Make image-quality more consistent

src/blob.rs

@@ -12,7 +12,7 @@ use futures::StreamExt;
 use image::ImageReader;
 use image::codecs::jpeg::JpegEncoder;
 use image::{DynamicImage, GenericImage, GenericImageView, ImageFormat, Pixel, Rgba};
-use num_traits::FromPrimitive;
+use num_traits::{FromPrimitive, cast};
 use tokio::{fs, task};
 use tokio_stream::wrappers::ReadDirStream;
 
@@ -388,14 +388,9 @@ impl<'a> BlobObject<'a> {
                 _ => img,
             };
 
-            // max_wh is the maximum image width and height, i.e. the resolution-limit.
-            // target_wh target-resolution for resizing the image.
+            // max_wh is the maximum image width and height, i.e. the resolution-limit,
+            // as set by `Config::MediaQuality`.
             let exceeds_wh = img.width() > max_wh || img.height() > max_wh;
-            let mut target_wh = if exceeds_wh {
-                max_wh
-            } else {
-                max(img.width(), img.height())
-            };
             let exceeds_max_bytes = nr_bytes > max_bytes as u64;
 
             let jpeg_quality = 75;
@@ -434,6 +429,35 @@ impl<'a> BlobObject<'a> {
                         });
 
             if do_scale {
+                let n_px_longest_side = max(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();
+                    // 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 limit: Option<u32> = cast(
+                        (f64::from(n_px_longest_side) * (f64::from(max_wh) / n_all_px_sqrt))
+                            .floor(),
+                    );
+                    let mut resolution_limit = limit.context("resolution_limit is out of range")?;
+                    // Align at least one dimension of the resampled image to a multiple of 8 pixels,
+                    // to have fewer partially used JPEG-blocks (which represent 8x8 pixels each).
+                    if resolution_limit < n_px_longest_side {
+                        while !resolution_limit.is_multiple_of(8) {
+                            resolution_limit -= 1
+                        }
+                    }
+                    resolution_limit
+                } else {
+                    max_wh
+                };
+
+                if target_wh > n_px_longest_side {
+                    target_wh = n_px_longest_side;
+                };
+
                 loop {
                     if mem::take(&mut add_white_bg) {
                         self::add_white_bg(&mut img);

src/blob/blob_tests.rs

@@ -384,8 +384,8 @@ async fn test_recode_image_balanced_png() {
         extension: "png",
         original_width: 1920,
         original_height: 1080,
-        compressed_width: constants::WORSE_IMAGE_SIZE,
-        compressed_height: constants::WORSE_IMAGE_SIZE * 1080 / 1920,
+        compressed_width: 848,
+        compressed_height: 477,
         ..Default::default()
     }
     .test()
@@ -475,8 +475,8 @@ async fn test_recode_image_rgba_png_to_jpeg() {
         extension: "png",
         original_width: 1920,
         original_height: 1080,
-        compressed_width: constants::WORSE_IMAGE_SIZE,
-        compressed_height: constants::WORSE_IMAGE_SIZE * 1080 / 1920,
+        compressed_width: 848,
+        compressed_height: 477,
         ..Default::default()
     }
     .test()
@@ -495,8 +495,8 @@ async fn test_recode_image_huge_jpg() {
         has_exif: true,
         original_width: 1920,
         original_height: 1080,
-        compressed_width: constants::BALANCED_IMAGE_SIZE,
-        compressed_height: constants::BALANCED_IMAGE_SIZE * 1080 / 1920,
+        compressed_width: 1704,
+        compressed_height: 959,
         ..Default::default()
     }
     .test()

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 – 146.12 KiB]".to_owned());
+    assert_eq!(msg.get_text(), "test [Image – 228.45 KiB]".to_owned());
 
     Ok(())
 }

src/tests/pre_messages/receiving.rs

@@ -323,9 +323,9 @@ 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(149632));
-    assert_eq!(msg.get_height(), 1280);
-    assert_eq!(msg.get_width(), 720);
+    assert_eq!(msg.get_filebytes(bob).await?, Some(233935));
+    assert_eq!(msg.get_height(), 1704);
+    assert_eq!(msg.get_width(), 959);
 
     Ok(())
 }