diff --git a/Changelog b/Changelog
index fa443dc22d..0346877b4b 100644
--- a/Changelog
+++ b/Changelog
@@ -29,6 +29,7 @@ version <next>:
 - showcqt multimedia filter
 - zoompan filter
 - signalstats filter
+- hqx filter (hq2x, hq3x, hq4x)
 
 
 version 2.2:
diff --git a/MAINTAINERS b/MAINTAINERS
index 67be174f50..d06030bb2b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -350,6 +350,7 @@ Filters:
   vf_drawbox.c/drawgrid                 Andrey Utkin
   vf_extractplanes.c                    Paul B Mahol
   vf_histogram.c                        Paul B Mahol
+  vf_hqx.c                              Clément Bœsch
   vf_il.c                               Paul B Mahol
   vf_mergeplanes.c                      Paul B Mahol
   vf_psnr.c                             Paul B Mahol
diff --git a/doc/filters.texi b/doc/filters.texi
index 63bd22e760..a5f6965948 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -5203,6 +5203,20 @@ A floating point number which specifies chroma temporal strength. It defaults to
 @var{luma_tmp}*@var{chroma_spatial}/@var{luma_spatial}.
 @end table
 
+@section hqx
+
+Apply a high-quality magnification filter designed for pixel art. This filter
+was originally created by Maxim Stepin.
+
+It accepts the following option:
+
+@table @option
+@item n
+Set the scaling dimension: @code{2} for @code{hq2x}, @code{3} for
+@code{hq3x} and @code{4} for @code{hq4x}.
+Default is @code{3}.
+@end table
+
 @section hue
 
 Modify the hue and/or the saturation of the input.
diff --git a/libavfilter/Makefile b/libavfilter/Makefile
index 5b9fabf89d..08817ee391 100644
--- a/libavfilter/Makefile
+++ b/libavfilter/Makefile
@@ -130,6 +130,7 @@ OBJS-$(CONFIG_HFLIP_FILTER)                  += vf_hflip.o
 OBJS-$(CONFIG_HISTEQ_FILTER)                 += vf_histeq.o
 OBJS-$(CONFIG_HISTOGRAM_FILTER)              += vf_histogram.o
 OBJS-$(CONFIG_HQDN3D_FILTER)                 += vf_hqdn3d.o
+OBJS-$(CONFIG_HQX_FILTER)                    += vf_hqx.o
 OBJS-$(CONFIG_HUE_FILTER)                    += vf_hue.o
 OBJS-$(CONFIG_IDET_FILTER)                   += vf_idet.o
 OBJS-$(CONFIG_IL_FILTER)                     += vf_il.o
diff --git a/libavfilter/allfilters.c b/libavfilter/allfilters.c
index 1e86967be6..e4ac983b54 100644
--- a/libavfilter/allfilters.c
+++ b/libavfilter/allfilters.c
@@ -148,6 +148,7 @@ void avfilter_register_all(void)
     REGISTER_FILTER(HISTEQ,         histeq,         vf);
     REGISTER_FILTER(HISTOGRAM,      histogram,      vf);
     REGISTER_FILTER(HQDN3D,         hqdn3d,         vf);
+    REGISTER_FILTER(HQX,            hqx,            vf);
     REGISTER_FILTER(HUE,            hue,            vf);
     REGISTER_FILTER(IDET,           idet,           vf);
     REGISTER_FILTER(IL,             il,             vf);
diff --git a/libavfilter/version.h b/libavfilter/version.h
index a518e8f6e2..f125032e66 100644
--- a/libavfilter/version.h
+++ b/libavfilter/version.h
@@ -30,7 +30,7 @@
 #include "libavutil/version.h"
 
 #define LIBAVFILTER_VERSION_MAJOR   4
-#define LIBAVFILTER_VERSION_MINOR   8
+#define LIBAVFILTER_VERSION_MINOR   9
 #define LIBAVFILTER_VERSION_MICRO 100
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \
diff --git a/libavfilter/vf_hqx.c b/libavfilter/vf_hqx.c
new file mode 100644
index 0000000000..c4122295b9
--- /dev/null
+++ b/libavfilter/vf_hqx.c
@@ -0,0 +1,560 @@
+/*
+ * Copyright (c) 2014 Clément Bœsch
+ *
+ * This file is part of FFmpeg.
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/**
+ * @file
+ * hqx magnification filters (hq2x, hq3x, hq4x)
+ *
+ * Originally designed by Maxim Stephin.
+ *
+ * @see http://en.wikipedia.org/wiki/Hqx
+ * @see http://web.archive.org/web/20131114143602/http://www.hiend3d.com/hq3x.html
+ */
+
+#include "libavutil/opt.h"
+#include "libavutil/avassert.h"
+#include "libavutil/pixdesc.h"
+#include "internal.h"
+
+typedef int (*hqxfunc_t)(AVFilterContext *ctx, void *arg, int jobnr, int nb_jobs);
+
+typedef struct {
+    const AVClass *class;
+    int n;
+    hqxfunc_t func;
+    uint32_t rgbtoyuv[1<<24];
+} HQXContext;
+
+typedef struct ThreadData {
+    AVFrame *in, *out;
+    const uint32_t *rgbtoyuv;
+} ThreadData;
+
+#define OFFSET(x) offsetof(HQXContext, x)
+#define FLAGS AV_OPT_FLAG_FILTERING_PARAM|AV_OPT_FLAG_VIDEO_PARAM
+static const AVOption hqx_options[] = {
+    { "n", "set scale factor", OFFSET(n), AV_OPT_TYPE_INT, {.i64 = 3}, 2, 4, .flags = FLAGS },
+    { NULL }
+};
+
+AVFILTER_DEFINE_CLASS(hqx);
+
+static av_always_inline uint32_t rgb2yuv(const uint32_t *r2y, uint32_t c)
+{
+    return r2y[c & 0xffffff];
+}
+
+static av_always_inline int yuv_diff(uint32_t yuv1, uint32_t yuv2)
+{
+#define YMASK 0xff0000
+#define UMASK 0x00ff00
+#define VMASK 0x0000ff
+    return abs((yuv1 & YMASK) - (yuv2 & YMASK)) > (48 << 16) ||
+           abs((yuv1 & UMASK) - (yuv2 & UMASK)) > ( 7 <<  8) ||
+           abs((yuv1 & VMASK) - (yuv2 & VMASK)) > ( 6 <<  0);
+}
+
+/* (c1*w1 + c2*w2) >> s */
+static av_always_inline uint32_t interp_2px(uint32_t c1, int w1, uint32_t c2, int w2, int s)
+{
+    return (((((c1 & 0xff00ff00) >> 8) * w1 + ((c2 & 0xff00ff00) >> 8) * w2) << (8 - s)) & 0xff00ff00) |
+           (((((c1 & 0x00ff00ff)     ) * w1 + ((c2 & 0x00ff00ff)     ) * w2) >>      s ) & 0x00ff00ff);
+}
+
+/* (c1*w1 + c2*w2 + c3*w3) >> s */
+static av_always_inline uint32_t interp_3px(uint32_t c1, int w1, uint32_t c2, int w2, uint32_t c3, int w3, int s)
+{
+    return (((((c1 & 0xff00ff00) >> 8) * w1 + ((c2 & 0xff00ff00) >> 8) * w2 + ((c3 & 0xff00ff00) >> 8) * w3) << (8 - s)) & 0xff00ff00) |
+           (((((c1 & 0x00ff00ff)     ) * w1 + ((c2 & 0x00ff00ff)     ) * w2 + ((c3 & 0x00ff00ff)     ) * w3) >>      s ) & 0x00ff00ff);
+}
+
+/* m is the mask of diff with the center pixel that matters in the pattern, and
+ * r is the expected result (bit set to 1 if there is difference with the
+ * center, 0 otherwise) */
+#define P(m, r) ((k_shuffled & (m)) == (r))
+
+/* adjust 012345678 to 01235678: the mask doesn't contain the (null) diff
+ * between the center/current pixel and itself */
+#define DROP4(z) ((z) > 4 ? (z)-1 : (z))
+
+/* shuffle the input mask: move bit n (4-adjusted) to position stored in p<n> */
+#define SHF(x, rot, n) (((x) >> ((rot) ? 7-DROP4(n) : DROP4(n)) & 1) << DROP4(p##n))
+
+/* used to check if there is YUV difference between 2 pixels */
+#define WDIFF(c1, c2) yuv_diff(rgb2yuv(r2y, c1), rgb2yuv(r2y, c2))
+
+/* bootstrap template for every interpolation code. It defines the shuffled
+ * masks and surrounding pixels. The rot flag is used to indicate if it's a
+ * rotation; its basic effect is to shuffle k using p8..p0 instead of p0..p8 */
+#define INTERP_BOOTSTRAP(rot)                                           \
+    const int k_shuffled = SHF(k,rot,0) | SHF(k,rot,1) | SHF(k,rot,2)   \
+                         | SHF(k,rot,3) |       0      | SHF(k,rot,5)   \
+                         | SHF(k,rot,6) | SHF(k,rot,7) | SHF(k,rot,8);  \
+                                                                        \
+    const uint32_t w0 = w[p0], w1 = w[p1],                              \
+                   w3 = w[p3], w4 = w[p4], w5 = w[p5],                  \
+                               w7 = w[p7]
+
+/* Assuming p0..p8 is mapped to pixels 0..8, this function interpolates the
+ * top-left pixel in the total of the 2x2 pixels to interpolates. The function
+ * is also used for the 3 other pixels */
+static av_always_inline uint32_t hq2x_interp_1x1(const uint32_t *r2y, int k,
+                                                 const uint32_t *w,
+                                                 int p0, int p1, int p2,
+                                                 int p3, int p4, int p5,
+                                                 int p6, int p7, int p8)
+{
+    INTERP_BOOTSTRAP(0);
+
+    if ((P(0xbf,0x37) || P(0xdb,0x13)) && WDIFF(w1, w5))
+        return interp_2px(w4, 3, w3, 1, 2);
+    if ((P(0xdb,0x49) || P(0xef,0x6d)) && WDIFF(w7, w3))
+        return interp_2px(w4, 3, w1, 1, 2);
+    if ((P(0x0b,0x0b) || P(0xfe,0x4a) || P(0xfe,0x1a)) && WDIFF(w3, w1))
+        return w4;
+    if ((P(0x6f,0x2a) || P(0x5b,0x0a) || P(0xbf,0x3a) || P(0xdf,0x5a) ||
+         P(0x9f,0x8a) || P(0xcf,0x8a) || P(0xef,0x4e) || P(0x3f,0x0e) ||
+         P(0xfb,0x5a) || P(0xbb,0x8a) || P(0x7f,0x5a) || P(0xaf,0x8a) ||
+         P(0xeb,0x8a)) && WDIFF(w3, w1))
+        return interp_2px(w4, 3, w0, 1, 2);
+    if (P(0x0b,0x08))
+        return interp_3px(w4, 2, w0, 1, w1, 1, 2);
+    if (P(0x0b,0x02))
+        return interp_3px(w4, 2, w0, 1, w3, 1, 2);
+    if (P(0x2f,0x2f))
+        return interp_3px(w4, 14, w3, 1, w1, 1, 4);
+    if (P(0xbf,0x37) || P(0xdb,0x13))
+        return interp_3px(w4, 5, w1, 2, w3, 1, 3);
+    if (P(0xdb,0x49) || P(0xef,0x6d))
+        return interp_3px(w4, 5, w3, 2, w1, 1, 3);
+    if (P(0x1b,0x03) || P(0x4f,0x43) || P(0x8b,0x83) || P(0x6b,0x43))
+        return interp_2px(w4, 3, w3, 1, 2);
+    if (P(0x4b,0x09) || P(0x8b,0x89) || P(0x1f,0x19) || P(0x3b,0x19))
+        return interp_2px(w4, 3, w1, 1, 2);
+    if (P(0x7e,0x2a) || P(0xef,0xab) || P(0xbf,0x8f) || P(0x7e,0x0e))
+        return interp_3px(w4, 2, w3, 3, w1, 3, 3);
+    if (P(0xfb,0x6a) || P(0x6f,0x6e) || P(0x3f,0x3e) || P(0xfb,0xfa) ||
+        P(0xdf,0xde) || P(0xdf,0x1e))
+        return interp_2px(w4, 3, w0, 1, 2);
+    if (P(0x0a,0x00) || P(0x4f,0x4b) || P(0x9f,0x1b) || P(0x2f,0x0b) ||
+        P(0xbe,0x0a) || P(0xee,0x0a) || P(0x7e,0x0a) || P(0xeb,0x4b) ||
+        P(0x3b,0x1b))
+        return interp_3px(w4, 2, w3, 1, w1, 1, 2);
+    return interp_3px(w4, 6, w3, 1, w1, 1, 3);
+}
+
+/* Assuming p0..p8 is mapped to pixels 0..8, this function interpolates the
+ * top-left and top-center pixel in the total of the 3x3 pixels to
+ * interpolates. The function is also used for the 3 other couples of pixels
+ * defining the outline. The center pixel is not defined through this function,
+ * since it's just the same as the original value. */
+static av_always_inline void hq3x_interp_2x1(uint32_t *dst, int dst_linesize,
+                                             const uint32_t *r2y, int k,
+                                             const uint32_t *w,
+                                             int pos00, int pos01,
+                                             int p0, int p1, int p2,
+                                             int p3, int p4, int p5,
+                                             int p6, int p7, int p8,
+                                             int rotate)
+{
+    INTERP_BOOTSTRAP(rotate);
+
+    uint32_t *dst00 = &dst[dst_linesize*(pos00>>1) + (pos00&1)];
+    uint32_t *dst01 = &dst[dst_linesize*(pos01>>1) + (pos01&1)];
+
+    if ((P(0xdb,0x49) || P(0xef,0x6d)) && WDIFF(w7, w3))
+        *dst00 = interp_2px(w4, 3, w1, 1, 2);
+    else if ((P(0xbf,0x37) || P(0xdb,0x13)) && WDIFF(w1, w5))
+        *dst00 = interp_2px(w4, 3, w3, 1, 2);
+    else if ((P(0x0b,0x0b) || P(0xfe,0x4a) || P(0xfe,0x1a)) && WDIFF(w3, w1))
+        *dst00 = w4;
+    else if ((P(0x6f,0x2a) || P(0x5b,0x0a) || P(0xbf,0x3a) || P(0xdf,0x5a) ||
+              P(0x9f,0x8a) || P(0xcf,0x8a) || P(0xef,0x4e) || P(0x3f,0x0e) ||
+              P(0xfb,0x5a) || P(0xbb,0x8a) || P(0x7f,0x5a) || P(0xaf,0x8a) ||
+              P(0xeb,0x8a)) && WDIFF(w3, w1))
+        *dst00 = interp_2px(w4, 3, w0, 1, 2);
+    else if (P(0x4b,0x09) || P(0x8b,0x89) || P(0x1f,0x19) || P(0x3b,0x19))
+        *dst00 = interp_2px(w4, 3, w1, 1, 2);
+    else if (P(0x1b,0x03) || P(0x4f,0x43) || P(0x8b,0x83) || P(0x6b,0x43))
+        *dst00 = interp_2px(w4, 3, w3, 1, 2);
+    else if (P(0x7e,0x2a) || P(0xef,0xab) || P(0xbf,0x8f) || P(0x7e,0x0e))
+        *dst00 = interp_2px(w3, 1, w1, 1, 1);
+    else if (P(0x4f,0x4b) || P(0x9f,0x1b) || P(0x2f,0x0b) || P(0xbe,0x0a) ||
+             P(0xee,0x0a) || P(0x7e,0x0a) || P(0xeb,0x4b) || P(0x3b,0x1b))
+        *dst00 = interp_3px(w4, 2, w3, 7, w1, 7, 4);
+    else if (P(0x0b,0x08) || P(0xf9,0x68) || P(0xf3,0x62) || P(0x6d,0x6c) ||
+             P(0x67,0x66) || P(0x3d,0x3c) || P(0x37,0x36) || P(0xf9,0xf8) ||
+             P(0xdd,0xdc) || P(0xf3,0xf2) || P(0xd7,0xd6) || P(0xdd,0x1c) ||
+             P(0xd7,0x16) || P(0x0b,0x02))
+        *dst00 = interp_2px(w4, 3, w0, 1, 2);
+    else
+        *dst00 = interp_3px(w4, 2, w3, 1, w1, 1, 2);
+
+    if ((P(0xfe,0xde) || P(0x9e,0x16) || P(0xda,0x12) || P(0x17,0x16) ||
+         P(0x5b,0x12) || P(0xbb,0x12)) && WDIFF(w1, w5))
+        *dst01 = w4;
+    else if ((P(0x0f,0x0b) || P(0x5e,0x0a) || P(0xfb,0x7b) || P(0x3b,0x0b) ||
+              P(0xbe,0x0a) || P(0x7a,0x0a)) && WDIFF(w3, w1))
+        *dst01 = w4;
+    else if (P(0xbf,0x8f) || P(0x7e,0x0e) || P(0xbf,0x37) || P(0xdb,0x13))
+        *dst01 = interp_2px(w1, 3, w4, 1, 2);
+    else if (P(0x02,0x00) || P(0x7c,0x28) || P(0xed,0xa9) || P(0xf5,0xb4) ||
+             P(0xd9,0x90))
+        *dst01 = interp_2px(w4, 3, w1, 1, 2);
+    else if (P(0x4f,0x4b) || P(0xfb,0x7b) || P(0xfe,0x7e) || P(0x9f,0x1b) ||
+             P(0x2f,0x0b) || P(0xbe,0x0a) || P(0x7e,0x0a) || P(0xfb,0x4b) ||
+             P(0xfb,0xdb) || P(0xfe,0xde) || P(0xfe,0x56) || P(0x57,0x56) ||
+             P(0x97,0x16) || P(0x3f,0x1e) || P(0xdb,0x12) || P(0xbb,0x12))
+        *dst01 = interp_2px(w4, 7, w1, 1, 3);
+    else
+        *dst01 = w4;
+}
+
+/* Assuming p0..p8 is mapped to pixels 0..8, this function interpolates the
+ * top-left block of 2x2 pixels in the total of the 4x4 pixels (or 4 blocks) to
+ * interpolates. The function is also used for the 3 other blocks of 2x2
+ * pixels. */
+static av_always_inline void hq4x_interp_2x2(uint32_t *dst, int dst_linesize,
+                                             const uint32_t *r2y, int k,
+                                             const uint32_t *w,
+                                             int pos00, int pos01,
+                                             int pos10, int pos11,
+                                             int p0, int p1, int p2,
+                                             int p3, int p4, int p5,
+                                             int p6, int p7, int p8)
+{
+    INTERP_BOOTSTRAP(0);
+
+    uint32_t *dst00 = &dst[dst_linesize*(pos00>>1) + (pos00&1)];
+    uint32_t *dst01 = &dst[dst_linesize*(pos01>>1) + (pos01&1)];
+    uint32_t *dst10 = &dst[dst_linesize*(pos10>>1) + (pos10&1)];
+    uint32_t *dst11 = &dst[dst_linesize*(pos11>>1) + (pos11&1)];
+
+    const int cond00 = (P(0xbf,0x37) || P(0xdb,0x13)) && WDIFF(w1, w5);
+    const int cond01 = (P(0xdb,0x49) || P(0xef,0x6d)) && WDIFF(w7, w3);
+    const int cond02 = (P(0x6f,0x2a) || P(0x5b,0x0a) || P(0xbf,0x3a) ||
+                        P(0xdf,0x5a) || P(0x9f,0x8a) || P(0xcf,0x8a) ||
+                        P(0xef,0x4e) || P(0x3f,0x0e) || P(0xfb,0x5a) ||
+                        P(0xbb,0x8a) || P(0x7f,0x5a) || P(0xaf,0x8a) ||
+                        P(0xeb,0x8a)) && WDIFF(w3, w1);
+    const int cond03 = P(0xdb,0x49) || P(0xef,0x6d);
+    const int cond04 = P(0xbf,0x37) || P(0xdb,0x13);
+    const int cond05 = P(0x1b,0x03) || P(0x4f,0x43) || P(0x8b,0x83) ||
+                       P(0x6b,0x43);
+    const int cond06 = P(0x4b,0x09) || P(0x8b,0x89) || P(0x1f,0x19) ||
+                       P(0x3b,0x19);
+    const int cond07 = P(0x0b,0x08) || P(0xf9,0x68) || P(0xf3,0x62) ||
+                       P(0x6d,0x6c) || P(0x67,0x66) || P(0x3d,0x3c) ||
+                       P(0x37,0x36) || P(0xf9,0xf8) || P(0xdd,0xdc) ||
+                       P(0xf3,0xf2) || P(0xd7,0xd6) || P(0xdd,0x1c) ||
+                       P(0xd7,0x16) || P(0x0b,0x02);
+    const int cond08 = (P(0x0f,0x0b) || P(0x2b,0x0b) || P(0xfe,0x4a) ||
+                        P(0xfe,0x1a)) && WDIFF(w3, w1);
+    const int cond09 = P(0x2f,0x2f);
+    const int cond10 = P(0x0a,0x00);
+    const int cond11 = P(0x0b,0x09);
+    const int cond12 = P(0x7e,0x2a) || P(0xef,0xab);
+    const int cond13 = P(0xbf,0x8f) || P(0x7e,0x0e);
+    const int cond14 = P(0x4f,0x4b) || P(0x9f,0x1b) || P(0x2f,0x0b) ||
+                       P(0xbe,0x0a) || P(0xee,0x0a) || P(0x7e,0x0a) ||
+                       P(0xeb,0x4b) || P(0x3b,0x1b);
+    const int cond15 = P(0x0b,0x03);
+
+    if (cond00)
+        *dst00 = interp_2px(w4, 5, w3, 3, 3);
+    else if (cond01)
+        *dst00 = interp_2px(w4, 5, w1, 3, 3);
+    else if ((P(0x0b,0x0b) || P(0xfe,0x4a) || P(0xfe,0x1a)) && WDIFF(w3, w1))
+        *dst00 = w4;
+    else if (cond02)
+        *dst00 = interp_2px(w4, 5, w0, 3, 3);
+    else if (cond03)
+        *dst00 = interp_2px(w4, 3, w3, 1, 2);
+    else if (cond04)
+        *dst00 = interp_2px(w4, 3, w1, 1, 2);
+    else if (cond05)
+        *dst00 = interp_2px(w4, 5, w3, 3, 3);
+    else if (cond06)
+        *dst00 = interp_2px(w4, 5, w1, 3, 3);
+    else if (P(0x0f,0x0b) || P(0x5e,0x0a) || P(0x2b,0x0b) || P(0xbe,0x0a) ||
+             P(0x7a,0x0a) || P(0xee,0x0a))
+        *dst00 = interp_2px(w1, 1, w3, 1, 1);
+    else if (cond07)
+        *dst00 = interp_2px(w4, 5, w0, 3, 3);
+    else
+        *dst00 = interp_3px(w4, 2, w1, 1, w3, 1, 2);
+
+    if (cond00)
+        *dst01 = interp_2px(w4, 7, w3, 1, 3);
+    else if (cond08)
+        *dst01 = w4;
+    else if (cond02)
+        *dst01 = interp_2px(w4, 3, w0, 1, 2);
+    else if (cond09)
+        *dst01 = w4;
+    else if (cond10)
+        *dst01 = interp_3px(w4, 5, w1, 2, w3, 1, 3);
+    else if (P(0x0b,0x08))
+        *dst01 = interp_3px(w4, 5, w1, 2, w0, 1, 3);
+    else if (cond11)
+        *dst01 = interp_2px(w4, 5, w1, 3, 3);
+    else if (cond04)
+        *dst01 = interp_2px(w1, 3, w4, 1, 2);
+    else if (cond12)
+        *dst01 = interp_3px(w1, 2, w4, 1, w3, 1, 2);
+    else if (cond13)
+        *dst01 = interp_2px(w1, 5, w3, 3, 3);
+    else if (cond05)
+        *dst01 = interp_2px(w4, 7, w3, 1, 3);
+    else if (P(0xf3,0x62) || P(0x67,0x66) || P(0x37,0x36) || P(0xf3,0xf2) ||
+             P(0xd7,0xd6) || P(0xd7,0x16) || P(0x0b,0x02))
+        *dst01 = interp_2px(w4, 3, w0, 1, 2);
+    else if (cond14)
+        *dst01 = interp_2px(w1, 1, w4, 1, 1);
+    else
+        *dst01 = interp_2px(w4, 3, w1, 1, 2);
+
+    if (cond01)
+        *dst10 = interp_2px(w4, 7, w1, 1, 3);
+    else if (cond08)
+        *dst10 = w4;
+    else if (cond02)
+        *dst10 = interp_2px(w4, 3, w0, 1, 2);
+    else if (cond09)
+        *dst10 = w4;
+    else if (cond10)
+        *dst10 = interp_3px(w4, 5, w3, 2, w1, 1, 3);
+    else if (P(0x0b,0x02))
+        *dst10 = interp_3px(w4, 5, w3, 2, w0, 1, 3);
+    else if (cond15)
+        *dst10 = interp_2px(w4, 5, w3, 3, 3);
+    else if (cond03)
+        *dst10 = interp_2px(w3, 3, w4, 1, 2);
+    else if (cond13)
+        *dst10 = interp_3px(w3, 2, w4, 1, w1, 1, 2);
+    else if (cond12)
+        *dst10 = interp_2px(w3, 5, w1, 3, 3);
+    else if (cond06)
+        *dst10 = interp_2px(w4, 7, w1, 1, 3);
+    else if (P(0x0b,0x08) || P(0xf9,0x68) || P(0x6d,0x6c) || P(0x3d,0x3c) ||
+             P(0xf9,0xf8) || P(0xdd,0xdc) || P(0xdd,0x1c))
+        *dst10 = interp_2px(w4, 3, w0, 1, 2);
+    else if (cond14)
+        *dst10 = interp_2px(w3, 1, w4, 1, 1);
+    else
+        *dst10 = interp_2px(w4, 3, w3, 1, 2);
+
+    if ((P(0x7f,0x2b) || P(0xef,0xab) || P(0xbf,0x8f) || P(0x7f,0x0f)) &&
+         WDIFF(w3, w1))
+        *dst11 = w4;
+    else if (cond02)
+        *dst11 = interp_2px(w4, 7, w0, 1, 3);
+    else if (cond15)
+        *dst11 = interp_2px(w4, 7, w3, 1, 3);
+    else if (cond11)
+        *dst11 = interp_2px(w4, 7, w1, 1, 3);
+    else if (P(0x0a,0x00) || P(0x7e,0x2a) || P(0xef,0xab) || P(0xbf,0x8f) ||
+             P(0x7e,0x0e))
+        *dst11 = interp_3px(w4, 6, w3, 1, w1, 1, 3);
+    else if (cond07)
+        *dst11 = interp_2px(w4, 7, w0, 1, 3);
+    else
+        *dst11 = w4;
+}
+
+static av_always_inline void hqx_filter(const ThreadData *td, int jobnr, int nb_jobs, int n)
+{
+    int x, y;
+    AVFrame *in = td->in, *out = td->out;
+    const uint32_t *r2y = td->rgbtoyuv;
+    const int height = in->height;
+    const int width  = in->width;
+    const int slice_start = (height *  jobnr   ) / nb_jobs;
+    const int slice_end   = (height * (jobnr+1)) / nb_jobs;
+    const int dst_linesize = out->linesize[0];
+    const int src_linesize =  in->linesize[0];
+    uint8_t       *dst = out->data[0] + slice_start * dst_linesize * n;
+    const uint8_t *src =  in->data[0] + slice_start * src_linesize;
+
+    const int dst32_linesize = dst_linesize >> 2;
+    const int src32_linesize = src_linesize >> 2;
+
+    for (y = slice_start; y < slice_end; y++) {
+        const uint32_t *src32 = (const uint32_t *)src;
+        uint32_t       *dst32 = (uint32_t *)dst;
+        const int prevline = y > 0          ? -src32_linesize : 0;
+        const int nextline = y < height - 1 ?  src32_linesize : 0;
+
+        for (x = 0; x < width; x++) {
+            uint32_t yuv1, yuv2;
+            const int prevcol = x > 0        ? -1 : 0;
+            const int nextcol = x < width -1 ?  1 : 0;
+            int pattern = 0, flag = 1, k;
+            const uint32_t w[3*3] = {
+                src32[prevcol + prevline], src32[prevline], src32[prevline + nextcol],
+                src32[prevcol           ], src32[       0], src32[           nextcol],
+                src32[prevcol + nextline], src32[nextline], src32[nextline + nextcol]
+            };
+
+            yuv1 = rgb2yuv(r2y, w[4]);
+
+            for (k = 0; k < FF_ARRAY_ELEMS(w); k++) {
+                if (k == 4)
+                    continue;
+                if (w[k] != w[4]) {
+                    yuv2 = rgb2yuv(r2y, w[k]);
+                    if (yuv_diff(yuv1, yuv2))
+                        pattern |= flag;
+                }
+                flag <<= 1;
+            }
+
+            if (n == 2) {
+                dst32[dst32_linesize*0 + 0] = hq2x_interp_1x1(r2y, pattern, w, 0,1,2,3,4,5,6,7,8);  // 00
+                dst32[dst32_linesize*0 + 1] = hq2x_interp_1x1(r2y, pattern, w, 2,1,0,5,4,3,8,7,6);  // 01 (vert mirrored)
+                dst32[dst32_linesize*1 + 0] = hq2x_interp_1x1(r2y, pattern, w, 6,7,8,3,4,5,0,1,2);  // 10 (horiz mirrored)
+                dst32[dst32_linesize*1 + 1] = hq2x_interp_1x1(r2y, pattern, w, 8,7,6,5,4,3,2,1,0);  // 11 (center mirrored)
+            } else if (n == 3) {
+                hq3x_interp_2x1(dst32,                        dst32_linesize, r2y, pattern, w, 0,1, 0,1,2,3,4,5,6,7,8, 0);  // 00 01
+                hq3x_interp_2x1(dst32 + 1,                    dst32_linesize, r2y, pattern, w, 1,3, 2,5,8,1,4,7,0,3,6, 1);  // 02 12 (rotated to the right)
+                hq3x_interp_2x1(dst32 + 1*dst32_linesize,     dst32_linesize, r2y, pattern, w, 2,0, 6,3,0,7,4,1,8,5,2, 1);  // 20 10 (rotated to the left)
+                hq3x_interp_2x1(dst32 + 1*dst32_linesize + 1, dst32_linesize, r2y, pattern, w, 3,2, 8,7,6,5,4,3,2,1,0, 0);  // 22 21 (center mirrored)
+                dst32[dst32_linesize + 1] = w[4];                                                                           // 11
+            } else if (n == 4) {
+                hq4x_interp_2x2(dst32,                        dst32_linesize, r2y, pattern, w, 0,1,2,3, 0,1,2,3,4,5,6,7,8); // 00 01 10 11
+                hq4x_interp_2x2(dst32 + 2,                    dst32_linesize, r2y, pattern, w, 1,0,3,2, 2,1,0,5,4,3,8,7,6); // 02 03 12 13 (vert mirrored)
+                hq4x_interp_2x2(dst32 + 2*dst32_linesize,     dst32_linesize, r2y, pattern, w, 2,3,0,1, 6,7,8,3,4,5,0,1,2); // 20 21 30 31 (horiz mirrored)
+                hq4x_interp_2x2(dst32 + 2*dst32_linesize + 2, dst32_linesize, r2y, pattern, w, 3,2,1,0, 8,7,6,5,4,3,2,1,0); // 22 23 32 33 (center mirrored)
+            } else {
+                av_assert0(0);
+            }
+
+            src32 += 1;
+            dst32 += n;
+        }
+
+        src += src_linesize;
+        dst += dst_linesize * n;
+    }
+}
+
+#define HQX_FUNC(size) \
+static int hq##size##x(AVFilterContext *ctx, void *arg, int jobnr, int nb_jobs) \
+{ \
+    hqx_filter(arg, jobnr, nb_jobs, size); \
+    return 0; \
+}
+
+HQX_FUNC(2)
+HQX_FUNC(3)
+HQX_FUNC(4)
+
+static int query_formats(AVFilterContext *ctx)
+{
+    static const enum AVPixelFormat pix_fmts[] = {AV_PIX_FMT_BGRA, AV_PIX_FMT_NONE};
+    ff_set_common_formats(ctx, ff_make_format_list(pix_fmts));
+    return 0;
+}
+
+static int config_output(AVFilterLink *outlink)
+{
+    AVFilterContext *ctx = outlink->src;
+    HQXContext *hqx = ctx->priv;
+    AVFilterLink *inlink = ctx->inputs[0];
+
+    outlink->w = inlink->w * hqx->n;
+    outlink->h = inlink->h * hqx->n;
+    av_log(inlink->dst, AV_LOG_VERBOSE, "fmt:%s size:%dx%d -> size:%dx%d\n",
+           av_get_pix_fmt_name(inlink->format),
+           inlink->w, inlink->h, outlink->w, outlink->h);
+    return 0;
+}
+
+static int filter_frame(AVFilterLink *inlink, AVFrame *in)
+{
+    AVFilterContext *ctx = inlink->dst;
+    AVFilterLink *outlink = ctx->outputs[0];
+    HQXContext *hqx = ctx->priv;
+    ThreadData td;
+    AVFrame *out = ff_get_video_buffer(outlink, outlink->w, outlink->h);
+    if (!out) {
+        av_frame_free(&in);
+        return AVERROR(ENOMEM);
+    }
+    av_frame_copy_props(out, in);
+    out->width  = outlink->w;
+    out->height = outlink->h;
+
+    td.in = in;
+    td.out = out;
+    td.rgbtoyuv = hqx->rgbtoyuv;
+    ctx->internal->execute(ctx, hqx->func, &td, NULL, FFMIN(inlink->h, ctx->graph->nb_threads));
+
+    av_frame_free(&in);
+    return ff_filter_frame(outlink, out);
+}
+
+static av_cold int init(AVFilterContext *ctx)
+{
+    HQXContext *hqx = ctx->priv;
+    static const hqxfunc_t hqxfuncs[] = {hq2x, hq3x, hq4x};
+
+    uint32_t c;
+    for (c = 0; c < FF_ARRAY_ELEMS(hqx->rgbtoyuv); c++) {
+        const uint32_t r = c >> 16 & 0xff;
+        const uint32_t g = c >>  8 & 0xff;
+        const uint32_t b = c       & 0xff;
+        const uint32_t y = (uint32_t)( 0.299*r + 0.587*g + 0.114*b);
+        const uint32_t u = (uint32_t)(-0.169*r - 0.331*g +   0.5*b) + 128;
+        const uint32_t v = (uint32_t)(   0.5*r - 0.419*g - 0.081*b) + 128;
+        hqx->rgbtoyuv[c] = (y << 16) + (u << 8) + v;
+    }
+
+    hqx->func = hqxfuncs[hqx->n - 2];
+    return 0;
+}
+
+static const AVFilterPad hqx_inputs[] = {
+    {
+        .name         = "default",
+        .type         = AVMEDIA_TYPE_VIDEO,
+        .filter_frame = filter_frame,
+    },
+    { NULL }
+};
+
+static const AVFilterPad hqx_outputs[] = {
+    {
+        .name         = "default",
+        .type         = AVMEDIA_TYPE_VIDEO,
+        .config_props = config_output,
+    },
+    { NULL }
+};
+
+AVFilter ff_vf_hqx = {
+    .name          = "hqx",
+    .description   = NULL_IF_CONFIG_SMALL("Scale the input by 2, 3 or 4 using the hq*x magnification algorithm."),
+    .priv_size     = sizeof(HQXContext),
+    .init          = init,
+    .query_formats = query_formats,
+    .inputs        = hqx_inputs,
+    .outputs       = hqx_outputs,
+    .priv_class    = &hqx_class,
+    .flags         = AVFILTER_FLAG_SLICE_THREADS,
+};
diff --git a/tests/fate/filter-video.mak b/tests/fate/filter-video.mak
index 0241f02fcd..f5f7573de4 100644
--- a/tests/fate/filter-video.mak
+++ b/tests/fate/filter-video.mak
@@ -146,6 +146,13 @@ FATE_FILTER-$(call ALLYES, SMJPEG_DEMUXER MJPEG_DECODER PERMS_FILTER HQDN3D_FILT
 fate-filter-hqdn3d-sample: tests/data/filtergraphs/hqdn3d
 fate-filter-hqdn3d-sample: CMD = framecrc -idct simple -i $(TARGET_SAMPLES)/smjpeg/scenwin.mjpg -filter_complex_script $(TARGET_PATH)/tests/data/filtergraphs/hqdn3d -an
 
+FATE_FILTER_HQX-$(call ALLYES, IMAGE2_DEMUXER PNG_DECODER HQX_FILTER) = fate-filter-hq2x fate-filter-hq3x fate-filter-hq4x
+FATE_FILTER-yes += $(FATE_FILTER_HQX-yes)
+fate-filter-hq2x: CMD = framecrc -i $(TARGET_SAMPLES)/filter/pixelart%d.png -vf hqx=2
+fate-filter-hq3x: CMD = framecrc -i $(TARGET_SAMPLES)/filter/pixelart%d.png -vf hqx=3
+fate-filter-hq4x: CMD = framecrc -i $(TARGET_SAMPLES)/filter/pixelart%d.png -vf hqx=4
+fate-filter-hqx: $(FATE_FILTER_HQX-yes)
+
 FATE_FILTER-$(call ALLYES, UTVIDEO_DECODER AVI_DEMUXER PERMS_FILTER CURVES_FILTER) += fate-filter-curves
 fate-filter-curves: CMD = framecrc -i $(TARGET_SAMPLES)/utvideo/utvideo_rgb_median.avi -vf perms=random,curves=vintage
 
diff --git a/tests/ref/fate/filter-hq2x b/tests/ref/fate/filter-hq2x
new file mode 100644
index 0000000000..dcf2a291cd
--- /dev/null
+++ b/tests/ref/fate/filter-hq2x
@@ -0,0 +1,3 @@
+#tb 0: 1/25
+0,          0,          0,        1,   877072, 0x9369339e
+0,          1,          1,        1,   877072, 0x32d119a1
diff --git a/tests/ref/fate/filter-hq3x b/tests/ref/fate/filter-hq3x
new file mode 100644
index 0000000000..82153881d4
--- /dev/null
+++ b/tests/ref/fate/filter-hq3x
@@ -0,0 +1,3 @@
+#tb 0: 1/25
+0,          0,          0,        1,  1973412, 0xafc227fa
+0,          1,          1,        1,  1973412, 0x93aebf19
diff --git a/tests/ref/fate/filter-hq4x b/tests/ref/fate/filter-hq4x
new file mode 100644
index 0000000000..c1d6fd8fac
--- /dev/null
+++ b/tests/ref/fate/filter-hq4x
@@ -0,0 +1,3 @@
+#tb 0: 1/25
+0,          0,          0,        1,  3508288, 0x034ef75e
+0,          1,          1,        1,  3508288, 0x738e9bbb