From 1de79246946458546de2364d4a411f45d27a45cc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adri=C3=A0=20Arrufat?=
 <1671644+arrufat@users.noreply.github.com>
Date: Sun, 29 May 2022 23:53:01 +0900
Subject: [PATCH] Fix saving grayscale WebP images (#2591)

---
 dlib/image_saver/save_webp.h | 4 +++-
 docs/docs/release_notes.xml  | 1 +
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/dlib/image_saver/save_webp.h b/dlib/image_saver/save_webp.h
index fe736179a..e5c00a716 100644
--- a/dlib/image_saver/save_webp.h
+++ b/dlib/image_saver/save_webp.h
@@ -76,7 +76,7 @@ namespace dlib
         auto data = reinterpret_cast<const uint8_t*>(image_data(img));
         const int width = img.nc();
         const int height = img.nr();
-        const int stride = width_step(img);
+        int stride = width_step(img);
         if (pixel_traits<pixel_type>::rgb_alpha)
         {
             if (pixel_traits<pixel_type>::bgr_layout)
@@ -94,8 +94,10 @@ namespace dlib
         else
         {
             // This is some other kind of color image so just save it as an RGB image.
+            // We also need to recompute the stride in case we were given a grayscale image.
             array2d<rgb_pixel> temp;
             assign_image(temp, img);
+            stride = width_step(temp);
             auto data = reinterpret_cast<const uint8_t*>(image_data(temp));
             impl::impl_save_webp(filename, data, width, height, stride, quality, impl::webp_type::rgb);
         }
diff --git a/docs/docs/release_notes.xml b/docs/docs/release_notes.xml
index 6c6bcace4..b8ca7bc97 100644
--- a/docs/docs/release_notes.xml
+++ b/docs/docs/release_notes.xml
@@ -16,6 +16,7 @@ New Features and Improvements:
 Non-Backwards Compatible Changes:
 
 Bug fixes:
+   - Fix saving grayscale WebP images (PR #2591)
 </current>
 
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