2 * Copyright (c) 2017 Richard Ling
4 * This file is part of FFmpeg.
6 * FFmpeg is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU Lesser General Public
8 * License as published by the Free Software Foundation; either
9 * version 2.1 of the License, or (at your option) any later version.
11 * FFmpeg is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * Lesser General Public License for more details.
16 * You should have received a copy of the GNU Lesser General Public
17 * License along with FFmpeg; if not, write to the Free Software
18 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
22 * Normalize RGB video (aka histogram stretching, contrast stretching).
23 * See: https://en.wikipedia.org/wiki/Normalization_(image_processing)
25 * For each channel of each frame, the filter computes the input range and maps
26 * it linearly to the user-specified output range. The output range defaults
27 * to the full dynamic range from pure black to pure white.
29 * Naively maximising the dynamic range of each frame of video in isolation
30 * may cause flickering (rapid changes in brightness of static objects in the
31 * scene) when small dark or bright objects enter or leave the scene. This
32 * filter can apply temporal smoothing to the input range to reduce flickering.
33 * Temporal smoothing is similar to the auto-exposure (automatic gain control)
34 * on a video camera, which performs the same function; and, like a video
35 * camera, it may cause a period of over- or under-exposure of the video.
37 * The filter can normalize the R,G,B channels independently, which may cause
38 * color shifting, or link them together as a single channel, which prevents
39 * color shifting. More precisely, linked normalization preserves hue (as it's
40 * defined in HSV/HSL color spaces) while independent normalization does not.
41 * Independent normalization can be used to remove color casts, such as the
42 * blue cast from underwater video, restoring more natural colors. The filter
43 * can also combine independent and linked normalization in any ratio.
45 * Finally the overall strength of the filter can be adjusted, from no effect
46 * to full normalization.
48 * The 5 AVOptions are:
49 * blackpt, Colors which define the output range. The minimum input value
50 * whitept is mapped to the blackpt. The maximum input value is mapped to
51 * the whitept. The defaults are black and white respectively.
52 * Specifying white for blackpt and black for whitept will give
53 * color-inverted, normalized video. Shades of grey can be used
54 * to reduce the dynamic range (contrast). Specifying saturated
55 * colors here can create some interesting effects.
57 * smoothing The amount of temporal smoothing, expressed in frames (>=0).
58 * the minimum and maximum input values of each channel are
59 * smoothed using a rolling average over the current frame and
60 * that many previous frames of video. Defaults to 0 (no temporal
64 * Controls the ratio of independent (color shifting) channel
65 * normalization to linked (color preserving) normalization. 0.0
66 * is fully linked, 1.0 is fully independent. Defaults to fully
69 * strength Overall strength of the filter. 1.0 is full strength. 0.0 is
70 * a rather expensive no-op. Values in between can give a gentle
71 * boost to low-contrast video without creating an artificial
72 * over-processed look. The default is full strength.
75 #include "libavutil/imgutils.h"
76 #include "libavutil/opt.h"
77 #include "libavutil/pixdesc.h"
83 typedef struct NormalizeContext {
86 // Storage for the corresponding AVOptions
93 int co[4]; // Offsets to R,G,B,A bytes respectively in each pixel
94 int num_components; // Number of components in the pixel format
95 int history_len; // Number of frames to average; based on smoothing factor
96 int frame_num; // Increments on each frame, starting from 0.
98 // Per-extremum, per-channel history, for temporal smoothing.
100 uint8_t *history; // History entries.
101 uint32_t history_sum; // Sum of history entries.
102 } min[3], max[3]; // Min and max for each channel in {R,G,B}.
103 uint8_t *history_mem; // Single allocation for above history entries
107 #define OFFSET(x) offsetof(NormalizeContext, x)
108 #define FLAGS AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_FILTERING_PARAM
110 static const AVOption normalize_options[] = {
111 { "blackpt", "output color to which darkest input color is mapped", OFFSET(blackpt), AV_OPT_TYPE_COLOR, { .str = "black" }, CHAR_MIN, CHAR_MAX, FLAGS },
112 { "whitept", "output color to which brightest input color is mapped", OFFSET(whitept), AV_OPT_TYPE_COLOR, { .str = "white" }, CHAR_MIN, CHAR_MAX, FLAGS },
113 { "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 },
114 { "independence", "proportion of independent to linked channel normalization", OFFSET(independence), AV_OPT_TYPE_FLOAT, {.dbl=1.0}, 0.0, 1.0, FLAGS },
115 { "strength", "strength of filter, from no effect to full normalization", OFFSET(strength), AV_OPT_TYPE_FLOAT, {.dbl=1.0}, 0.0, 1.0, FLAGS },
119 AVFILTER_DEFINE_CLASS(normalize);
121 // This function is the main guts of the filter. Normalizes the input frame
122 // into the output frame. The frames are known to have the same dimensions
124 static void normalize(NormalizeContext *s, AVFrame *in, AVFrame *out)
126 // Per-extremum, per-channel local variables.
128 uint8_t in; // Original input byte value for this frame.
129 float smoothed; // Smoothed input value [0,255].
130 float out; // Output value [0,255].
131 } min[3], max[3]; // Min and max for each channel in {R,G,B}.
133 float rgb_min_smoothed; // Min input range for linked normalization
134 float rgb_max_smoothed; // Max input range for linked normalization
135 uint8_t lut[3][256]; // Lookup table
138 // First, scan the input frame to find, for each channel, the minimum
139 // (min.in) and maximum (max.in) values present in the channel.
140 for (c = 0; c < 3; c++)
141 min[c].in = max[c].in = in->data[0][s->co[c]];
142 for (y = 0; y < in->height; y++) {
143 uint8_t *inp = in->data[0] + y * in->linesize[0];
144 uint8_t *outp = out->data[0] + y * out->linesize[0];
145 for (x = 0; x < in->width; x++) {
146 for (c = 0; c < 3; c++) {
147 min[c].in = FFMIN(min[c].in, inp[s->co[c]]);
148 max[c].in = FFMAX(max[c].in, inp[s->co[c]]);
150 inp += s->num_components;
151 outp += s->num_components;
155 // Next, for each channel, push min.in and max.in into their respective
156 // histories, to determine the min.smoothed and max.smoothed for this frame.
158 int history_idx = s->frame_num % s->history_len;
159 // Assume the history is not yet full; num_history_vals is the number
160 // of frames received so far including the current frame.
161 int num_history_vals = s->frame_num + 1;
162 if (s->frame_num >= s->history_len) {
163 //The history is full; drop oldest value and cap num_history_vals.
164 for (c = 0; c < 3; c++) {
165 s->min[c].history_sum -= s->min[c].history[history_idx];
166 s->max[c].history_sum -= s->max[c].history[history_idx];
168 num_history_vals = s->history_len;
170 // For each extremum, update history_sum and calculate smoothed value
171 // as the rolling average of the history entries.
172 for (c = 0; c < 3; c++) {
173 s->min[c].history_sum += (s->min[c].history[history_idx] = min[c].in);
174 min[c].smoothed = s->min[c].history_sum / (float)num_history_vals;
175 s->max[c].history_sum += (s->max[c].history[history_idx] = max[c].in);
176 max[c].smoothed = s->max[c].history_sum / (float)num_history_vals;
180 // Determine the input range for linked normalization. This is simply the
181 // minimum of the per-channel minimums, and the maximum of the per-channel
183 rgb_min_smoothed = FFMIN3(min[0].smoothed, min[1].smoothed, min[2].smoothed);
184 rgb_max_smoothed = FFMAX3(max[0].smoothed, max[1].smoothed, max[2].smoothed);
186 // Now, process each channel to determine the input and output range and
187 // build the lookup tables.
188 for (c = 0; c < 3; c++) {
190 // Adjust the input range for this channel [min.smoothed,max.smoothed]
191 // by mixing in the correct proportion of the linked normalization
192 // input range [rgb_min_smoothed,rgb_max_smoothed].
193 min[c].smoothed = (min[c].smoothed * s->independence)
194 + (rgb_min_smoothed * (1.0f - s->independence));
195 max[c].smoothed = (max[c].smoothed * s->independence)
196 + (rgb_max_smoothed * (1.0f - s->independence));
198 // Calculate the output range [min.out,max.out] as a ratio of the full-
199 // strength output range [blackpt,whitept] and the original input range
200 // [min.in,max.in], based on the user-specified filter strength.
201 min[c].out = (s->blackpt[c] * s->strength)
202 + (min[c].in * (1.0f - s->strength));
203 max[c].out = (s->whitept[c] * s->strength)
204 + (max[c].in * (1.0f - s->strength));
206 // Now, build a lookup table which linearly maps the adjusted input range
207 // [min.smoothed,max.smoothed] to the output range [min.out,max.out].
208 // Perform the linear interpolation for each x:
209 // lut[x] = (int)(float(x - min.smoothed) * scale + max.out + 0.5)
210 // where scale = (max.out - min.out) / (max.smoothed - min.smoothed)
211 if (min[c].smoothed == max[c].smoothed) {
212 // There is no dynamic range to expand. No mapping for this channel.
213 for (in_val = min[c].in; in_val <= max[c].in; in_val++)
214 lut[c][in_val] = min[c].out;
216 // We must set lookup values for all values in the original input
217 // range [min.in,max.in]. Since the original input range may be
218 // larger than [min.smoothed,max.smoothed], some output values may
219 // fall outside the [0,255] dynamic range. We need to clamp them.
220 float scale = (max[c].out - min[c].out) / (max[c].smoothed - min[c].smoothed);
221 for (in_val = min[c].in; in_val <= max[c].in; in_val++) {
222 int out_val = (in_val - min[c].smoothed) * scale + min[c].out + 0.5f;
223 out_val = FFMAX(out_val, 0);
224 out_val = FFMIN(out_val, 255);
225 lut[c][in_val] = out_val;
230 // Finally, process the pixels of the input frame using the lookup tables.
231 for (y = 0; y < in->height; y++) {
232 uint8_t *inp = in->data[0] + y * in->linesize[0];
233 uint8_t *outp = out->data[0] + y * out->linesize[0];
234 for (x = 0; x < in->width; x++) {
235 for (c = 0; c < 3; c++)
236 outp[s->co[c]] = lut[c][inp[s->co[c]]];
237 if (s->num_components == 4)
239 outp[s->co[3]] = inp[s->co[3]];
240 inp += s->num_components;
241 outp += s->num_components;
248 // Now we define all the functions accessible from the ff_vf_normalize class,
249 // which is ffmpeg's interface to our filter. See doc/filter_design.txt and
250 // doc/writing_filters.txt for descriptions of what these interface functions
251 // are expected to do.
253 // Set the pixel formats that our filter supports. We should be able to process
254 // any 8-bit RGB formats. 16-bit support might be useful one day.
255 static int query_formats(AVFilterContext *ctx)
257 static const enum AVPixelFormat pixel_fmts[] = {
270 // According to filter_design.txt, using ff_set_common_formats() this way
271 // ensures the pixel formats of the input and output will be the same. That
272 // saves a bit of effort possibly needing to handle format conversions.
273 AVFilterFormats *formats = ff_make_format_list(pixel_fmts);
275 return AVERROR(ENOMEM);
276 return ff_set_common_formats(ctx, formats);
279 // At this point we know the pixel format used for both input and output. We
280 // can also access the frame rate of the input video and allocate some memory
282 static int config_input(AVFilterLink *inlink)
284 NormalizeContext *s = inlink->dst->priv;
285 // Store offsets to R,G,B,A bytes respectively in each pixel
286 const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(inlink->format);
289 for (c = 0; c < 4; ++c)
290 s->co[c] = desc->comp[c].offset;
291 s->num_components = desc->nb_components;
292 // Convert smoothing value to history_len (a count of frames to average,
293 // must be at least 1). Currently this is a direct assignment, but the
294 // smoothing value was originally envisaged as a number of seconds. In
295 // future it would be nice to set history_len using a number of seconds,
296 // but VFR video is currently an obstacle to doing so.
297 s->history_len = s->smoothing + 1;
298 // Allocate the history buffers -- there are 6 -- one for each extrema.
299 // s->smoothing is limited to INT_MAX/8, so that (s->history_len * 6)
300 // can't overflow on 32bit causing a too-small allocation.
301 s->history_mem = av_malloc(s->history_len * 6);
302 if (s->history_mem == NULL)
303 return AVERROR(ENOMEM);
305 for (c = 0; c < 3; c++) {
306 s->min[c].history = s->history_mem + (c*2) * s->history_len;
307 s->max[c].history = s->history_mem + (c*2+1) * s->history_len;
312 // Free any memory allocations here
313 static av_cold void uninit(AVFilterContext *ctx)
315 NormalizeContext *s = ctx->priv;
317 av_freep(&s->history_mem);
320 // This function is pretty much standard from doc/writing_filters.txt. It
321 // tries to do in-place filtering where possible, only allocating a new output
322 // frame when absolutely necessary.
323 static int filter_frame(AVFilterLink *inlink, AVFrame *in)
325 AVFilterContext *ctx = inlink->dst;
326 AVFilterLink *outlink = ctx->outputs[0];
327 NormalizeContext *s = ctx->priv;
329 // Set 'direct' if we can modify the input frame in-place. Otherwise we
330 // need to retrieve a new frame from the output link.
331 int direct = av_frame_is_writable(in) && !ctx->is_disabled;
336 out = ff_get_video_buffer(outlink, outlink->w, outlink->h);
339 return AVERROR(ENOMEM);
341 av_frame_copy_props(out, in);
344 // Now we've got the input and output frames (which may be the same frame)
345 // perform the filtering with our custom function.
346 normalize(s, in, out);
348 if (ctx->is_disabled) {
350 return ff_filter_frame(outlink, in);
356 return ff_filter_frame(outlink, out);
359 static const AVFilterPad inputs[] = {
362 .type = AVMEDIA_TYPE_VIDEO,
363 .filter_frame = filter_frame,
364 .config_props = config_input,
369 static const AVFilterPad outputs[] = {
372 .type = AVMEDIA_TYPE_VIDEO,
377 AVFilter ff_vf_normalize = {
379 .description = NULL_IF_CONFIG_SMALL("Normalize RGB video."),
380 .priv_size = sizeof(NormalizeContext),
381 .priv_class = &normalize_class,
383 .query_formats = query_formats,