fix: handle interlaced PNG with indexed transparency

CHANGELOG.md

@@ -5,6 +5,7 @@
 - Fix garbled text copying in Chrome/Edge for PDFs with >256 unique characters (#1659)
 - Fix Link accessibility issues
 - Fix Table Accessibility Issue: Operator CS/cs not allowed in this current state
+- Fix Interlaced PNG with indexed transparency rendered incorrectly
 - Preserve existing PageMode instead of overwriting when adding outlines
 
 ### [v0.17.2] - 2025-08-30

lib/image/png.js

@@ -150,6 +150,7 @@ class PNGImage {
 
   loadIndexedAlphaChannel() {
     const transparency = this.image.transparency.indexed;
+    const isInterlaced = this.image.interlaceMethod === 1;
     return this.image.decodePixels((pixels) => {
       const alphaChannel = Buffer.alloc(this.width * this.height);
 
@@ -158,6 +159,11 @@ class PNGImage {
         alphaChannel[i++] = transparency[pixels[j]];
       }
 
+      // For interlaced images, re-encode the decoded pixel data
+      if (isInterlaced) {
+        this.imgData = zlib.deflateSync(Buffer.from(pixels));
+      }
+
       this.alphaChannel = zlib.deflateSync(alphaChannel);
       return this.finalize();
     });

tests/visual/interlaced-png.spec.js

@@ -0,0 +1,76 @@
+import { runDocTest } from './helpers';
+
+describe('interlaced PNG (Adam7)', function () {
+  test('interlaced grayscale renders correctly', function () {
+    return runDocTest(function (doc) {
+      doc.font('tests/fonts/Roboto-Regular.ttf');
+      doc.fontSize(12);
+
+      doc.text('Interlaced Grayscale PNG (Adam7)', 50, 30);
+      doc.image('tests/images/interlaced-grayscale-8bit.png', 50, 50, {
+        width: 100,
+      });
+    });
+  });
+
+  test('interlaced RGB renders correctly', function () {
+    return runDocTest(function (doc) {
+      doc.font('tests/fonts/Roboto-Regular.ttf');
+      doc.fontSize(12);
+
+      doc.text('Interlaced RGB PNG (Adam7)', 50, 30);
+      doc.image('tests/images/interlaced-rgb-8bit.png', 50, 50, {
+        width: 100,
+      });
+    });
+  });
+
+  test('interlaced RGB 16bit renders correctly', function () {
+    return runDocTest(function (doc) {
+      doc.font('tests/fonts/Roboto-Regular.ttf');
+      doc.fontSize(12);
+
+      doc.text('Interlaced RGB 16-bit PNG (Adam7)', 50, 30);
+      doc.image('tests/images/interlaced-rgb-16bit.png', 50, 50, {
+        width: 100,
+      });
+    });
+  });
+
+  test('interlaced palette renders correctly', function () {
+    return runDocTest(function (doc) {
+      doc.font('tests/fonts/Roboto-Regular.ttf');
+      doc.fontSize(12);
+
+      doc.text('Interlaced Palette PNG (Adam7)', 50, 30);
+      doc.image('tests/images/interlaced-pallete-8bit.png', 50, 50, {
+        width: 100,
+      });
+    });
+  });
+
+  test('interlaced RGBA renders correctly', function () {
+    return runDocTest(function (doc) {
+      doc.font('tests/fonts/Roboto-Regular.ttf');
+      doc.fontSize(12);
+
+      doc.text('Interlaced RGBA PNG (Adam7)', 50, 30);
+      doc.image('tests/images/interlaced-rgb-alpha-8bit.png', 50, 50, {
+        width: 100,
+      });
+    });
+  });
+
+  // https://github.com/foliojs/pdfkit/issues/414
+  test('issue #414 - interlaced palette PNG renders correctly', function () {
+    return runDocTest(function (doc) {
+      doc.font('tests/fonts/Roboto-Regular.ttf');
+      doc.fontSize(12);
+
+      doc.text('Issue #414: Interlaced Palette PNG', 50, 30);
+      doc.image('tests/images/issue-414-interlaced.png', 50, 50, {
+        width: 300,
+      });
+    });
+  });
+});