feat: better avatar quality (#6822)

this PR scaled avatars using the Triangle-filter,
resulting in often better image quality and smaller files (5%).

it comes at high costs,
therefore, we do not do that unconditionally for each image sent, see
comment in the code
and https://github.com/chatmail/core/pull/6815

---------

Co-authored-by: iequidoo <117991069+iequidoo@users.noreply.github.com>

src/blob.rs

@@ -432,7 +432,20 @@ impl<'a> BlobObject<'a> {
                     if mem::take(&mut add_white_bg) {
                         self::add_white_bg(&mut img);
                     }
-                    let new_img = img.thumbnail(img_wh, img_wh);
+
+                    // resize() results in often slightly better quality,
+                    // however, comes at high price of being 4+ times slower than thumbnail().
+                    // for a typical camera image that is sent, this may be a change from "instant" (500ms) to "long time waiting" (3s).
+                    // as we do not have recoding in background while chat has already a preview,
+                    // we vote for speed.
+                    // exception is the avatar image: this is far more often sent than recoded,
+                    // usually has less pixels by cropping, UI that needs to wait anyways,
+                    // and also benefits from slightly better (5%) encoding of Triangle-filtered images.
+                    let new_img = if is_avatar {
+                        img.resize(img_wh, img_wh, image::imageops::FilterType::Triangle)
+                    } else {
+                        img.thumbnail(img_wh, img_wh)
+                    };
 
                     if encoded_img_exceeds_bytes(
                         context,

src/blob/blob_tests.rs

@@ -174,7 +174,7 @@ async fn test_selfavatar_outside_blobdir() {
     let avatar_blob = t.get_config(Config::Selfavatar).await.unwrap().unwrap();
     let avatar_path = Path::new(&avatar_blob);
     assert!(
-        avatar_blob.ends_with("1e08d1c9398297c21dd3820f7db2324.jpg"),
+        avatar_blob.ends_with("7dde69e06b5ae6c27520a436bbfd65b.jpg"),
         "The avatar filename should be its hash, put instead it's {avatar_blob}"
     );
     let scaled_avatar_size = file_size(avatar_path).await;
@@ -226,7 +226,7 @@ async fn test_selfavatar_in_blobdir() {
         .unwrap();
     let avatar_cfg = t.get_config(Config::Selfavatar).await.unwrap().unwrap();
     assert!(
-        avatar_cfg.ends_with("ec054c444a5755adf2b0aaea40209f2.png"),
+        avatar_cfg.ends_with("d57cb5ce5f371531b6e1fb17b6dd1af.png"),
         "Avatar file name {avatar_cfg} should end with its hash"
     );