diff --git a/index.html b/index.html
index 736f55a..0862b2e 100644
--- a/index.html
+++ b/index.html
@@ -853,7 +853,20 @@ uploadBtn.addEventListener('click', () => {
 
 uploadAnyInput.addEventListener('change', e => {
   const file = e.target.files[0];
-  if (file) processFile(file);
+  if (!file) return;
+  if (outputSection.style.display && outputSection.style.display !== 'none') {
+    const name = file.name.toLowerCase();
+    const isDataFormat = name.endsWith('.fit') || name.endsWith('.fits') ||
+                         name.endsWith('.cr2') || name.endsWith('.cr3') ||
+                         name.endsWith('.tif') || name.endsWith('.tiff');
+    if (isDataFormat) {
+      processFile(file);
+    } else {
+      swapBackground(file);
+    }
+  } else {
+    processFile(file);
+  }
   uploadAnyInput.value = '';
 });