feat: Use resize when resampling images with up to 2.56 megapixels

Author: 72374

src/blob.rs

@@ -430,11 +430,12 @@ impl<'a> BlobObject<'a> {
 
             if do_scale {
                 let n_px_longest_side = max(img.width(), img.height());
+                let n_all_px = img.width() * img.height();
 
                 // target_wh will be used as the target-resolution for resizing the image,
                 // so that the longest sides of the image match the target-resolution.
                 let mut target_wh = if !is_avatar {
-                    let n_all_px_sqrt = f64::from(img.width() * img.height()).sqrt();
+                    let n_all_px_sqrt = f64::from(n_all_px).sqrt();
                     // Limit resolution to the number of pixels that fit within max_wh * max_wh,
                     // so that the image-quality does not depend on the aspect-ratio.
                     let mut resolution_limit =
@@ -460,15 +461,13 @@ impl<'a> BlobObject<'a> {
                         self::add_white_bg(&mut img);
                     }
 
-                    // 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 {
+                    // resize() results in better quality than thumbnail(),
+                    // however, comes at the price of being 4+ times slower than thumbnail().
+                    // For a typical camera-image that is sent (often more than 8 megapixels),
+                    // this may be a change from "instant" (500ms) to "long time waiting" (3s).
+                    // As we do not have recoding in the background while the chat already has a preview,
+                    // we vote for speed, if the original image has a high resolution (> 2.56 megapixels).
+                    let new_img = if is_avatar || n_all_px <= 1600 * 1600 {
                         img.resize(target_wh, target_wh, image::imageops::FilterType::Triangle)
                     } else {
                         img.thumbnail(target_wh, target_wh)

src/tests/pre_messages/additional_text.rs

@@ -34,7 +34,7 @@ async fn test_additional_text_on_different_viewtypes() -> Result<()> {
     let (pre_message, _, _) = send_large_image_message(alice, a_group_id).await?;
     let msg = bob.recv_msg(&pre_message).await;
     assert_eq!(msg.text, "test".to_owned());
-    assert_eq!(msg.get_text(), "test [Image – 228.45 KiB]".to_owned());
+    assert_eq!(msg.get_text(), "test [Image – 210.38 KiB]".to_owned());
 
     Ok(())
 }

src/tests/pre_messages/receiving.rs

@@ -323,7 +323,7 @@ async fn test_receive_pre_message_image() -> Result<()> {
     // test that metadata is correctly returned by methods
     assert_eq!(msg.get_post_message_viewtype(), Some(Viewtype::Image));
     // recoded image dimensions
-    assert_eq!(msg.get_filebytes(bob).await?, Some(233935));
+    assert_eq!(msg.get_filebytes(bob).await?, Some(215424));
     assert_eq!(msg.get_height(), 1704);
     assert_eq!(msg.get_width(), 959);