Optimizer: Always replace images to ensure baseline JPEG encoding

Author: bigbag

README.md

@@ -31,7 +31,7 @@ A tool for converting EPUB files to XTC/XTCH format and optimizing EPUBs for e-i
   - Resize images to configurable max width/height
   - Flatten alpha transparency to white background
   - Skip tiny decorative images (<20px)
-  - Only replace images when processed version is smaller
+  - Re-encode images to baseline JPEG (required by e-paper devices)
 - Remove unsupported image formats (SVG, WebP, TIFF)
 - Inject e-paper optimized CSS
 - Batch processing with ZIP export

cli/optimizer.js

@@ -283,7 +283,7 @@ async function optimizeEpub(inputPath, outputPath, options) {
         if (options.processImages && /\.(jpg|jpeg|png|bmp)$/i.test(filePath)) {
             const imgData = await zipFile.async('nodebuffer');
             const processed = await processImage(imgData, options.maxImageWidth, options.grayscale);
-            if (processed && processed.length < imgData.length) {
+            if (processed) {
                 // Output is always JPEG — rename non-JPEG files to avoid content-type mismatch
                 if (/\.(png|bmp)$/i.test(filePath)) {
                     const jpegPath = filePath.replace(/\.[^.]+$/, '.jpg');
@@ -292,6 +292,8 @@ async function optimizeEpub(inputPath, outputPath, options) {
                     imageRenames[filePath] = jpegPath;
                     ops.push({ type: 'convertImage', file: filePath, to: jpegPath });
                 } else {
+                    // Always replace JPEGs — device requires baseline encoding
+                    // (progressive and arithmetic JPEGs are re-encoded to baseline by Sharp)
                     epubZip.file(filePath, processed);
                     ops.push({ type: 'processImage', file: filePath });
                 }

web/app.js

@@ -1814,7 +1814,7 @@ async function optimizeEpub(file) {
         if (settings.processImages && /\.(jpg|jpeg|png|bmp|gif)$/i.test(path)) {
             var imgData = await zipFile.async('arraybuffer');
             var processedImg = await processImage(imgData, settings.maxWidth, settings.grayscale);
-            if (processedImg && processedImg.byteLength < imgData.byteLength) {
+            if (processedImg) {
                 epubZip.file(path, processedImg);
             }
         }