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exr: Add a gamma flag to exr loader to avoid banding

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This is needed to avoid banding artifacts when gammaing the picture.
Currently, if done with a video filter, the process is done on uints
instead of full float.

Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>
pull/101/head
Gonzalo Garramuno 10 years ago committed by Vittorio Giovara
parent d69d787dad
commit e0bb74a140
1 changed files with 110 additions and 7 deletions
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  1. 117
      libavcodec/exr.c

117
libavcodec/exr.c
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@ -27,12 +27,15 @@
* For more information on the OpenEXR format, visit:
* http://openexr.com/
*
* exr_flt2uint() and exr_halflt2uint() is credited to Reimar Döffinger
* exr_flt2uint() and exr_halflt2uint() is credited to Reimar Döffinger.
* exr_half2float() is credited to Aaftab Munshi, Dan Ginsburg, Dave Shreiner.
*/
#include <float.h>
#include <zlib.h>
#include "libavutil/imgutils.h"
#include "libavutil/intfloat.h"
#include "libavutil/opt.h"
#include "avcodec.h"
@ -106,8 +109,74 @@ typedef struct EXRContext {
EXRThreadData *thread_data;
const char *layer;
float gamma;
uint16_t gamma_table[65536];
} EXRContext;
/* -15 stored using a single precision bias of 127 */
#define HALF_FLOAT_MIN_BIASED_EXP_AS_SINGLE_FP_EXP 0x38000000
/* max exponent value in single precision that will be converted
* to Inf or Nan when stored as a half-float */
#define HALF_FLOAT_MAX_BIASED_EXP_AS_SINGLE_FP_EXP 0x47800000
/* 255 is the max exponent biased value */
#define FLOAT_MAX_BIASED_EXP (0xFF << 23)
#define HALF_FLOAT_MAX_BIASED_EXP (0x1F << 10)
/**
* Convert a half float as a uint16_t into a full float.
*
* @param hf half float as uint16_t
*
* @return float value
*/
static union av_intfloat32 exr_half2float(uint16_t hf)
{
unsigned int sign = (unsigned int) (hf >> 15);
unsigned int mantissa = (unsigned int) (hf & ((1 << 10) - 1));
unsigned int exp = (unsigned int) (hf & HALF_FLOAT_MAX_BIASED_EXP);
union av_intfloat32 f;
if (exp == HALF_FLOAT_MAX_BIASED_EXP) {
// we have a half-float NaN or Inf
// half-float NaNs will be converted to a single precision NaN
// half-float Infs will be converted to a single precision Inf
exp = FLOAT_MAX_BIASED_EXP;
if (mantissa)
mantissa = (1 << 23) - 1; // set all bits to indicate a NaN
} else if (exp == 0x0) {
// convert half-float zero/denorm to single precision value
if (mantissa) {
mantissa <<= 1;
exp = HALF_FLOAT_MIN_BIASED_EXP_AS_SINGLE_FP_EXP;
// check for leading 1 in denorm mantissa
while ((mantissa & (1 << 10))) {
// for every leading 0, decrement single precision exponent by 1
// and shift half-float mantissa value to the left
mantissa <<= 1;
exp -= (1 << 23);
}
// clamp the mantissa to 10-bits
mantissa &= ((1 << 10) - 1);
// shift left to generate single-precision mantissa of 23-bits
mantissa <<= 13;
}
} else {
// shift left to generate single-precision mantissa of 23-bits
mantissa <<= 13;
// generate single precision biased exponent value
exp = (exp << 13) + HALF_FLOAT_MIN_BIASED_EXP_AS_SINGLE_FP_EXP;
}
f.i = (sign << 31) | exp | mantissa;
return f;
}
/**
* Convert from 32-bit float as uint32_t to uint16_t.
*
@ -772,6 +841,7 @@ static int decode_block(AVCodecContext *avctx, void *tdata,
int axmax = (avctx->width - (s->xmax + 1)) * 2 * s->desc->nb_components;
int bxmin = s->xmin * 2 * s->desc->nb_components;
int i, x, buf_size = s->buf_size;
float one_gamma = 1.0f / s->gamma;
int ret;
line_offset = AV_RL64(s->gb.buffer + jobnr * 8);
@ -852,18 +922,30 @@ static int decode_block(AVCodecContext *avctx, void *tdata,
if (s->pixel_type == EXR_FLOAT) {
// 32-bit
for (x = 0; x < xdelta; x++) {
*ptr_x++ = exr_flt2uint(bytestream_get_le32(&r));
*ptr_x++ = exr_flt2uint(bytestream_get_le32(&g));
*ptr_x++ = exr_flt2uint(bytestream_get_le32(&b));
union av_intfloat32 t;
t.i = bytestream_get_le32(&r);
if (t.f > 0.0f) /* avoid negative values */
t.f = powf(t.f, one_gamma);
*ptr_x++ = exr_flt2uint(t.i);
t.i = bytestream_get_le32(&g);
if (t.f > 0.0f)
t.f = powf(t.f, one_gamma);
*ptr_x++ = exr_flt2uint(t.i);
t.i = bytestream_get_le32(&b);
if (t.f > 0.0f)
t.f = powf(t.f, one_gamma);
*ptr_x++ = exr_flt2uint(t.i);
if (channel_buffer[3])
*ptr_x++ = exr_flt2uint(bytestream_get_le32(&a));
}
} else {
// 16-bit
for (x = 0; x < xdelta; x++) {
*ptr_x++ = exr_halflt2uint(bytestream_get_le16(&r));
*ptr_x++ = exr_halflt2uint(bytestream_get_le16(&g));
*ptr_x++ = exr_halflt2uint(bytestream_get_le16(&b));
*ptr_x++ = s->gamma_table[bytestream_get_le16(&r)];
*ptr_x++ = s->gamma_table[bytestream_get_le16(&g)];
*ptr_x++ = s->gamma_table[bytestream_get_le16(&b)];
if (channel_buffer[3])
*ptr_x++ = exr_halflt2uint(bytestream_get_le16(&a));
}
@ -1263,6 +1345,9 @@ static int decode_frame(AVCodecContext *avctx, void *data,
static av_cold int decode_init(AVCodecContext *avctx)
{
EXRContext *s = avctx->priv_data;
uint32_t i;
union av_intfloat32 t;
float one_gamma = 1.0f / s->gamma;
s->avctx = avctx;
s->xmin = ~0;
@ -1281,6 +1366,22 @@ static av_cold int decode_init(AVCodecContext *avctx)
s->w = 0;
s->h = 0;
if (one_gamma > 0.9999f && one_gamma < 1.0001f) {
for (i = 0; i < 65536; ++i)
s->gamma_table[i] = exr_halflt2uint(i);
} else {
for (i = 0; i < 65536; ++i) {
t = exr_half2float(i);
/* If negative value we reuse half value */
if (t.f <= 0.0f) {
s->gamma_table[i] = exr_halflt2uint(i);
} else {
t.f = powf(t.f, one_gamma);
s->gamma_table[i] = exr_flt2uint(t.i);
}
}
}
// allocate thread data, used for non EXR_RAW compreesion types
s->thread_data = av_mallocz_array(avctx->thread_count, sizeof(EXRThreadData));
if (!s->thread_data)
@ -1323,6 +1424,8 @@ static av_cold int decode_end(AVCodecContext *avctx)
static const AVOption options[] = {
{ "layer", "Set the decoding layer", OFFSET(layer),
AV_OPT_TYPE_STRING, { .str = "" }, 0, 0, VD },
{ "gamma", "Set the float gamma value when decoding", OFFSET(gamma),
AV_OPT_TYPE_FLOAT, { .dbl = 1.0f }, 0.001, FLT_MAX, VD },
{ NULL },
};

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