From: Gonzalo Garramuno Date: Tue, 2 Dec 2014 16:48:25 +0000 (+0000) Subject: exr: Add a gamma flag to exr loader to avoid banding X-Git-Tag: android-x86-6.0-r1~10^2~402 X-Git-Url: http://git.osdn.net/view?a=commitdiff_plain;h=e0bb74a1403ed77ef369b9d62866f8a4afaf3f1d;p=android-x86%2Fexternal-ffmpeg.git 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: Vittorio Giovara --- diff --git a/libavcodec/exr.c b/libavcodec/exr.c index 4aa6eaf914..327a60e335 100644 --- a/libavcodec/exr.c +++ b/libavcodec/exr.c @@ -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 #include #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 }, };