[PATCH] avfilter: add inverse tone mapping
Sarthak Indurkhya
sindurkhya at adobe.com
Sat Jul 5 21:20:50 EEST 2025
Hello FFmpeg developers,
This patch introduces a new video filter called inversetonemap for FFmpeg.
The filter performs SDR to HDR conversion by mapping SDR BT.709 video to HDR BT.2020 PQ, using local adaptation and inverse tone mapping. The goal is to provide a simple, flexible tool for upconverting SDR content for HDR displays, with local adaptation, tone curve sensitivity, and chroma processing.
Please review.
Thanks,
Sarthak
--
>From f563ee1ad93511dfe7dd252578d7801e0cbbe968 Mon Sep 17 00:00:00 2001
From: Sarthak Indurkhya sarthak at Sarthaks-MacBook-Pro.local<mailto:sarthak at Sarthaks-MacBook-Pro.local>
Date: Sat, 5 Jul 2025 22:33:46 +0530
Subject: [PATCH] avfilter: add inversetonemap filter
This filter performs inverse tone mapping from SDR to HDR using local adaptation and PQ mapping.
- Added inversetonemap video filter for SDR to HDR conversion.
---
Changelog | 1 +
libavfilter/Makefile | 1 +
libavfilter/allfilters.c | 1 +
libavfilter/vf_inversetonemap.c | 98 ++++++++++++++++-----------------
4 files changed, 51 insertions(+), 50 deletions(-)
diff --git a/Changelog b/Changelog
index 81e2cc813f..0aecf6dbf1 100644
--- a/Changelog
+++ b/Changelog
@@ -2,6 +2,7 @@ Entries are sorted chronologically from oldest to youngest within each release,
releases are sorted from youngest to oldest.
version <next>:
+- Added inversetonemap video filter for SDR to HDR conversion.
- yasm support dropped, users need to use nasm
- VVC VAAPI decoder
- RealVideo 6.0 decoder
diff --git a/libavfilter/Makefile b/libavfilter/Makefile
index 97f8f17272..e715a3a5e4 100644
--- a/libavfilter/Makefile
+++ b/libavfilter/Makefile
@@ -191,6 +191,7 @@ OBJS-$(CONFIG_SINE_FILTER) += asrc_sine.o
OBJS-$(CONFIG_ANULLSINK_FILTER) += asink_anullsink.o
# video filters
+OBJS-$(CONFIG_INVERSETONEMAP_FILTER) += vf_inversetonemap.o
OBJS-$(CONFIG_ADDROI_FILTER) += vf_addroi.o
OBJS-$(CONFIG_ALPHAEXTRACT_FILTER) += vf_extractplanes.o
OBJS-$(CONFIG_ALPHAMERGE_FILTER) += vf_alphamerge.o framesync.o
diff --git a/libavfilter/allfilters.c b/libavfilter/allfilters.c
index 3bc045b28f..2f67300ca1 100644
--- a/libavfilter/allfilters.c
+++ b/libavfilter/allfilters.c
@@ -176,6 +176,7 @@ extern const FFFilter ff_asrc_sine;
extern const FFFilter ff_asink_anullsink;
+extern const FFFilter ff_vf_inversetonemap;
extern const FFFilter ff_vf_addroi;
extern const FFFilter ff_vf_alphaextract;
extern const FFFilter ff_vf_alphamerge;
diff --git a/libavfilter/vf_inversetonemap.c b/libavfilter/vf_inversetonemap.c
index 28ea1ef29e..d8d8920151 100644
--- a/libavfilter/vf_inversetonemap.c
+++ b/libavfilter/vf_inversetonemap.c
@@ -1,3 +1,22 @@
+/*
+ * Copyright (c) 2025 Sarthak Indurkhya
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
/**
* @file
* @brief SDR to HDR inverse tone mapping filter for FFmpeg
@@ -38,7 +57,7 @@ typedef struct FilterContext {
float HDR_max;
} FilterContext;
-//declaring lookup table
+
static float bt709_gamma_lut[256];
static void init_bt709_gamma_lut(void) {
@@ -51,14 +70,13 @@ static void init_bt709_gamma_lut(void) {
}
}
-// Rec.709 to Rec.2020 matrix
+
static const float bt709_to_bt2020[3][3] = {
{0.6274f, 0.3293f, 0.0433f},
{0.0691f, 0.9195f, 0.0114f},
{0.0164f, 0.0880f, 0.8956f}
};
-// PQ transfer function
#define PQ_M1 0.1593017578125f
#define PQ_M2 78.84375f
#define PQ_C1 0.8359375f
@@ -80,12 +98,10 @@ static void compute_local_adaptation(const float *R_full, float *sigma, int widt
float *temp_blur = av_mallocz(npix * sizeof(float));
float *spatial_weights = av_malloc((2 * radius + 1) * sizeof(float));
- // 1D Gaussian kernel for separable blur
for (int i = -radius; i <= radius; i++) {
spatial_weights[i + radius] = expf(-(i * i) / (2 * sigma_spatial * sigma_spatial));
}
- // Scene max luminance
float scene_max = 1e-6f;
for (int i = 0; i < npix; i++) {
if (R_full[i] > scene_max)
@@ -93,7 +109,6 @@ static void compute_local_adaptation(const float *R_full, float *sigma, int widt
}
float hdr_scale = HDR_max / scene_max;
- // ---- Horizontal blur pass ----
for (int y = 0; y < height; y++) {
for (int x = 0; x < width; x++) {
float sum = 0.0f, sum_weights = 0.0f;
@@ -113,7 +128,6 @@ static void compute_local_adaptation(const float *R_full, float *sigma, int widt
}
}
- // ---- Vertical blur pass ----
for (int y = 0; y < height; y++) {
for (int x = 0; x < width; x++) {
float sum = 0.0f, sum_weights = 0.0f;
@@ -137,18 +151,15 @@ static void compute_local_adaptation(const float *R_full, float *sigma, int widt
av_free(spatial_weights);
}
static void compute_local_adaptation_fast(const float *R_full, float *sigma, int width, int height,
- float sigma_spatial, float sigma_range, float HDR_max)
-{
+ float sigma_spatial, float sigma_range, float HDR_max){
const int scale = 4;
int down_w = width / scale;
int down_h = height / scale;
int npix_small = down_w * down_h;
- // Allocating downsampled and result buffers
float *R_small = av_malloc(npix_small * sizeof(float));
float *sigma_small = av_malloc(npix_small * sizeof(float));
- // Simple box downsampling
for (int y = 0; y < down_h; y++) {
for (int x = 0; x < down_w; x++) {
float sum = 0.0f;
@@ -167,7 +178,6 @@ static void compute_local_adaptation_fast(const float *R_full, float *sigma, int
compute_local_adaptation(R_small, sigma_small, down_w, down_h, sigma_spatial, sigma_range, HDR_max);
- // Upsampling sigma_small -> sigma
struct SwsContext *sws_ctx = sws_getContext(down_w, down_h, AV_PIX_FMT_GRAYF32,
width, height, AV_PIX_FMT_GRAYF32,
SWS_BILINEAR, NULL, NULL, NULL);
@@ -199,14 +209,12 @@ static void compute_hdr_intensity(const float *R_full, const float *sigma, float
static void inverse_tone_map_linear_rgb(
const float *R, const float *G, const float *B,
float *R_hdr, float *G_hdr, float *B_hdr,
- int width, int height, FilterContext *s)
-{
+ int width, int height, FilterContext *s){
int npix = width * height;
float *Y = av_malloc(npix * sizeof(float));
float *Y_sigma = av_malloc(npix * sizeof(float));
float *Y_hdr = av_malloc(npix * sizeof(float));
- // Computing luminance (BT.2020)
for (int i = 0; i < npix; i++)
Y[i] = 0.2627f * R[i] + 0.6780f * G[i] + 0.0593f * B[i];
@@ -215,7 +223,6 @@ static void inverse_tone_map_linear_rgb(
compute_hdr_intensity(Y, Y_sigma, Y_hdr, width, height, s->n, 1.0f);
- // Scaling RGB channels
for (int i = 0; i < npix; i++) {
float scale = Y_hdr[i] / (Y[i] + 1e-6f);
R_hdr[i] = R[i] * scale;
@@ -249,11 +256,20 @@ static void dither_pq_to_10bit(const float *pq, uint16_t *y_temp, int width, int
}
static int fil_func(AVFilterLink *inlink, AVFrame *in) {
+ const float exposure = 3.5f;
+ const float contrast = 1.02f;
+ const float black = 0.03f;
+ const float white = 8.0f;
+ const float s_curve_pow = 1.00f;
+ const float white_balance_r = 1.0f;
+ const float white_balance_g = 1.0f;
+ const float white_balance_b = 1.1f;
+
AVFilterContext *ctx = inlink->dst;
FilterContext *s = ctx->priv;
int width = in->width, height = in->height, npix = width * height;
- // Converting to RGB24
+
struct SwsContext *sws_ctx = sws_getContext(
width, height, in->format,
width, height, AV_PIX_FMT_RGB24,
@@ -272,9 +288,6 @@ static int fil_func(AVFilterLink *inlink, AVFrame *in) {
rgb_frame->data, rgb_frame->linesize);
sws_freeContext(sws_ctx);
- //Calling gamma lookup table initialization
- init_bt709_gamma_lut();
- // Gamma linearization & gamut mapping
float *R = av_malloc(npix * sizeof(float));
float *G = av_malloc(npix * sizeof(float));
float *B = av_malloc(npix * sizeof(float));
@@ -290,20 +303,21 @@ static int fil_func(AVFilterLink *inlink, AVFrame *in) {
}
}
- // Inverse Tone Mapping
float *R_hdr = av_malloc(npix * sizeof(float));
float *G_hdr = av_malloc(npix * sizeof(float));
float *B_hdr = av_malloc(npix * sizeof(float));
inverse_tone_map_linear_rgb(R, G, B, R_hdr, G_hdr, B_hdr, width, height, s);
- float exposure = 3.5f; //4.0
- float contrast = 1.02f; //1.10
- float black = 0.03f, white = 8.0f; //0.04 //12.0
- float s_curve_pow = 1.00f; //0.70
+ /*
+ float exposure = 3.5f; //4.0
+ float contrast = 1.02f; //1.10
+ float black = 0.03f, white = 8.0f; //0.04 //12.0
+ float s_curve_pow = 1.00f; //0.70
+ */
for (int i = 0; i < npix; i++) {
- float r = R[i] * exposure, g = G[i] * exposure, b = B[i] * exposure;
+ float r = R_hdr[i] * exposure, g = G_hdr[i] * exposure, b = B_hdr[i] * exposure;
float lum = 0.2627f * r + 0.6780f * g + 0.0593f * b;
@@ -316,21 +330,14 @@ static int fil_func(AVFilterLink *inlink, AVFrame *in) {
g *= scale;
b *= scale;
- // Contrast
r = (r - 0.5f) * contrast + 0.5f;
g = (g - 0.5f) * contrast + 0.5f;
b = (b - 0.5f) * contrast + 0.5f;
- // White balance correction
- float white_balance_r = 1.0f;
- float white_balance_g = 1.0f;
- float white_balance_b = 1.1f;
-
r *= white_balance_r;
g *= white_balance_g;
b *= white_balance_b;
- // Final clamp
r = fminf(fmaxf(r, 0.0f), 1.0f);
g = fminf(fmaxf(g, 0.0f), 1.0f);
b = fminf(fmaxf(b, 0.0f), 1.0f);
@@ -340,18 +347,16 @@ static int fil_func(AVFilterLink *inlink, AVFrame *in) {
B_hdr[i] = b;
}
- //Computing linear luminance (BT.2020)
float *Y = av_malloc(npix * sizeof(float));
for (int i = 0; i < npix; i++)
Y[i] = 0.2627f * R_hdr[i] + 0.6780f * G_hdr[i] + 0.0593f * B_hdr[i];
- // Applying PQ transfer
float *pq = av_malloc(npix * sizeof(float));
for (int i = 0; i < npix; i++) {
pq[i] = linear_to_pq(Y[i] * (10000.0f / s->HDR_max));
pq[i] = fminf(fmaxf(pq[i], 0.0f), 1.0f);
}
- //Allocating output frame (YUV420P10LE)
+
AVFrame *out = av_frame_alloc();
out->format = AV_PIX_FMT_YUV420P10LE;
out->width = width;
@@ -359,25 +364,21 @@ static int fil_func(AVFilterLink *inlink, AVFrame *in) {
av_frame_get_buffer(out, 32);
av_frame_copy_props(out, in);
- // Setting HDR metadata
+
out->color_primaries = AVCOL_PRI_BT2020;
- out->color_trc = AVCOL_TRC_SMPTE2084; // PQ
+ out->color_trc = AVCOL_TRC_SMPTE2084;
out->colorspace = AVCOL_SPC_BT2020_NCL;
- out->color_range = AVCOL_RANGE_MPEG; // Full range for HDR
+ out->color_range = AVCOL_RANGE_MPEG;
- // Setting mastering display metadata if available
if (out->metadata) {
- // Mastering display primaries (BT.2020)
av_dict_set(&out->metadata, "mastering_display_primaries",
"0.708,0.292,0.170,0.797,0.131,0.046,0.3127,0.3290", 0);
- // Mastering display luminance (in nits)
char luminance_str[64];
snprintf(luminance_str, sizeof(luminance_str), "%.1f,%.1f",
- s->HDR_max, 0.001f); // Max luminance, min luminance
+ s->HDR_max, 0.001f);
av_dict_set(&out->metadata, "mastering_display_luminance", luminance_str, 0);
- // Content light level
char content_light_str[64];
float max_content_light = 0.0f;
for (int i = 0; i < npix; i++) {
@@ -389,12 +390,10 @@ static int fil_func(AVFilterLink *inlink, AVFrame *in) {
av_dict_set(&out->metadata, "content_light_level", content_light_str, 0);
}
- // Clearing Y, U, V planes
av_frame_make_writable(out);
for (int y = 0; y < height; y++)
memset(out->data[0] + y * out->linesize[0], 0, out->linesize[0]);
- // Dithering PQ to 10-bit Y plane
uint16_t *y_temp = av_malloc(npix * sizeof(uint16_t));
dither_pq_to_10bit(pq, y_temp, width, height);
for (int y = 0; y < height; y++) {
@@ -402,7 +401,6 @@ static int fil_func(AVFilterLink *inlink, AVFrame *in) {
memcpy(row, y_temp + y * width, width * sizeof(uint16_t));
}
- // Computing and encoding U, V chroma planes from original SDR RGB
for (int y = 0; y < height / 2; y++) {
uint16_t *u_row = (uint16_t *)(out->data[1] + y * out->linesize[1]);
uint16_t *v_row = (uint16_t *)(out->data[2] + y * out->linesize[2]);
@@ -425,8 +423,8 @@ static int fil_func(AVFilterLink *inlink, AVFrame *in) {
float U = (b - Y_sdr) / 1.8814f;
float V = (r - Y_sdr) / 1.4746f;
float chroma_blend = 1.0f - fminf(Y_sdr, 1.0f);
- float chroma_boost = 0.85f * chroma_blend + 0.85f * (1.0f - chroma_blend); //0.8
- // float chroma_boost = 1.08f;
+ float chroma_boost = 0.85f * chroma_blend + 0.85f * (1.0f - chroma_blend);
+
U *= chroma_boost;
V *= chroma_boost;
U = fmaxf(fminf(U, 0.45f), -0.45f);
@@ -471,7 +469,7 @@ static const AVFilterPad fil_outputs[] = {
};
static int ff_filter_init(AVFilterContext *avctx) {
- av_log_set_level(AV_LOG_DEBUG);
+ init_bt709_gamma_lut();
av_log(avctx, AV_LOG_INFO, "Initializing filter with 1 input and 1 output\n");
return 0;
}
--
2.49.0
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