convert_to: support for RGBa -> BGR.

Author: bigcat88

pillow_heif/helpers.c

@@ -503,6 +503,25 @@ void convert_rgba_premultiplied_to_rgb(const uint8_t *in, int in_stride, uint8_t
     }
 }
 
+void convert_rgba_premultiplied_to_bgr(const uint8_t *in, int in_stride, uint8_t *out, int out_stride, int n_rows)
+{
+    const uint32_t* in_row = (uint32_t*)in;
+    uint8_t* out_row = out;
+    in_stride = in_stride / 4;
+    int stride_elements = out_stride / 3 > in_stride ? in_stride : out_stride / 3;
+    for (int i = 0; i < n_rows; i++) {
+        for (int i2 = 0; i2 < stride_elements; i2++) {
+            uint32_t p = in_row[i2];
+            uint8_t a =  (p >> 24) & 0xFF;
+            out_row[i2 * 3 + 0] = (((p >> 16) & 0xFF) * a) / 255;
+            out_row[i2 * 3 + 1] = (((p >> 8) & 0xFF) * a) / 255;
+            out_row[i2 * 3 + 2] = (((p >> 0) & 0xFF) * a) / 255;
+        }
+        in_row += in_stride;
+        out_row += out_stride;
+    }
+}
+
 #ifdef __cplusplus
     }
 #endif

pillow_heif/helpers.h

@@ -51,3 +51,5 @@ void convert_bgra_rgba(const uint8_t *in, int in_stride, uint8_t *out, int out_s
 void convert_bgr_rgb(const uint8_t *in, int in_stride, uint8_t *out, int out_stride, int n_rows);
 
 void convert_rgba_premultiplied_to_rgb(const uint8_t *in, int in_stride, uint8_t *out, int out_stride, int n_rows);
+
+void convert_rgba_premultiplied_to_bgr(const uint8_t *in, int in_stride, uint8_t *out, int out_stride, int n_rows);

pillow_heif/private.py

@@ -72,6 +72,7 @@ def get_pure_stride(mode: str, width: int):
         "RGBa;16": lib.convert_rgba_to_rgba16,
         "BGRa;16": lib.convert_rgba_to_bgra16,
         "RGB": lib.convert_rgba_premultiplied_to_rgb,
+        "BGR": lib.convert_rgba_premultiplied_to_bgr,
     },
     "RGB": {"BGR": lib.convert_bgr_rgb, "RGB;16": lib.convert_rgb_to_rgb16, "BGR;16": lib.convert_rgb_to_bgr16},
 }

tests/mode_convert_test.py

@@ -132,3 +132,20 @@ def test_rgba_premultiplied_to_rgb():
         "f3e3e3f3d423f40413f40413f3f403f3f403f3e3f3f3e3f3f3d3e3f3d423f40423f3f413f3f41"
         "3f3e403f3e403f3d3f3f3d3f3f3c433f3f423f3f423f3e413f3e413f3d403f3d403f3c3f3f3c"
     )
+
+
+def test_rgba_premultiplied_to_bgr():
+    im_heif = from_pillow(helpers.gradient_rgba().crop((124, 124, 132, 132)))
+    im_heif.premultiplied_alpha = True
+    assert im_heif.mode == "RGBa"
+    im_heif.convert_to("BGR")
+    assert im_heif.mode == "BGR"
+    im_heif.convert_to("RGB")
+    assert (
+        im_heif.to_pillow().tobytes().hex()
+        == "3f3f433f3f423e3f423e3f413d3f413d3f403c3f403c3f3f403f423f3f423f3f413e3f413e3f4"
+        "03d3f403d3f3f3c3f3f403f42403f413f3f413f3f403e3f403e3f3f3d3f3f3d3f3e413f41403f"
+        "41403f403f3f403f3f3f3e3f3f3e3f3e3d3f3e413f41413f40403f40403f3f3f3f3f3f3f3e3e3"
+        "f3e3e3f3d423f40413f40413f3f403f3f403f3e3f3f3e3f3f3d3e3f3d423f40423f3f413f3f41"
+        "3f3e403f3e403f3d3f3f3d3f3f3c433f3f423f3f423f3e413f3e413f3d403f3d403f3c3f3f3c"
+    )