From e79d1746f29412c069d30770d86616aa3dafb1d4 Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Tue, 26 Mar 2024 19:57:17 +1100
Subject: [PATCH] Support conversion from RGB to La

---
 Tests/test_image_convert.py | 4 ++++
 src/PIL/Image.py            | 2 +-
 src/libImaging/Convert.c    | 8 ++++++--
 3 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/Tests/test_image_convert.py b/Tests/test_image_convert.py
index 77ce4e7d5..2fb45854a 100644
--- a/Tests/test_image_convert.py
+++ b/Tests/test_image_convert.py
@@ -187,6 +187,10 @@ def test_trns_RGB(tmp_path: Path) -> None:
     assert "transparency" not in im_la.info
     im_la.save(f)
 
+    im_la = im.convert("La")
+    assert "transparency" not in im_la.info
+    assert im_la.getpixel((0, 0)) == (0, 0)
+
     im_p = im.convert("P")
     assert "transparency" in im_p.info
     im_p.save(f)
diff --git a/src/PIL/Image.py b/src/PIL/Image.py
index 11a3459ed..5c2309ac3 100644
--- a/src/PIL/Image.py
+++ b/src/PIL/Image.py
@@ -979,7 +979,7 @@ class Image:
         # transparency handling
         if has_transparency:
             if (self.mode in ("1", "L", "I", "I;16") and mode in ("LA", "RGBA")) or (
-                self.mode == "RGB" and mode in ("LA", "RGBa", "RGBA")
+                self.mode == "RGB" and mode in ("La", "LA", "RGBa", "RGBA")
             ):
                 # Use transparent conversion to promote from transparent
                 # color to an alpha channel.
diff --git a/src/libImaging/Convert.c b/src/libImaging/Convert.c
index 4db9eb700..0b84aa1ba 100644
--- a/src/libImaging/Convert.c
+++ b/src/libImaging/Convert.c
@@ -501,7 +501,7 @@ rgba2rgb_(UINT8 *out, const UINT8 *in, int xsize) {
 /*
  * Conversion of RGB + single transparent color either to
  * RGBA or LA, where any pixel matching the color will have the alpha channel set to 0, or
- * RGBa, where any pixel matching the color will have all channels set to 0
+ * RGBa or La, where any pixel matching the color will have all channels set to 0
  */
 
 static void
@@ -942,6 +942,7 @@ static struct {
     {"RGB", "1", rgb2bit},
     {"RGB", "L", rgb2l},
     {"RGB", "LA", rgb2la},
+    {"RGB", "La", rgb2la},
     {"RGB", "I", rgb2i},
     {"RGB", "F", rgb2f},
     {"RGB", "BGR;15", rgb2bgr15},
@@ -1698,9 +1699,12 @@ ImagingConvertTransparent(Imaging imIn, const char *mode, int r, int g, int b) {
         if (strcmp(mode, "RGBa") == 0) {
             premultiplied = 1;
         }
-    } else if (strcmp(imIn->mode, "RGB") == 0 && strcmp(mode, "LA") == 0) {
+    } else if (strcmp(imIn->mode, "RGB") == 0 && (strcmp(mode, "LA") == 0 || strcmp(mode, "La") == 0)) {
         convert = rgb2la;
         source_transparency = 1;
+        if (strcmp(mode, "La") == 0) {
+            premultiplied = 1;
+        }
     } else if ((strcmp(imIn->mode, "1") == 0 ||
                 strcmp(imIn->mode, "I") == 0 ||
                 strcmp(imIn->mode, "I;16") == 0 ||