diff --git a/app/app.py b/app/app.py
index e2d8467..cb0401c 100644
--- a/app/app.py
+++ b/app/app.py
@@ -686,9 +686,11 @@ def check_resize():
     try:
         sizes = [int(s) for s in raw_sizes if int(s) in RESIZE_SIZES]
     except (ValueError, TypeError):
-        return jsonify({"conflicts": []})
+        sizes = []
 
     formats = [f for f in raw_formats if f in RESIZE_FORMATS]
+
+    src_ext = target.suffix.lstrip(".")
     stem    = re.sub(r"_\d+x\d+$", "", target.stem)
     parent  = target.parent
 
@@ -701,6 +703,19 @@ def check_resize():
         except (ValueError, TypeError):
             pass
 
+    # Pas de dimensions sélectionnées → conserver celles d'origine
+    if not all_dims:
+        try:
+            src = Image.open(target)
+            all_dims = [(src.width, src.height)]
+            src.close()
+        except Exception:
+            return jsonify({"conflicts": []})
+
+    # Pas de format sélectionné → conserver le format d'origine
+    if not formats:
+        formats = [src_ext]
+
     conflicts = []
     for fmt in formats:
         for w, h in all_dims:
@@ -764,8 +779,14 @@ def resize_image():
             pass
 
     all_dims = square_dims + custom_dims
-    if not all_dims or not formats:
-        return jsonify({"error": "Aucune dimension ou format valide"}), 400
+
+    # Pas de dimensions sélectionnées → conserver celles d'origine
+    if not all_dims:
+        all_dims = [(max_w, max_h)]
+
+    # Pas de format sélectionné → conserver le format d'origine
+    if not formats:
+        formats = [ext.lstrip(".")]
 
     conflict = request.form.get("conflict", "skip")
     if conflict not in ("backup", "overwrite", "rename", "skip"):
@@ -842,6 +863,9 @@ def resize_image():
 
                 else:
                     img = Image.open(target)
+                    # LANCZOS ne supporte pas le mode palette (ICO, GIF…)
+                    if img.mode not in ("RGB", "RGBA", "L", "LA", "I", "F"):
+                        img = img.convert("RGBA")
                     img = img.resize((w, h), Image.LANCZOS)
                     if fmt == "png":
                         if img.mode not in ("RGBA", "RGB", "L"):
diff --git a/app/templates/preview_image.html b/app/templates/preview_image.html
index 919ba87..63282da 100644
--- a/app/templates/preview_image.html
+++ b/app/templates/preview_image.html
@@ -143,7 +143,7 @@
     {% endif %}
 
     <div class="resize-actions">
-      <button id="resize-btn" class="btn btn-primary" disabled>Générer les copies</button>
+      <button id="resize-btn" class="btn btn-primary">Générer la copie</button>
       <span class="resize-hint">Les fichiers sont créés dans le même dossier</span>
     </div>
 
@@ -261,19 +261,27 @@
     return `${w}x${h}`;
   }
 
-  function canSubmit() {
-    const hasSizes = Array.from(szCbs).some(c => c.checked) || getCustomDim() !== null;
-    const hasFmts  = Array.from(fmtCbs).some(c => c.checked);
-    return hasSizes && hasFmts;
+  function countCopies() {
+    const nSizes = Array.from(szCbs).filter(c => c.checked).length
+                 + (getCustomDim() ? 1 : 0)
+                 || 1;  // 0 sélectionné → dimensions d'origine conservées
+    const nFmts  = Array.from(fmtCbs).filter(c => c.checked).length || 1;
+    return nSizes * nFmts;
+  }
+
+  function btnLabel() {
+    const n = countCopies();
+    return n === 1 ? 'Générer la copie' : `Générer les ${n} copies`;
   }
 
   function updateBtn() {
-    btn.disabled = !canSubmit();
+    btn.textContent = btnLabel();
     conflictPanel.style.display = 'none';
     resizeResolved = false;
   }
 
   [...szCbs, ...fmtCbs].forEach(c => c.addEventListener('change', updateBtn));
+  updateBtn();
 
   function appendDims(fd) {
     szCbs.forEach(c  => { if (c.checked) fd.append('sizes',   c.value); });
@@ -318,8 +326,8 @@
       result.innerHTML = '<p class="resize-err-title">Erreur réseau.</p>';
     }
     result.style.display = 'block';
-    btn.textContent = 'Générer les copies';
-    btn.disabled = !canSubmit();
+    btn.textContent = btnLabel();
+    btn.disabled = false;
     resizeResolved = false;
   }