[FFmpeg-devel] [PATCH 2/2] avfilter/delogo: change delogo round area to superellipse area

[Jörg Habenicht]

Changed the delogo area to a definition of a superellipse. See here
https://en.wikipedia.org/wiki/Superellipse
Changed the meaning of the parameter 'r'.
'r' = 0.0 resolves to a rectangular area.
0 <'r' < 1 resolves to a star with concave sides.
'r' = 1.0 resolves to a rhombus.
1 < 'r' < 2 resolves to a rhombus with convex sides.
'r' = 2.0 resolves to an ellipse or a circel.
2 < 'r' resolves to something like a rectangle with round corners.
Unset is the default of 'r' = 0.0 .

Signed-off-by: Jörg Habenicht <j.habenicht at gmx.de>
---
 libavfilter/vf_delogo.c | 51 ++++++++++++++++++++++++++++++++++-------
 1 file changed, 43 insertions(+), 8 deletions(-)

diff --git a/libavfilter/vf_delogo.c b/libavfilter/vf_delogo.c
index 60f16b309c..ed81d112e2 100644
--- a/libavfilter/vf_delogo.c
+++ b/libavfilter/vf_delogo.c
@@ -90,7 +90,7 @@ static int set_expr(AVExpr **pexpr, const char *expr, const char *option, void *
  * @param logo_w width of the logo
  * @param logo_h height of the logo
  * @param band   the size of the band around the processed area
- * @param round  whether delogo is applied to a rectangular or round area
+ * @param round  parameter of superellipse, 0==rectanglar, 1.0==rhombus, 2.0==circular/ellipse
  * @param show   show a rectangle around the processed area, useful for
  *               parameters tweaking
  * @param direct if non-zero perform in-place processing
@@ -99,7 +99,7 @@ static void apply_delogo(uint8_t *dst, int dst_linesize,
                          uint8_t *src, int src_linesize,
                          int w, int h, AVRational sar,
                          int logo_x, int logo_y, int logo_w, int logo_h,
-                         unsigned int band, int round, int show, int direct)
+                         unsigned int band, double round, int show, int direct)
 {
     /* Round area algorithm description:
      *
@@ -123,6 +123,18 @@ static void apply_delogo(uint8_t *dst, int dst_linesize,
      *
      * px is later defined x, py defined y.
      * logo_w is later defined logo_w2, logo_h defined logo_h2.
+     *
+     * A point inside a superellipse is defined as x^n / a^n + y^n / b^n = 1
+     * <=> (x + logo_x)^n / (logo_w / 2)^n
+     *     + (y + logo_y)^n / (logo_h / 2)^n <= 1
+     * <=> (px - logo_x - a + logo_x)^n / (logo_w / 2)^n
+     *     + (py - logo_y - b + logo_y)^n / (logo_h / 2)^n <= 1
+     * <=> (px - a)^n / (logo_w / 2)^n
+     *     + (py - b)^n / (logo_h / 2)^n <= 1
+     * <=> ((px - a) / (logo_w / 2))^n
+     *     + ((py - b) / (logo_h / 2))^n <= 1
+     *
+     * n is defined by the parameter 'round'
      */

     int x, y;
@@ -149,7 +161,7 @@ static void apply_delogo(uint8_t *dst, int dst_linesize,
     topright = src+logo_y1 * src_linesize+logo_x2;
     botleft  = src+logo_y2 * src_linesize+logo_x1;

-    if (round) {
+    if (round > 0.0) {
         logo_w2 = (logo_x2 - logo_x1) / 2.0;
         logo_h2 = (logo_y2 - logo_y1) / 2.0;
         a = logo_x1 + logo_w2;
@@ -180,17 +192,40 @@ static void apply_delogo(uint8_t *dst, int dst_linesize,
                 continue;
             }

-            if (round) {
+            if (round > 0.0) {
                 double xf, yf;
                 /* Evaluate if x,y is inside the ellipse, else continue
                  * This is the calculation
-                 *      (px - a)^2 / (logo_w / 2)^2 +
-                 *      (py - b)^2 / (logo_h / 2)^2 <= 1
+                 *      (px - a)^n / (logo_w / 2)^n +
+                 *      (py - b)^n / (logo_h / 2)^n <= 1
                  */
+                errno = 0;
                 xf = ((double)x - a) / logo_w2;
-                xf *= xf;
+                xf = fabs(xf); // use positive values only, analog to xf^2
+                xf = pow(xf, round);
+                if (isnan(xf)) {
+                    av_log(NULL, AV_LOG_ERROR,
+                           "Error in delogo calculating ellipse value. NAN value returned\n");
+                    return;
+                }
+                if (errno) {
+                    av_log(NULL, AV_LOG_ERROR,
+                           "Error in delogo calculating ellipse value. Math error returned\n");
+                    return;
+                }
                 yf = ((double)y - b) / logo_h2;
-                yf *= yf;
+                yf = fabs(yf); // use positive values only, analog to yf^2
+                yf = pow(yf, round);
+                if (isnan(xf)) {
+                    av_log(NULL, AV_LOG_ERROR,
+                           "Error in delogo calculating ellipse value. NAN value returned\n");
+                    return;
+                }
+                if (errno) {
+                    av_log(NULL, AV_LOG_ERROR,
+                           "Error in delogo calculating ellipse value. Math error returned\n");
+                    return;
+                }
                 if (xf + yf > 1.0)
                     continue;
             }
--
2.45.3