the encoding darken pre-resize at a factor of 1/gamma then increasing the encoding brighten post-resize at a factor of gamma. This can improve the perceived brigh","k":"gamma apply correction reducing encoding darken resize factor increasing brighten post improve perceived brigh alpha","l":"/api-operation#gamma"},{"t":"normalise","d":"Enhance output image contrast by stretching its luminance to cover a full dynamic range.","k":"normalise enhance output contrast stretching luminance cover full dynamic range lower upper","l":"/api-operation#normalise"},{"t":"normalize","d":"Alternative spelling of normalise.","k":"normalize normalise lower upper","l":"/api-operation#normalize"},{"t":"clahe","d":"Perform contrast limiting adaptive histogram equalization CLAHE.","k":"clahe contrast limiting adaptive histogram equalization width height max slope","l":"/api-operation#clahe"},{"t":"convolve","d":"Convolve the image with the specified kernel.","k":"convolve kernel","l":"/api-operation#convolve"},{"t":"threshold","d":"Any pixel value greater than or equal to the threshold value will be set to 255, otherwise it will be set to 0.","k":"threshold pixel greater equal otherwise greyscale grayscale raw","l":"/api-operation#threshold"},{"t":"recomb","d":"Recombine the image with the specified matrix.","k":"recomb recombine matrix","l":"/api-operation#recomb"},{"t":"modulate","d":"Transforms the image using brightness, saturation, hue rotation, and lightness. Brightness and lightness both operate on luminance, with the difference being that brightness is multiplicative whereas","k":"modulate transforms brightness saturation hue rotation lightness operate luminance difference being multiplicative whereas","l":"/api-operation#modulate"},{"t":"removeAlpha","d":"Remove alpha channel, if any. This is a no-op if the image does not have an alpha channel.","k":"removealpha remove alpha channel","l":"/api-channel#removealpha"},{"t":"ensureAlpha","d":"Ensure the output image has an alpha transparency channel. If missing, the added alpha channel will have the specified transparency level, defaulting to fully-opaque 1. This is a no-op if the image a","k":"ensurealpha output alpha transparency channel missing added level defaulting fully opaque","l":"/api-channel#ensurealpha"},{"t":"extractChannel","d":"Extract a single channel from a multi-channel image.","k":"extractchannel extract single channel multi","l":"/api-channel#extractchannel"},{"t":"joinChannel","d":"Join one or more channels to the image. The meaning of the added channels depends on the output colourspace, set with toColourspace. By default the output image will be web-friendly sRGB, with additi","k":"joinchannel join channels added depends output colourspace tocolourspace web friendly srgb additi","l":"/api-channel#joinchannel"},{"t":"tint","d":"Tint the image using the provided colour. An alpha channel may be present and will be unchanged by the operation.","k":"tint colour alpha channel present unchanged operation","l":"/api-colour#tint"},{"t":"greyscale","d":"Convert to 8-bit greyscale 256 shades of grey. This is a linear operation. If the input image is in a non-linear colour space such as sRGB, use gamma with greyscale for the best results. By default t","k":"greyscale convert bit shades grey linear operation input colour space srgb gamma results","l":"/api-colour#greyscale"},{"t":"grayscale","d":"Alternative spelling of greyscale.","k":"grayscale greyscale","l":"/api-colour#grayscale"},{"t":"pipelineColorspace","d":"Alternative spelling of pipelineColourspace.","k":"","l":"/api-colour#pipelinecolorspace"},{"t":"versions","d":"An Object containing the version numbers of sharp, libvips and when using prebuilt binaries its dependencies.","k":"versions object version numbers libvips prebuilt binaries dependencies","l":"/api-utility#versions"},{"t":"interpolators","d":"An Object containing the available interpolators and their proper values","k":"interpolators object","l":"/api-utility#interpolators"},{"t":"queue","d":"An EventEmitter that emits a change event when a task is either - queued, waiting for _libuv_ to provide a worker thread - complete","k":"queue eventemitter emits change event queued waiting libuv worker thread complete","l":"/api-utility#queue"},{"t":"cache","d":"Gets or, when options are provided, sets the limits of _libvips_ operation cache. Existing entries in the cache will be trimmed after any change in limits. This method always returns cache statistics","k":"cache limits libvips operation existing entries trimmed change method returns statistics memory files items","l":"/api-utility#cache"},{"t":"concurrency","d":"Gets or, when a concurrency is provided, sets the maximum number of threads _libvips_ should use to process _each image_. These are from a thread pool managed by glib, which helps avoid the overhead","k":"concurrency maximum number threads libvips process thread pool managed glib avoid overhead","l":"/api-utility#concurrency"},{"t":"counters","d":"Provides access to internal task counters. - queue is the number of tasks this module has queued waiting for _libuv_ to provide a worker thread from its pool. - process is the number of resize tasks","k":"counters provides access internal queue number tasks module queued waiting libuv worker thread pool process resize","l":"/api-utility#counters"},{"t":"simd","d":"Get and set use of SIMD vector unit instructions. Requires libvips to have been compiled with highway support.","k":"simd vector unit instructions libvips compiled highway","l":"/api-utility#simd"},{"t":"block","d":"Block libvips operations at runtime.","k":"block libvips operations runtime operation","l":"/api-utility#block"},{"t":"unblock","d":"Unblock libvips operations at runtime.","k":"unblock libvips operations runtime operation","l":"/api-utility#unblock"}]
\ No newline at end of file
diff --git a/lib/constructor.js b/lib/constructor.js
index 41f78020..3150d1ef 100644
--- a/lib/constructor.js
+++ b/lib/constructor.js
@@ -139,6 +139,7 @@ const debuglog = util.debuglog('sharp');
  * @param {number} [options.page=0] - Page number to start extracting from for multi-page input (GIF, WebP, TIFF), zero based.
  * @param {number} [options.subifd=-1] - subIFD (Sub Image File Directory) to extract for OME-TIFF, defaults to main image.
  * @param {number} [options.level=0] - level to extract from a multi-level input (OpenSlide), zero based.
+ * @param {string|Object} [options.pdfBackground] - Background color to use when PDF is partially transparent. Parsed by the [color](https://www.npmjs.org/package/color) module to extract values for red, green, blue and alpha. Requires the use of a globally-installed libvips compiled with support for PDFium, poppler-glib, ImageMagick, or GraphicsMagick.
  * @param {boolean} [options.animated=false] - Set to `true` to read all frames/pages of an animated image (GIF, WebP, TIFF), equivalent of setting `pages` to `-1`.
  * @param {Object} [options.raw] - describes raw pixel input image data. See `raw()` for pixel ordering.
  * @param {number} [options.raw.width] - integral number of pixels wide.
@@ -348,6 +349,7 @@ const Sharp = function (input, options) {
     timeoutSeconds: 0,
     linearA: [],
     linearB: [],
+    pdfBackground: [255, 255, 255, 255],
     // Function to notify of libvips warnings
     debuglog: warning => {
       this.emit('warning', warning);
diff --git a/lib/index.d.ts b/lib/index.d.ts
index 7fba55f7..7411bc23 100644
--- a/lib/index.d.ts
+++ b/lib/index.d.ts
@@ -935,6 +935,8 @@ declare namespace sharp {
         subifd?: number | undefined;
         /** Level to extract from a multi-level input (OpenSlide), zero based. (optional, default 0) */
         level?: number | undefined;
+        /** Background color to use when PDF is partially transparent. Requires the use of a globally-installed libvips compiled with support for PDFium, poppler-glib, ImageMagick, or GraphicsMagick. */
+        pdfBackground?: Color | undefined;
         /** Set to `true` to read all frames/pages of an animated image (equivalent of setting `pages` to `-1`). (optional, default false) */
         animated?: boolean | undefined;
         /** Describes raw pixel input image data. See raw() for pixel ordering. */
diff --git a/lib/input.js b/lib/input.js
index 93d4e741..9e06fafe 100644
--- a/lib/input.js
+++ b/lib/input.js
@@ -24,8 +24,8 @@ const align = {
  * @private
  */
 function _inputOptionsFromObject (obj) {
-  const { raw, density, limitInputPixels, ignoreIcc, unlimited, sequentialRead, failOn, failOnError, animated, page, pages, subifd } = obj;
-  return [raw, density, limitInputPixels, ignoreIcc, unlimited, sequentialRead, failOn, failOnError, animated, page, pages, subifd].some(is.defined)
+  const { raw, density, limitInputPixels, ignoreIcc, unlimited, sequentialRead, failOn, failOnError, animated, page, pages, subifd, pdfBackground } = obj;
+  return [raw, density, limitInputPixels, ignoreIcc, unlimited, sequentialRead, failOn, failOnError, animated, page, pages, subifd, pdfBackground].some(is.defined)
     ? { raw, density, limitInputPixels, ignoreIcc, unlimited, sequentialRead, failOn, failOnError, animated, page, pages, subifd }
     : undefined;
 }
@@ -222,6 +222,10 @@ function _createInputDescriptor (input, inputOptions, containerOptions) {
         throw is.invalidParameterError('subifd', 'integer between -1 and 100000', inputOptions.subifd);
       }
     }
+    // PDF background color
+    if (is.defined(inputOptions.pdfBackground)) {
+      this._setBackgroundColourOption('pdfBackground', inputOptions.pdfBackground);
+    }
     // Create new image
     if (is.defined(inputOptions.create)) {
       if (
diff --git a/src/common.cc b/src/common.cc
index 00aa8069..1d6a8f63 100644
--- a/src/common.cc
+++ b/src/common.cc
@@ -109,6 +109,10 @@ namespace sharp {
     if (HasAttr(input, "subifd")) {
       descriptor->subifd = AttrAsInt32(input, "subifd");
     }
+    // // PDF background color
+    if (HasAttr(input, "pdfBackground")) {
+      descriptor->pdfBackground = AttrAsVectorOfDouble(input, "pdfBackground");
+    }
     // Create new image
     if (HasAttr(input, "createChannels")) {
       descriptor->createChannels = AttrAsUint32(input, "createChannels");
@@ -402,6 +406,9 @@ namespace sharp {
             if (imageType == ImageType::TIFF) {
               option->set("subifd", descriptor->subifd);
             }
+            if (imageType == ImageType::PDF) {
+              option->set("background", descriptor->pdfBackground);
+            }
             image = VImage::new_from_buffer(descriptor->buffer, descriptor->bufferLength, nullptr, option);
             if (imageType == ImageType::SVG || imageType == ImageType::PDF || imageType == ImageType::MAGICK) {
               image = SetDensity(image, descriptor->density);
@@ -506,6 +513,9 @@ namespace sharp {
             if (imageType == ImageType::TIFF) {
               option->set("subifd", descriptor->subifd);
             }
+            if (imageType == ImageType::PDF) {
+              option->set("background", descriptor->pdfBackground);
+            }
             image = VImage::new_from_file(descriptor->file.data(), option);
             if (imageType == ImageType::SVG || imageType == ImageType::PDF || imageType == ImageType::MAGICK) {
               image = SetDensity(image, descriptor->density);
diff --git a/src/common.h b/src/common.h
index 225f6129..499f03a2 100644
--- a/src/common.h
+++ b/src/common.h
@@ -74,6 +74,7 @@ namespace sharp {
     int textSpacing;
     VipsTextWrap textWrap;
     int textAutofitDpi;
+    std::vector<double> pdfBackground;
 
     InputDescriptor():
       buffer(nullptr),
@@ -108,7 +109,8 @@ namespace sharp {
       textRgba(false),
       textSpacing(0),
       textWrap(VIPS_TEXT_WRAP_WORD),
-      textAutofitDpi(0) {}
+      textAutofitDpi(0),
+      pdfBackground{ 255.0, 255.0, 255.0, 255.0 } {}
   };
 
   // Convenience methods to access the attributes of a Napi::Object


Test patch:
diff --git a/test/unit/io.js b/test/unit/io.js
index bdb4c9ce..98b96a57 100644
--- a/test/unit/io.js
+++ b/test/unit/io.js
@@ -893,6 +893,27 @@ describe('Input/output', function () {
         sharp({ subifd: 1.2 });
       }, /Expected integer between -1 and 100000 for subifd but received 1.2 of type number/);
     });
+    it('Valid pdfBackground property (string)', function () {
+      sharp({ pdfBackground: '#00ff00' });
+    });
+    it('Valid pdfBackground property (object)', function () {
+      sharp({ pdfBackground: { r: 0, g: 255, b: 0 } });
+    });
+    it('Invalid pdfBackground property (string) throws', function () {
+      assert.throws(function () {
+        sharp({ pdfBackground: '00ff00' });
+      }, /Unable to parse color from string/);
+    });
+    it('Invalid pdfBackground property (number) throws', function () {
+      assert.throws(function () {
+        sharp({ pdfBackground: 255 });
+      }, /Expected object or string for background/);
+    });
+    it('Invalid pdfBackground property (object)', function () {
+      assert.throws(function () {
+        sharp({ pdfBackground: { red: 0, green: 255, blue: 0 } });
+      }, /Unable to parse color from object/);
+    });
   });
 
   it('Fails when writing to missing directory', async () => {