avfilter/interlace: add complex vertical low-pass filter

This complex (-1 2 6 2 -1) filter slightly less reduces interlace 'twitter' but better retain detail and subjective sharpness impression compared to the linear (1 2 1) filter.

Signed-off-by: Thomas Mundt <tmundt75@gmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>

1 files changed, 50 insertions, 11 deletions

diff --git a/libavfilter/vf_tinterlace.c b/libavfilter/vf_tinterlace.c
index 09ca4d30ee..65997076ad 100644
--- a/libavfilter/vf_tinterlace.c
+++ b/libavfilter/vf_tinterlace.c
@@ -1,4 +1,5 @@
 /*
+ * Copyright (c) 2017 Thomas Mundt <tmundt75@gmail.com>
  * Copyright (c) 2011 Stefano Sabatini
  * Copyright (c) 2010 Baptiste Coudurier
  * Copyright (c) 2003 Michael Zucchi <notzed@ximian.com>
@@ -34,8 +35,6 @@
 
 #define OFFSET(x) offsetof(TInterlaceContext, x)
 #define FLAGS AV_OPT_FLAG_FILTERING_PARAM|AV_OPT_FLAG_VIDEO_PARAM
-#define TINTERLACE_FLAG_VLPF 01
-#define TINTERLACE_FLAG_EXACT_TB 2
 
 static const AVOption tinterlace_options[] = {
     {"mode",              "select interlace mode", OFFSET(mode), AV_OPT_TYPE_INT, {.i64=MODE_MERGE}, 0, MODE_NB-1, FLAGS, "mode"},
@@ -51,6 +50,8 @@ static const AVOption tinterlace_options[] = {
     {"flags",             "set flags", OFFSET(flags), AV_OPT_TYPE_FLAGS, {.i64 = 0}, 0, INT_MAX, 0, "flags" },
     {"low_pass_filter",   "enable vertical low-pass filter",              0, AV_OPT_TYPE_CONST, {.i64 = TINTERLACE_FLAG_VLPF}, INT_MIN, INT_MAX, FLAGS, "flags" },
     {"vlpf",              "enable vertical low-pass filter",              0, AV_OPT_TYPE_CONST, {.i64 = TINTERLACE_FLAG_VLPF}, INT_MIN, INT_MAX, FLAGS, "flags" },
+    {"complex_filter",    "enable complex vertical low-pass filter",      0, AV_OPT_TYPE_CONST, {.i64 = TINTERLACE_FLAG_CVLPF},INT_MIN, INT_MAX, FLAGS, "flags" },
+    {"cvlpf",             "enable complex vertical low-pass filter",      0, AV_OPT_TYPE_CONST, {.i64 = TINTERLACE_FLAG_CVLPF},INT_MIN, INT_MAX, FLAGS, "flags" },
     {"exact_tb",          "force a timebase which can represent timestamps exactly", 0, AV_OPT_TYPE_CONST, {.i64 = TINTERLACE_FLAG_EXACT_TB}, INT_MIN, INT_MAX, FLAGS, "flags" },
 
     {NULL}
@@ -102,6 +103,24 @@ static void lowpass_line_c(uint8_t *dstp, ptrdiff_t width, const uint8_t *srcp,
     }
 }
 
+static void lowpass_line_complex_c(uint8_t *dstp, ptrdiff_t width, const uint8_t *srcp,
+                                   ptrdiff_t mref, ptrdiff_t pref)
+{
+    const uint8_t *srcp_above = srcp + mref;
+    const uint8_t *srcp_below = srcp + pref;
+    const uint8_t *srcp_above2 = srcp + mref * 2;
+    const uint8_t *srcp_below2 = srcp + pref * 2;
+    int i;
+    for (i = 0; i < width; i++) {
+        // this calculation is an integer representation of
+        // '0.75 * current + 0.25 * above + 0.25 * below - 0.125 * above2 - 0.125 * below2'
+        // '4 +' is for rounding.
+        dstp[i] = av_clip_uint8((4 + (srcp[i] << 2)
+                  + ((srcp[i] + srcp_above[i] + srcp_below[i]) << 1)
+                  - srcp_above2[i] - srcp_below2[i]) >> 3);
+    }
+}
+
 static av_cold void uninit(AVFilterContext *ctx)
 {
     TInterlaceContext *tinterlace = ctx->priv;
@@ -144,12 +163,14 @@ static int config_out_props(AVFilterLink *outlink)
                    tinterlace->black_linesize[i] * h);
         }
     }
-    if ((tinterlace->flags & TINTERLACE_FLAG_VLPF)
+    if ((tinterlace->flags & TINTERLACE_FLAG_VLPF
+          || tinterlace->flags & TINTERLACE_FLAG_CVLPF)
             && !(tinterlace->mode == MODE_INTERLEAVE_TOP
               || tinterlace->mode == MODE_INTERLEAVE_BOTTOM)) {
-        av_log(ctx, AV_LOG_WARNING, "low_pass_filter flag ignored with mode %d\n",
+        av_log(ctx, AV_LOG_WARNING, "low_pass_filter flags ignored with mode %d\n",
                 tinterlace->mode);
         tinterlace->flags &= ~TINTERLACE_FLAG_VLPF;
+        tinterlace->flags &= ~TINTERLACE_FLAG_CVLPF;
     }
     tinterlace->preout_time_base = inlink->time_base;
     if (tinterlace->mode == MODE_INTERLACEX2) {
@@ -172,14 +193,19 @@ static int config_out_props(AVFilterLink *outlink)
         (tinterlace->flags & TINTERLACE_FLAG_EXACT_TB))
         outlink->time_base = tinterlace->preout_time_base;
 
-    if (tinterlace->flags & TINTERLACE_FLAG_VLPF) {
+    if (tinterlace->flags & TINTERLACE_FLAG_CVLPF) {
+        tinterlace->lowpass_line = lowpass_line_complex_c;
+        if (ARCH_X86)
+            ff_tinterlace_init_x86(tinterlace);
+    } else if (tinterlace->flags & TINTERLACE_FLAG_VLPF) {
         tinterlace->lowpass_line = lowpass_line_c;
         if (ARCH_X86)
             ff_tinterlace_init_x86(tinterlace);
     }
 
-    av_log(ctx, AV_LOG_VERBOSE, "mode:%d filter:%s h:%d -> h:%d\n",
-           tinterlace->mode, (tinterlace->flags & TINTERLACE_FLAG_VLPF) ? "on" : "off",
+    av_log(ctx, AV_LOG_VERBOSE, "mode:%d filter:%s h:%d -> h:%d\n", tinterlace->mode,
+           (tinterlace->flags & TINTERLACE_FLAG_CVLPF) ? "complex" :
+           (tinterlace->flags & TINTERLACE_FLAG_VLPF) ? "linear" : "off",
            inlink->h, outlink->h);
 
     return 0;
@@ -223,10 +249,23 @@ void copy_picture_field(TInterlaceContext *tinterlace,
             srcp += src_linesize[plane];
         if (interleave && dst_field == FIELD_LOWER)
             dstp += dst_linesize[plane];
-        if (flags & TINTERLACE_FLAG_VLPF) {
-            // Low-pass filtering is required when creating an interlaced destination from
-            // a progressive source which contains high-frequency vertical detail.
-            // Filtering will reduce interlace 'twitter' and Moire patterning.
+        // Low-pass filtering is required when creating an interlaced destination from
+        // a progressive source which contains high-frequency vertical detail.
+        // Filtering will reduce interlace 'twitter' and Moire patterning.
+        if (flags & TINTERLACE_FLAG_CVLPF) {
+            int srcp_linesize = src_linesize[plane] * k;
+            int dstp_linesize = dst_linesize[plane] * (interleave ? 2 : 1);
+            for (h = lines; h > 0; h--) {
+                ptrdiff_t pref = src_linesize[plane];
+                ptrdiff_t mref = -pref;
+                if (h >= (lines - 1)) mref = 0;
+                else if (h <= 2)      pref = 0;
+
+                tinterlace->lowpass_line(dstp, cols, srcp, mref, pref);
+                dstp += dstp_linesize;
+                srcp += srcp_linesize;
+            }
+        } else if (flags & TINTERLACE_FLAG_VLPF) {
             int srcp_linesize = src_linesize[plane] * k;
             int dstp_linesize = dst_linesize[plane] * (interleave ? 2 : 1);
             for (h = lines; h > 0; h--) {