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/* |
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* Copyright (c) 2017 Richard Ling |
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* |
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* This file is part of FFmpeg. |
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* |
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* FFmpeg is free software; you can redistribute it and/or |
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* modify it under the terms of the GNU Lesser General Public |
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* License as published by the Free Software Foundation; either |
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* version 2.1 of the License, or (at your option) any later version. |
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* |
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* FFmpeg is distributed in the hope that it will be useful, |
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* but WITHOUT ANY WARRANTY; without even the implied warranty of |
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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* Lesser General Public License for more details. |
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* |
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* You should have received a copy of the GNU Lesser General Public |
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* License along with FFmpeg; if not, write to the Free Software |
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
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*/ |
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/* |
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* Normalize RGB video (aka histogram stretching, contrast stretching). |
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* See: https://en.wikipedia.org/wiki/Normalization_(image_processing) |
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* |
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* For each channel of each frame, the filter computes the input range and maps |
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* it linearly to the user-specified output range. The output range defaults |
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* to the full dynamic range from pure black to pure white. |
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* |
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* Naively maximising the dynamic range of each frame of video in isolation |
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* may cause flickering (rapid changes in brightness of static objects in the |
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* scene) when small dark or bright objects enter or leave the scene. This |
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* filter can apply temporal smoothing to the input range to reduce flickering. |
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* Temporal smoothing is similar to the auto-exposure (automatic gain control) |
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* on a video camera, which performs the same function; and, like a video |
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* camera, it may cause a period of over- or under-exposure of the video. |
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* |
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* The filter can normalize the R,G,B channels independently, which may cause |
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* color shifting, or link them together as a single channel, which prevents |
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* color shifting. More precisely, linked normalization preserves hue (as it's |
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* defined in HSV/HSL color spaces) while independent normalization does not. |
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* Independent normalization can be used to remove color casts, such as the |
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* blue cast from underwater video, restoring more natural colors. The filter |
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* can also combine independent and linked normalization in any ratio. |
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* |
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* Finally the overall strength of the filter can be adjusted, from no effect |
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* to full normalization. |
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* |
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* The 5 AVOptions are: |
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* blackpt, Colors which define the output range. The minimum input value |
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* whitept is mapped to the blackpt. The maximum input value is mapped to |
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* the whitept. The defaults are black and white respectively. |
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* Specifying white for blackpt and black for whitept will give |
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* color-inverted, normalized video. Shades of grey can be used |
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* to reduce the dynamic range (contrast). Specifying saturated |
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* colors here can create some interesting effects. |
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* |
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* smoothing The amount of temporal smoothing, expressed in frames (>=0). |
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* the minimum and maximum input values of each channel are |
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* smoothed using a rolling average over the current frame and |
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* that many previous frames of video. Defaults to 0 (no temporal |
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* smoothing). |
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* |
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* independence |
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* Controls the ratio of independent (color shifting) channel |
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* normalization to linked (color preserving) normalization. 0.0 |
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* is fully linked, 1.0 is fully independent. Defaults to fully |
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* independent. |
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* |
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* strength Overall strength of the filter. 1.0 is full strength. 0.0 is |
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* a rather expensive no-op. Values in between can give a gentle |
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* boost to low-contrast video without creating an artificial |
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* over-processed look. The default is full strength. |
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*/ |
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#include "libavutil/imgutils.h" |
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#include "libavutil/opt.h" |
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#include "libavutil/pixdesc.h" |
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#include "avfilter.h" |
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#include "formats.h" |
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#include "internal.h" |
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#include "video.h" |
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typedef struct NormalizeContext { |
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const AVClass *class; |
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// Storage for the corresponding AVOptions |
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uint8_t blackpt[4]; |
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uint8_t whitept[4]; |
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int smoothing; |
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float independence; |
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float strength; |
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int co[4]; // Offsets to R,G,B,A bytes respectively in each pixel |
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int num_components; // Number of components in the pixel format |
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int history_len; // Number of frames to average; based on smoothing factor |
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int frame_num; // Increments on each frame, starting from 0. |
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// Per-extremum, per-channel history, for temporal smoothing. |
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struct { |
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uint8_t *history; // History entries. |
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uint32_t history_sum; // Sum of history entries. |
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} min[3], max[3]; // Min and max for each channel in {R,G,B}. |
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uint8_t *history_mem; // Single allocation for above history entries |
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} NormalizeContext; |
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#define OFFSET(x) offsetof(NormalizeContext, x) |
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#define FLAGS AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_FILTERING_PARAM |
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static const AVOption normalize_options[] = { |
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{ "blackpt", "output color to which darkest input color is mapped", OFFSET(blackpt), AV_OPT_TYPE_COLOR, { .str = "black" }, CHAR_MIN, CHAR_MAX, FLAGS }, |
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{ "whitept", "output color to which brightest input color is mapped", OFFSET(whitept), AV_OPT_TYPE_COLOR, { .str = "white" }, CHAR_MIN, CHAR_MAX, FLAGS }, |
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{ "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 }, |
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{ "independence", "proportion of independent to linked channel normalization", OFFSET(independence), AV_OPT_TYPE_FLOAT, {.dbl=1.0}, 0.0, 1.0, FLAGS }, |
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{ "strength", "strength of filter, from no effect to full normalization", OFFSET(strength), AV_OPT_TYPE_FLOAT, {.dbl=1.0}, 0.0, 1.0, FLAGS }, |
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{ NULL } |
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}; |
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AVFILTER_DEFINE_CLASS(normalize); |
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// This function is the main guts of the filter. Normalizes the input frame |
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// into the output frame. The frames are known to have the same dimensions |
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// and pixel format. |
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static void normalize(NormalizeContext *s, AVFrame *in, AVFrame *out) |
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{ |
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// Per-extremum, per-channel local variables. |
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struct { |
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uint8_t in; // Original input byte value for this frame. |
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float smoothed; // Smoothed input value [0,255]. |
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float out; // Output value [0,255]. |
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} min[3], max[3]; // Min and max for each channel in {R,G,B}. |
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float rgb_min_smoothed; // Min input range for linked normalization |
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float rgb_max_smoothed; // Max input range for linked normalization |
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uint8_t lut[3][256]; // Lookup table |
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int x, y, c; |
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// First, scan the input frame to find, for each channel, the minimum |
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// (min.in) and maximum (max.in) values present in the channel. |
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for (c = 0; c < 3; c++) |
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min[c].in = max[c].in = in->data[0][s->co[c]]; |
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for (y = 0; y < in->height; y++) { |
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uint8_t *inp = in->data[0] + y * in->linesize[0]; |
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uint8_t *outp = out->data[0] + y * out->linesize[0]; |
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for (x = 0; x < in->width; x++) { |
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for (c = 0; c < 3; c++) { |
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min[c].in = FFMIN(min[c].in, inp[s->co[c]]); |
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max[c].in = FFMAX(max[c].in, inp[s->co[c]]); |
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} |
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inp += s->num_components; |
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outp += s->num_components; |
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} |
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} |
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// Next, for each channel, push min.in and max.in into their respective |
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// histories, to determine the min.smoothed and max.smoothed for this frame. |
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{ |
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int history_idx = s->frame_num % s->history_len; |
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// Assume the history is not yet full; num_history_vals is the number |
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// of frames received so far including the current frame. |
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int num_history_vals = s->frame_num + 1; |
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if (s->frame_num >= s->history_len) { |
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//The history is full; drop oldest value and cap num_history_vals. |
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for (c = 0; c < 3; c++) { |
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s->min[c].history_sum -= s->min[c].history[history_idx]; |
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s->max[c].history_sum -= s->max[c].history[history_idx]; |
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} |
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num_history_vals = s->history_len; |
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} |
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// For each extremum, update history_sum and calculate smoothed value |
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// as the rolling average of the history entries. |
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for (c = 0; c < 3; c++) { |
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s->min[c].history_sum += (s->min[c].history[history_idx] = min[c].in); |
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min[c].smoothed = s->min[c].history_sum / (float)num_history_vals; |
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s->max[c].history_sum += (s->max[c].history[history_idx] = max[c].in); |
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max[c].smoothed = s->max[c].history_sum / (float)num_history_vals; |
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} |
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} |
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// Determine the input range for linked normalization. This is simply the |
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// minimum of the per-channel minimums, and the maximum of the per-channel |
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// maximums. |
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rgb_min_smoothed = FFMIN3(min[0].smoothed, min[1].smoothed, min[2].smoothed); |
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rgb_max_smoothed = FFMAX3(max[0].smoothed, max[1].smoothed, max[2].smoothed); |
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// Now, process each channel to determine the input and output range and |
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// build the lookup tables. |
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for (c = 0; c < 3; c++) { |
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int in_val; |
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// Adjust the input range for this channel [min.smoothed,max.smoothed] |
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// by mixing in the correct proportion of the linked normalization |
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// input range [rgb_min_smoothed,rgb_max_smoothed]. |
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min[c].smoothed = (min[c].smoothed * s->independence) |
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+ (rgb_min_smoothed * (1.0f - s->independence)); |
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max[c].smoothed = (max[c].smoothed * s->independence) |
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+ (rgb_max_smoothed * (1.0f - s->independence)); |
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// Calculate the output range [min.out,max.out] as a ratio of the full- |
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// strength output range [blackpt,whitept] and the original input range |
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// [min.in,max.in], based on the user-specified filter strength. |
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min[c].out = (s->blackpt[c] * s->strength) |
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+ (min[c].in * (1.0f - s->strength)); |
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max[c].out = (s->whitept[c] * s->strength) |
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+ (max[c].in * (1.0f - s->strength)); |
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// Now, build a lookup table which linearly maps the adjusted input range |
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// [min.smoothed,max.smoothed] to the output range [min.out,max.out]. |
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// Perform the linear interpolation for each x: |
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// lut[x] = (int)(float(x - min.smoothed) * scale + max.out + 0.5) |
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// where scale = (max.out - min.out) / (max.smoothed - min.smoothed) |
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if (min[c].smoothed == max[c].smoothed) { |
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// There is no dynamic range to expand. No mapping for this channel. |
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for (in_val = min[c].in; in_val <= max[c].in; in_val++) |
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lut[c][in_val] = min[c].out; |
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} else { |
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// We must set lookup values for all values in the original input |
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// range [min.in,max.in]. Since the original input range may be |
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// larger than [min.smoothed,max.smoothed], some output values may |
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// fall outside the [0,255] dynamic range. We need to clamp them. |
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float scale = (max[c].out - min[c].out) / (max[c].smoothed - min[c].smoothed); |
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for (in_val = min[c].in; in_val <= max[c].in; in_val++) { |
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int out_val = (in_val - min[c].smoothed) * scale + min[c].out + 0.5f; |
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out_val = FFMAX(out_val, 0); |
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out_val = FFMIN(out_val, 255); |
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lut[c][in_val] = out_val; |
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} |
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} |
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} |
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// Finally, process the pixels of the input frame using the lookup tables. |
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for (y = 0; y < in->height; y++) { |
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uint8_t *inp = in->data[0] + y * in->linesize[0]; |
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uint8_t *outp = out->data[0] + y * out->linesize[0]; |
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for (x = 0; x < in->width; x++) { |
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for (c = 0; c < 3; c++) |
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outp[s->co[c]] = lut[c][inp[s->co[c]]]; |
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if (s->num_components == 4) |
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// Copy alpha as-is. |
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outp[s->co[3]] = inp[s->co[3]]; |
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inp += s->num_components; |
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outp += s->num_components; |
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} |
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} |
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s->frame_num++; |
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} |
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// Now we define all the functions accessible from the ff_vf_normalize class, |
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// which is ffmpeg's interface to our filter. See doc/filter_design.txt and |
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// doc/writing_filters.txt for descriptions of what these interface functions |
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// are expected to do. |
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// Set the pixel formats that our filter supports. We should be able to process |
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// any 8-bit RGB formats. 16-bit support might be useful one day. |
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static int query_formats(AVFilterContext *ctx) |
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{ |
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static const enum AVPixelFormat pixel_fmts[] = { |
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AV_PIX_FMT_RGB24, |
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AV_PIX_FMT_BGR24, |
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AV_PIX_FMT_ARGB, |
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AV_PIX_FMT_RGBA, |
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AV_PIX_FMT_ABGR, |
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AV_PIX_FMT_BGRA, |
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AV_PIX_FMT_0RGB, |
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AV_PIX_FMT_RGB0, |
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AV_PIX_FMT_0BGR, |
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AV_PIX_FMT_BGR0, |
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AV_PIX_FMT_NONE |
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}; |
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// According to filter_design.txt, using ff_set_common_formats() this way |
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// ensures the pixel formats of the input and output will be the same. That |
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// saves a bit of effort possibly needing to handle format conversions. |
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AVFilterFormats *formats = ff_make_format_list(pixel_fmts); |
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if (!formats) |
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return AVERROR(ENOMEM); |
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return ff_set_common_formats(ctx, formats); |
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} |
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// At this point we know the pixel format used for both input and output. We |
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// can also access the frame rate of the input video and allocate some memory |
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// appropriately |
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static int config_input(AVFilterLink *inlink) |
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{ |
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NormalizeContext *s = inlink->dst->priv; |
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// Store offsets to R,G,B,A bytes respectively in each pixel |
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const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(inlink->format); |
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int c; |
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for (c = 0; c < 4; ++c) |
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s->co[c] = desc->comp[c].offset; |
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s->num_components = desc->nb_components; |
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// Convert smoothing value to history_len (a count of frames to average, |
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// must be at least 1). Currently this is a direct assignment, but the |
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// smoothing value was originally envisaged as a number of seconds. In |
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// future it would be nice to set history_len using a number of seconds, |
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// but VFR video is currently an obstacle to doing so. |
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s->history_len = s->smoothing + 1; |
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// Allocate the history buffers -- there are 6 -- one for each extrema. |
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// s->smoothing is limited to INT_MAX/8, so that (s->history_len * 6) |
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// can't overflow on 32bit causing a too-small allocation. |
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s->history_mem = av_malloc(s->history_len * 6); |
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if (s->history_mem == NULL) |
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return AVERROR(ENOMEM); |
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for (c = 0; c < 3; c++) { |
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s->min[c].history = s->history_mem + (c*2) * s->history_len; |
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s->max[c].history = s->history_mem + (c*2+1) * s->history_len; |
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} |
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return 0; |
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} |
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// Free any memory allocations here |
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static av_cold void uninit(AVFilterContext *ctx) |
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{ |
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NormalizeContext *s = ctx->priv; |
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av_freep(&s->history_mem); |
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} |
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// This function is pretty much standard from doc/writing_filters.txt. It |
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// tries to do in-place filtering where possible, only allocating a new output |
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// frame when absolutely necessary. |
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static int filter_frame(AVFilterLink *inlink, AVFrame *in) |
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{ |
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AVFilterContext *ctx = inlink->dst; |
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AVFilterLink *outlink = ctx->outputs[0]; |
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NormalizeContext *s = ctx->priv; |
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AVFrame *out; |
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// Set 'direct' if we can modify the input frame in-place. Otherwise we |
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// need to retrieve a new frame from the output link. |
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int direct = av_frame_is_writable(in) && !ctx->is_disabled; |
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if (direct) { |
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out = in; |
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} else { |
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out = ff_get_video_buffer(outlink, outlink->w, outlink->h); |
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if (!out) { |
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av_frame_free(&in); |
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return AVERROR(ENOMEM); |
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|
} |
|
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|
av_frame_copy_props(out, in); |
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} |
|
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|
|
|
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// 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, |
|
|
|
}; |
Richard Ling
Paul B Mahol
8 years ago