diff --git a/elastic/templates/elastic/upload.html b/elastic/templates/elastic/upload.html
index 6cc1a75..e60eb28 100644
--- a/elastic/templates/elastic/upload.html
+++ b/elastic/templates/elastic/upload.html
@@ -139,6 +139,32 @@ const dropArea = document.getElementById('dropArea');
 
 let currentImageRel = '';
 
+async function convertToJpeg(file){
+  const url = URL.createObjectURL(file);
+  let img;
+  try{
+    const blob = await fetch(url).then(r=>r.blob());
+    img = await createImageBitmap(blob);
+  }catch(e){
+    img = await new Promise((resolve,reject)=>{const i=new Image();i.onload=()=>resolve(i);i.onerror=reject;i.src=url;});
+  }
+  URL.revokeObjectURL(url);
+  const maxDim = 2000;
+  const w = img.width;
+  const h = img.height;
+  const scale = Math.min(1, maxDim/Math.max(w,h));
+  const nw = Math.round(w*scale);
+  const nh = Math.round(h*scale);
+  const canvas = document.createElement('canvas');
+  canvas.width = nw;
+  canvas.height = nh;
+  const ctx = canvas.getContext('2d');
+  ctx.drawImage(img, 0, 0, nw, nh);
+  const blob = await new Promise(resolve=>canvas.toBlob(resolve,'image/jpeg',0.82));
+  const name = (file.name||'image').replace(/\.[^/.]+$/, '') + '.jpg';
+  return new File([blob], name, {type:'image/jpeg'});
+}
+
 // 拖拽上传功能
 ['dragenter', 'dragover', 'dragleave', 'drop'].forEach(eventName => {
   dropArea.addEventListener(eventName, preventDefaults, false);
@@ -289,8 +315,15 @@ uploadForm.addEventListener('submit', async (e) => {
     return;
   }
 
+  let jpegFile = file;
+  try {
+    jpegFile = await convertToJpeg(file);
+    preview.src = URL.createObjectURL(jpegFile);
+  } catch (_) {
+    jpegFile = file;
+  }
   const formData = new FormData();
-  formData.append('file', file);
+  formData.append('file', jpegFile);
 
   try {
     const resp = await fetch('/elastic/upload/', {
@@ -381,4 +414,4 @@ document.getElementById('logoutBtn').addEventListener('click', async () => {
 });
 </script>
 </body>
-</html>
\ No newline at end of file
+</html>