Add option to save PNG without transparency

app.js

@@ -97,8 +97,11 @@ conversionRouter.post('/convert', async (req, res) => {
 
     // Convert to PNG
     } else if (fileFormat === 'png') {
-      await sharp(inputSvgFileName, { density: 96 })
+      let s = sharp(inputSvgFileName, { density: 96 });
-        .toFile(outputFileName); // Sharp's PNG type is implicitly determined via the output file extension
+      if (req.body.transparentBackground === 'false') {
+        s = s.flatten({ background: { r: 255, g: 255, b: 255 } });
+      }
+      await s.toFile(outputFileName); // Sharp's PNG type is implicitly determined via the output file extension
 
     // Convert to JPG
     } else {

static/index.html

@@ -68,6 +68,14 @@
                                 </label>
                             </div>
                         </div>
+                        <div class="form-group">
+                            <div class="form-check">
+                                <input class="form-check-input" type="checkbox" id="transparentBackgroundCheckbox" checked>
+                                <label class="form-check-label" for="transparentBackgroundCheckbox">
+                                  Transparent background (for PNG)
+                                </label>
+                            </div>
+                        </div>
                         <button class="btn btn-primary" type="button" id="convertButton">
                             <span class="spinner-grow spinner-grow-sm d-none" role="status" aria-hidden="true" id="convertSpinner"></span>
                             <span id="convertButtonText">Convert</span>

static/latex2image-client.js

@@ -57,7 +57,8 @@ $(document).ready(function() {
       data: {
         latexInput: latexInput,
         outputFormat: $('#outputFormatSelect').val(),
-        outputScale: $('#outputScaleSelect').val()
+        outputScale: $('#outputScaleSelect').val(),
+        transparentBackground: $('#transparentBackgroundCheckbox').prop('checked'),
       },
       success: function(data) {
         $('#convertButton').prop('disabled', false);