WIP to allow setting a background color

lib/postprocessing/image.js

@@ -91,7 +91,8 @@ const EXTRA_INSTRUCTIONS = new Set([
     "interlace",
     "dpi",
     "convertToDpi",
-    "watermark"
+    "watermark",
+    "pdfbgcolor"
 ]);
 
 const SRGB_COLOR_PROFILE_FILE = process.env.SRGB_COLOR_PROFILE_FILE;
@@ -191,7 +192,6 @@ function isTargetFormat(metadata, instructions) {
     if (format) {
         return metadata.FileType === format;
     }
-
     return false;
 }
 
@@ -473,7 +473,7 @@ async function applyOperations(img, intermediateRendition, rendition, directorie
         img = convertSvg(img, instructions);
     } else {
         // raster
-        img = handleTransparency(img, instructions.fmt);
+        img = handleTransparency(img, instructions);
     }
 
     // handle exif orientation
@@ -623,12 +623,10 @@ async function write(img, outfile) {
  * @param {Object} directories working directories of the current activation
  */
 async function imagePostProcess(intermediateRendition, rendition, directories) {
-
     const img = await read(intermediateRendition.path);
     img.setFormat(rendition.instructions.fmt);
 
     await applyOperations(img, intermediateRendition, rendition, directories);
-
     await applyOutputProperties(img, rendition.instructions);
 
     await write(img, rendition.path);
@@ -639,23 +637,29 @@ function convertSvg(img, instructions) {
     // Only using width because ImageMagick will use the smallest value whether it be width or height
     const width = instructions.width || SVG_DEFAULT_WIDTH;
 
-    img = handleTransparency(img, instructions.fmt);
+    img = handleTransparency(img, instructions);
 
     // some svgs have no size (only percentage width/height), so we scale them to our target size
     img.in("-size", `${width}`); // 2020-11-10 img.rawSize() will not be applied at the correct time and the SVG will be upscaled resulting in a fuzzy final rendition
     return img;
 }
 
-// gm("img.png").set(attribute, value)
-function handleTransparency(img, fmt) {
-    if (FORMAT_SUPPORTS_TRANSPARENCY[fmt]) {
+function handleTransparency(img, instructions) {
+  if(instructions.pdfbgcolor) {
+    // replacing transparency with a color defined in instructions
+    // (disregard if the format supports keeping transparency or not)
+    img.background(instructions.pdfbgcolor);
+    img.flatten();
+  } else {
+    if (FORMAT_SUPPORTS_TRANSPARENCY[instructions.fmt]) {
         img.background(DEFAULT_TRANSPARENCCY_BACKGROUND); // Keep transparency
     } else {
-        img.background(DEFAULT_BACKGROUND_COLOR); // Change tranparency background to default background color 
+        img.background(DEFAULT_BACKGROUND_COLOR); // Change tranparency background to default background color
         img.flatten();  // forces the image on its background to "commit" the background
     }
 
     return img;
+  }
 }
 
 module.exports = {