From: Gonzalo Garramuno Date: Thu, 8 May 2014 16:27:56 +0000 (-0300) Subject: avcodec/exr: Add a gamma flag to exr loader to avoid banding X-Git-Url: https://git.sesse.net/?a=commitdiff_plain;h=cd3daad77ea420f3373d3c5feee46825d235cccc;p=ffmpeg avcodec/exr: Add a gamma flag to exr loader to avoid banding 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: Michael Niedermayer --- diff --git a/libavcodec/exr.c b/libavcodec/exr.c index 084025a3002..4898b7f56da 100644 --- a/libavcodec/exr.c +++ b/libavcodec/exr.c @@ -27,13 +27,17 @@ * 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 +#include #include "libavutil/imgutils.h" #include "libavutil/opt.h" +#include "libavutil/intfloat.h" #include "avcodec.h" #include "bytestream.h" @@ -106,8 +110,75 @@ 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 +843,7 @@ static int decode_block(AVCodecContext *avctx, void *tdata, int bxmin = s->xmin * 2 * s->desc->nb_components; int i, x, buf_size = s->buf_size; int ret; + float one_gamma = 1.0f / s->gamma; line_offset = AV_RL64(s->gb.buffer + jobnr * 8); // Check if the buffer has the required bytes needed from the offset @@ -851,18 +923,30 @@ 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)); } @@ -1261,7 +1345,10 @@ static int decode_frame(AVCodecContext *avctx, void *data, static av_cold int decode_init(AVCodecContext *avctx) { + uint32_t i; + union av_intfloat32 t; EXRContext *s = avctx->priv_data; + float one_gamma = 1.0f / s->gamma; s->avctx = avctx; s->xmin = ~0; @@ -1280,6 +1367,23 @@ 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) @@ -1322,6 +1426,8 @@ 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 }, };