filters.c File Reference

#include <math.h>
#include <stdbool.h>
#include <libavutil/attributes.h>
#include <libavutil/avassert.h>
#include <libavutil/mem.h>
#include "filters.h"

Go to the source code of this file.

Data Structures
struct	SwsFilterFunction

Macros
#define	RADIUS_MAX   10.0

Typedefs
typedef double(*	SwsFilterKernel) (double x, const double *params)

Functions
static double	scaler_sample (const SwsFilterFunction *f, double x)
static void	compute_row (SwsFilterWeights *f, const SwsFilterFunction *fun, double radius, double ratio_inv, double stretch_inv, int dst_pos, double *tmp)
static void	sws_filter_free (AVRefStructOpaque opaque, void *obj)
static bool	validate_params (const SwsFilterFunction *fun, SwsScaler scaler)
static double	filter_radius (const SwsFilterFunction *fun)
int	ff_sws_filter_generate (void *log, const SwsFilterParams *params, SwsFilterWeights **out)
	Generate a filter kernel for the given parameters. More...
static av_unused double	box (double x, const double *params)
static av_unused double	triangle (double x, const double *params)
static av_unused double	cosine (double x, const double *params)
static av_unused double	hann (double x, const double *params)
static av_unused double	hamming (double x, const double *params)
static av_unused double	welch (double x, const double *params)
static av_unused double	bessel_i0 (double x)
static av_unused double	kaiser (double x, const double *params)
static av_unused double	blackman (double x, const double *params)
static av_unused double	bohman (double x, const double *params)
static av_unused double	gaussian (double x, const double *params)
static av_unused double	quadratic (double x, const double *params)
static av_unused double	sinc (double x, const double *params)
static av_unused double	jinc (double x, const double *params)
static av_unused double	sphinx (double x, const double *params)
static av_unused double	cubic (double x, const double *params)
static double	spline_coeff (double a, double b, double c, double d, double x)
static av_unused double	spline (double x, const double *params)

Variables
static const SwsFilterFunction	filter_functions [SWS_SCALE_NB]

Macro Definition Documentation

RADIUS_MAX

#define RADIUS_MAX   10.0

Definition at line 35 of file filters.c.

Typedef Documentation

SwsFilterKernel

typedef double(* SwsFilterKernel) (double x, const double *params)

Definition at line 38 of file filters.c.

Function Documentation

scaler_sample()

static double scaler_sample ( const SwsFilterFunction *  f, double  x  )

static

Definition at line 50 of file filters.c.

Referenced by compute_row(), and filter_radius().

compute_row()

static void compute_row ( SwsFilterWeights *  f, const SwsFilterFunction *  fun, double  radius, double  ratio_inv, double  stretch_inv, int  dst_pos, double *  tmp  )

static

Explanation of the 0.5 offsets: Normally, pixel samples are assumed to be representative of the center of their containing area; e.g. for a 2x2 image, the samples are located at {0.5, 1.5}^2. However, with integer indexing, we round sample positions down (0-based indexing). So the (0, 0) sample is actually located at (0.5, 0.5) and represents the entire square from (0,0) to (1,1). When normalizing between different image sizes, we therefore need to add/subtract off these 0.5 offsets.

Generate raw filter weights with maximum precision. Sum the positive and negative weights separately to avoid catastrophic cancellation. This summation order should already give the best precision because abs(w) is monotonically decreasing

Definition at line 62 of file filters.c.

Referenced by ff_sws_filter_generate().

sws_filter_free()

static void sws_filter_free ( AVRefStructOpaque  opaque, void *  obj  )

static

Definition at line 136 of file filters.c.

Referenced by ff_sws_filter_generate().

validate_params()

static bool validate_params ( const SwsFilterFunction *  fun, SwsScaler  scaler  )

static

Definition at line 143 of file filters.c.

Referenced by ff_sws_filter_generate().

filter_radius()

static double filter_radius ( const SwsFilterFunction *  fun )

static

Definition at line 157 of file filters.c.

Referenced by ff_sws_filter_generate().

ff_sws_filter_generate()

int ff_sws_filter_generate	(	void *	log_ctx,
		const SwsFilterParams *	params,
		SwsFilterWeights **	out
	)

Generate a filter kernel for the given parameters.

The generated filter is allocated as a refstruct and must be unref'd by the caller.

Returns 0 or a negative error code. In particular, this may return:

• AVERROR(ENOMEM) if memory allocation fails.
• AVERROR(EINVAL) if the provided parameters are invalid (e.g. out of range).
• AVERROR(ENOTSUP) if the generated filter would exceed SWS_FILTER_SIZE_MAX.

SWS_SCALE_AREA is a pseudo-filter that is equivalent to bilinear filtering for upscaling (since bilinear just evenly mixes samples according to the relative distance), and equivalent to (anti-aliased) point sampling for downscaling.

Definition at line 183 of file filters.c.

Referenced by check_filter().

box()

static av_unused double box ( double  x, const double *  params  )

static

Definition at line 296 of file filters.c.

Referenced by colormap_insert(), compute_box_stats(), ddagrab_request_frame(), drawbox_vaapi_filter_frame(), filter_frame(), get_next_box_id_to_split(), get_next_color(), get_palette_frame(), load_colormap(), split_box(), and subshift().

triangle()

static av_unused double triangle ( double  x, const double *  params  )

static

Definition at line 301 of file filters.c.

cosine()

static av_unused double cosine ( double  x, const double *  params  )

static

Definition at line 306 of file filters.c.

Referenced by set_ap(), set_hp(), and set_lp().

hann()

static av_unused double hann ( double  x, const double *  params  )

static

Definition at line 311 of file filters.c.

hamming()

static av_unused double hamming ( double  x, const double *  params  )

static

Definition at line 316 of file filters.c.

welch()

static av_unused double welch ( double  x, const double *  params  )

static

Definition at line 321 of file filters.c.

bessel_i0()

static av_unused double bessel_i0 ( double  x )

static

Definition at line 326 of file filters.c.

Referenced by kaiser().

kaiser()

static av_unused double kaiser ( double  x, const double *  params  )

static

Definition at line 340 of file filters.c.

blackman()

static av_unused double blackman ( double  x, const double *  params  )

static

Definition at line 347 of file filters.c.

bohman()

static av_unused double bohman ( double  x, const double *  params  )

static

Definition at line 355 of file filters.c.

gaussian()

static av_unused double gaussian ( double  x, const double *  params  )

static

Definition at line 361 of file filters.c.

quadratic()

static av_unused double quadratic ( double  x, const double *  params  )

static

Definition at line 366 of file filters.c.

sinc()

static av_unused double sinc ( double  x, const double *  params  )

static

Definition at line 375 of file filters.c.

jinc()

static av_unused double jinc ( double  x, const double *  params  )

static

Definition at line 383 of file filters.c.

sphinx()

static av_unused double sphinx ( double  x, const double *  params  )

static

Definition at line 391 of file filters.c.

cubic()

static av_unused double cubic ( double  x, const double *  params  )

static

Definition at line 399 of file filters.c.

spline_coeff()

static double spline_coeff ( double  a, double  b, double  c, double  d, double  x  )

static

Definition at line 417 of file filters.c.

Referenced by spline().

spline()

static av_unused double spline ( double  x, const double *  params  )

static

Definition at line 430 of file filters.c.

Variable Documentation

filter_functions

static const SwsFilterFunction filter_functions

static

Initial value:

= {
    [SWS_SCALE_BILINEAR]    = { "bilinear",     1.0, triangle },
    [SWS_SCALE_BICUBIC]     = { "bicubic",      2.0, cubic, .params = { 0.0, 0.6 } },
    [SWS_SCALE_POINT]       = { "point",        0.5, box },
    [SWS_SCALE_GAUSSIAN]    = { "gaussian",     4.0, gaussian, .params = { 3.0 } },
    [SWS_SCALE_SINC]        = { "sinc",         RADIUS_MAX, sinc },
    [SWS_SCALE_LANCZOS]     = { "lanczos",      -1.0, sinc, sinc, .params = { 3.0 } },
    [SWS_SCALE_SPLINE]      = { "spline",       RADIUS_MAX, spline },
    
}

Definition at line 48 of file filters.c.

Referenced by ff_sws_filter_generate().