/*
* Copyright (c) 2017 Richard Ling
*
* 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
*/
/*
* Normalize RGB video (aka histogram stretching, contrast stretching).
* See: https://en.wikipedia.org/wiki/Normalization_(image_processing)
*
* For each channel of each frame, the filter computes the input range and maps
* it linearly to the user-specified output range. The output range defaults
* to the full dynamic range from pure black to pure white.
*
* Naively maximising the dynamic range of each frame of video in isolation
* may cause flickering (rapid changes in brightness of static objects in the
* scene) when small dark or bright objects enter or leave the scene. This
* filter can apply temporal smoothing to the input range to reduce flickering.
* Temporal smoothing is similar to the auto-exposure (automatic gain control)
* on a video camera, which performs the same function; and, like a video
* camera, it may cause a period of over- or under-exposure of the video.
*
* The filter can normalize the R,G,B channels independently, which may cause
* color shifting, or link them together as a single channel, which prevents
* color shifting. More precisely, linked normalization preserves hue (as it's
* defined in HSV/HSL color spaces) while independent normalization does not.
* Independent normalization can be used to remove color casts, such as the
* blue cast from underwater video, restoring more natural colors. The filter
* can also combine independent and linked normalization in any ratio.
*
* Finally the overall strength of the filter can be adjusted, from no effect
* to full normalization.
*
* The 5 AVOptions are:
* blackpt, Colors which define the output range. The minimum input value
* whitept is mapped to the blackpt. The maximum input value is mapped to
* the whitept. The defaults are black and white respectively.
* Specifying white for blackpt and black for whitept will give
* color-inverted, normalized video. Shades of grey can be used
* to reduce the dynamic range (contrast). Specifying saturated
* colors here can create some interesting effects.
*
* smoothing The amount of temporal smoothing, expressed in frames (>=0).
* the minimum and maximum input values of each channel are
* smoothed using a rolling average over the current frame and
* that many previous frames of video. Defaults to 0 (no temporal
* smoothing).
*
* independence
* Controls the ratio of independent (color shifting) channel
* normalization to linked (color preserving) normalization. 0.0
* is fully linked, 1.0 is fully independent. Defaults to fully
* independent.
*
* strength Overall strength of the filter. 1.0 is full strength. 0.0 is
* a rather expensive no-op. Values in between can give a gentle
* boost to low-contrast video without creating an artificial
* over-processed look. The default is full strength.
*/
#include "libavutil/imgutils.h"
#include "libavutil/opt.h"
#include "libavutil/pixdesc.h"
#include "avfilter.h"
#include "formats.h"
#include "internal.h"
#include "video.h"
typedef struct NormalizeContext {
const AVClass *class;
// Storage for the corresponding AVOptions
uint8_t blackpt[4];
uint8_t whitept[4];
int smoothing;
float independence;
float strength;
int co[4]; // Offsets to R,G,B,A bytes respectively in each pixel
int num_components; // Number of components in the pixel format
int history_len; // Number of frames to average; based on smoothing factor
int frame_num; // Increments on each frame, starting from 0.
// Per-extremum, per-channel history, for temporal smoothing.
struct {
uint8_t *history; // History entries.
uint32_t history_sum; // Sum of history entries.
} min[3], max[3]; // Min and max for each channel in {R,G,B}.
uint8_t *history_mem; // Single allocation for above history entries
} NormalizeContext;
#define OFFSET(x) offsetof(NormalizeContext, x)
#define FLAGS AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_FILTERING_PARAM
static const AVOption normalize_options[] = {
{ "blackpt", "output color to which darkest input color is mapped", OFFSET(blackpt), AV_OPT_TYPE_COLOR, { .str = "black" }, CHAR_MIN, CHAR_MAX, FLAGS },
{ "whitept", "output color to which brightest input color is mapped", OFFSET(whitept), AV_OPT_TYPE_COLOR, { .str = "white" }, CHAR_MIN, CHAR_MAX, FLAGS },
{ "smoothing", "amount of temporal smoothing of the input range, to reduce flicker", OFFSET(smoothing), AV_OPT_TYPE_INT, {.i64=0}, 0, INT_MAX/8, FLAGS },
{ "independence", "proportion of independent to linked channel normalization", OFFSET(independence), AV_OPT_TYPE_FLOAT, {.dbl=1.0}, 0.0, 1.0, FLAGS },
{ "strength", "strength of filter, from no effect to full normalization", OFFSET(strength), AV_OPT_TYPE_FLOAT, {.dbl=1.0}, 0.0, 1.0, FLAGS },
{ NULL }
};
AVFILTER_DEFINE_CLASS(normalize);
// This function is the main guts of the filter. Normalizes the input frame
// into the output frame. The frames are known to have the same dimensions
// and pixel format.
static void normalize(NormalizeContext *s, AVFrame *in, AVFrame *out)
{
// Per-extremum, per-channel local variables.
struct {
uint8_t in; // Original input byte value for this frame.
float smoothed; // Smoothed input value [0,255].
float out; // Output value [0,255].
} min[3], max[3]; // Min and max for each channel in {R,G,B}.
float rgb_min_smoothed; // Min input range for linked normalization
float rgb_max_smoothed; // Max input range for linked normalization
uint8_t lut[3][256]; // Lookup table
int x, y, c;
// First, scan the input frame to find, for each channel, the minimum
// (min.in) and maximum (max.in) values present in the channel.
for (c = 0; c < 3; c++)
min[c].in = max[c].in = in->data[0][s->co[c]];
for (y = 0; y < in->height; y++) {
uint8_t *inp = in->data[0] + y * in->linesize[0];
uint8_t *outp = out->data[0] + y * out->linesize[0];
for (x = 0; x < in->width; x++) {
for (c = 0; c < 3; c++) {
min[c].in = FFMIN(min[c].in, inp[s->co[c]]);
max[c].in = FFMAX(max[c].in, inp[s->co[c]]);
}
inp += s->num_components;
outp += s->num_components;
}
}
// Next, for each channel, push min.in and max.in into their respective
// histories, to determine the min.smoothed and max.smoothed for this frame.
{
int history_idx = s->frame_num % s->history_len;
// Assume the history is not yet full; num_history_vals is the number
// of frames received so far including the current frame.
int num_history_vals = s->frame_num + 1;
if (s->frame_num >= s->history_len) {
//The history is full; drop oldest value and cap num_history_vals.
for (c = 0; c < 3; c++) {
s->min[c].history_sum -= s->min[c].history[history_idx];
s->max[c].history_sum -= s->max[c].history[history_idx];
}
num_history_vals = s->history_len;
}
// For each extremum, update history_sum and calculate smoothed value
// as the rolling average of the history entries.
for (c = 0; c < 3; c++) {
s->min[c].history_sum += (s->min[c].history[history_idx] = min[c].in);
min[c].smoothed = s->min[c].history_sum / (float)num_history_vals;
s->max[c].history_sum += (s->max[c].history[history_idx] = max[c].in);
max[c].smoothed = s->max[c].history_sum / (float)num_history_vals;
}
}
// Determine the input range for linked normalization. This is simply the
// minimum of the per-channel minimums, and the maximum of the per-channel
// maximums.
rgb_min_smoothed = FFMIN3(min[0].smoothed, min[1].smoothed, min[2].smoothed);
rgb_max_smoothed = FFMAX3(max[0].smoothed, max[1].smoothed, max[2].smoothed);
// Now, process each channel to determine the input and output range and
// build the lookup tables.
for (c = 0; c < 3; c++) {
int in_val;
// Adjust the input range for this channel [min.smoothed,max.smoothed]
// by mixing in the correct proportion of the linked normalization
// input range [rgb_min_smoothed,rgb_max_smoothed].
min[c].smoothed = (min[c].smoothed * s->independence)
+ (rgb_min_smoothed * (1.0f - s->independence));
max[c].smoothed = (max[c].smoothed * s->independence)
+ (rgb_max_smoothed * (1.0f - s->independence));
// Calculate the output range [min.out,max.out] as a ratio of the full-
// strength output range [blackpt,whitept] and the original input range
// [min.in,max.in], based on the user-specified filter strength.
min[c].out = (s->blackpt[c] * s->strength)
+ (min[c].in * (1.0f - s->strength));
max[c].out = (s->whitept[c] * s->strength)
+ (max[c].in * (1.0f - s->strength));
// Now, build a lookup table which linearly maps the adjusted input range
// [min.smoothed,max.smoothed] to the output range [min.out,max.out].
// Perform the linear interpolation for each x:
// lut[x] = (int)(float(x - min.smoothed) * scale + max.out + 0.5)
// where scale = (max.out - min.out) / (max.smoothed - min.smoothed)
if (min[c].smoothed == max[c].smoothed) {
// There is no dynamic range to expand. No mapping for this channel.
for (in_val = min[c].in; in_val <= max[c].in; in_val++)
lut[c][in_val] = min[c].out;
} else {
// We must set lookup values for all values in the original input
// range [min.in,max.in]. Since the original input range may be
// larger than [min.smoothed,max.smoothed], some output values may
// fall outside the [0,255] dynamic range. We need to clamp them.
float scale = (max[c].out - min[c].out) / (max[c].smoothed - min[c].smoothed);
for (in_val = min[c].in; in_val <= max[c].in; in_val++) {
int out_val = (in_val - min[c].smoothed) * scale + min[c].out + 0.5f;
out_val = FFMAX(out_val, 0);
out_val = FFMIN(out_val, 255);
lut[c][in_val] = out_val;
}
}
}
// Finally, process the pixels of the input frame using the lookup tables.
for (y = 0; y < in->height; y++) {
uint8_t *inp = in->data[0] + y * in->linesize[0];
uint8_t *outp = out->data[0] + y * out->linesize[0];
for (x = 0; x < in->width; x++) {
for (c = 0; c < 3; c++)
outp[s->co[c]] = lut[c][inp[s->co[c]]];
if (s->num_components == 4)
// Copy alpha as-is.
outp[s->co[3]] = inp[s->co[3]];
inp += s->num_components;
outp += s->num_components;
}
}
s->frame_num++;
}
// Now we define all the functions accessible from the ff_vf_normalize class,
// which is ffmpeg's interface to our filter. See doc/filter_design.txt and
// doc/writing_filters.txt for descriptions of what these interface functions
// are expected to do.
// Set the pixel formats that our filter supports. We should be able to process
// any 8-bit RGB formats. 16-bit support might be useful one day.
static int query_formats(AVFilterContext *ctx)
{
static const enum AVPixelFormat pixel_fmts[] = {
AV_PIX_FMT_RGB24,
AV_PIX_FMT_BGR24,
AV_PIX_FMT_ARGB,
AV_PIX_FMT_RGBA,
AV_PIX_FMT_ABGR,
AV_PIX_FMT_BGRA,
AV_PIX_FMT_0RGB,
AV_PIX_FMT_RGB0,
AV_PIX_FMT_0BGR,
AV_PIX_FMT_BGR0,
AV_PIX_FMT_NONE
};
// According to filter_design.txt, using ff_set_common_formats() this way
// ensures the pixel formats of the input and output will be the same. That
// saves a bit of effort possibly needing to handle format conversions.
AVFilterFormats *formats = ff_make_format_list(pixel_fmts);
if (!formats)
return AVERROR(ENOMEM);
return ff_set_common_formats(ctx, formats);
}
// At this point we know the pixel format used for both input and output. We
// can also access the frame rate of the input video and allocate some memory
// appropriately
static int config_input(AVFilterLink *inlink)
{
NormalizeContext *s = inlink->dst->priv;
// Store offsets to R,G,B,A bytes respectively in each pixel
const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(inlink->format);
int c;
for (c = 0; c < 4; ++c)
s->co[c] = desc->comp[c].offset;
s->num_components = desc->nb_components;
// Convert smoothing value to history_len (a count of frames to average,
// must be at least 1). Currently this is a direct assignment, but the
// smoothing value was originally envisaged as a number of seconds. In
// future it would be nice to set history_len using a number of seconds,
// but VFR video is currently an obstacle to doing so.
s->history_len = s->smoothing + 1;
// Allocate the history buffers -- there are 6 -- one for each extrema.
// s->smoothing is limited to INT_MAX/8, so that (s->history_len * 6)
// can't overflow on 32bit causing a too-small allocation.
s->history_mem = av_malloc(s->history_len * 6);
if (s->history_mem == NULL)
return AVERROR(ENOMEM);
for (c = 0; c < 3; c++) {
s->min[c].history = s->history_mem + (c*2) * s->history_len;
s->max[c].history = s->history_mem + (c*2+1) * s->history_len;
}
return 0;
}
// Free any memory allocations here
static av_cold void uninit(AVFilterContext *ctx)
{
NormalizeContext *s = ctx->priv;
av_freep(&s->history_mem);
}
// This function is pretty much standard from doc/writing_filters.txt. It
// tries to do in-place filtering where possible, only allocating a new output
// frame when absolutely necessary.
static int filter_frame(AVFilterLink *inlink, AVFrame *in)
{
AVFilterContext *ctx = inlink->dst;
AVFilterLink *outlink = ctx->outputs[0];
NormalizeContext *s = ctx->priv;
AVFrame *out;
// Set 'direct' if we can modify the input frame in-place. Otherwise we
// need to retrieve a new frame from the output link.
int direct = av_frame_is_writable(in) && !ctx->is_disabled;
if (direct) {
out = in;
} else {
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);
}
// Now we've got the input and output frames (which may be the same frame)
// perform the filtering with our custom function.
normalize(s, in, out);
if (ctx->is_disabled) {
av_frame_free(&out);
return ff_filter_frame(outlink, in);
}
if (!direct)
av_frame_free(&in);
return ff_filter_frame(outlink, out);
}
static const AVFilterPad inputs[] = {
{
.name = "default",
.type = AVMEDIA_TYPE_VIDEO,
.filter_frame = filter_frame,
.config_props = config_input,
},
{ NULL }
};
static const AVFilterPad outputs[] = {
{
.name = "default",
.type = AVMEDIA_TYPE_VIDEO,
},
{ NULL }
};
AVFilter ff_vf_normalize = {
.name = "normalize",
.description = NULL_IF_CONFIG_SMALL("Normalize RGB video."),
.priv_size = sizeof(NormalizeContext),
.priv_class = &normalize_class,
.uninit = uninit,
.query_formats = query_formats,
.inputs = inputs,
.outputs = outputs,
};